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How to Use Ansible Tasks When a Host Is in a Group

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Ansible Task When Host in Group

Ansible is a powerful tool for automating IT tasks. One of its most useful features is the ability to run tasks on hosts that are members of a specific group. This can be used to, for example, deploy software to a group of servers, or update the configuration of a group of devices.

In this article, we will show you how to use the `when` clause to run a task only on hosts that are members of a specific group. We will also provide some examples of how you can use this feature to automate your own tasks.

Getting Started

To follow along with this tutorial, you will need the following:

  • Ansible installed on your local machine
  • A running instance of a Linux server or virtual machine
  • A group of hosts defined in your Ansible inventory file

Once you have these prerequisites, you can start by creating a new playbook. For this example, we will call our playbook `playbook.yml`.

The `when` Clause

The `when` clause is used to conditionally execute a task. It takes a boolean expression as its argument, and the task will only be executed if the expression evaluates to `true`.

The following is an example of a `when` clause:

– name: Install Apache yum: name: httpd when: ansible_hostname in groups[‘webservers’]

In this example, the task will only be executed if the host is a member of the `webservers` group.

Here are some examples of how you can use the `when` clause to automate your tasks:

  • Deploy software to a group of servers: You can use the `when` clause to deploy software to a group of servers by using the following syntax:

when: ansible_hostname in groups[‘servers’]

  • Update the configuration of a group of devices: You can use the `when` clause to update the configuration of a group of devices by using the following syntax:

– name: Update configuration template: src: dest: when: ansible_hostname in groups[‘devices’]

The `when` clause is a powerful tool that can be used to conditionally execute tasks in Ansible. By using the `when` clause, you can automate your tasks and ensure that they are only executed on the correct hosts.

In Ansible, a task when host in group is a conditional statement that allows you to run a task only on hosts that are members of a specific group. This can be useful for running tasks that are specific to a particular group of hosts, such as deploying a new application to a group of web servers or installing a security patch on a group of workstations.

To use a task when host in group, you need to use the `when` keyword in your playbook. The `when` keyword takes a conditional statement as its argument. If the conditional statement is true, the task will be run on the hosts that are members of the specified group.

The following is an example of a playbook that uses a task when host in group:

yaml — – hosts: all tasks: – name: Install nginx apt: name: nginx state: present when: ansible_hostname in groups[‘webservers’]

In this playbook, the `install nginx` task will only be run on hosts that are members of the `webservers` group.

The syntax for a task when host in group is as follows:

when: ansible_hostname in groups[‘ ‘]

where ` ` is the name of the group that you want to target.

The following are some examples of tasks when host in group:

  • To run a task on all hosts that are members of the `webservers` group:

when: ansible_hostname in groups[‘webservers’]

  • To run a task on all hosts that are members of the `webservers` or `databases` group:

when: ansible_hostname in groups[‘webservers’] or groups[‘databases’]

  • To run a task on all hosts that are members of the `webservers` group, except for the host `web01`:

when: ansible_hostname in groups[‘webservers’] and ansible_hostname != ‘web01’

Troubleshooting

If you are having trouble getting a task when host in group to work, there are a few things you can check:

  • Make sure that the group that you are targeting exists.
  • Make sure that the hosts that you want to target are members of the group.
  • Make sure that the conditional statement is correct.

If you are still having trouble, you can post a question on the Ansible forums or ask for help on the Ansible mailing list.

A task when host in group is a powerful tool that can be used to run tasks on specific groups of hosts. By using task when host in group, you can automate tasks that are specific to a particular group of hosts, such as deploying a new application to a group of web servers or installing a security patch on a group of workstations.

3. Examples of tasks when host in group

  • Install Apache on web servers

– name: Install Apache on web servers become: yes hosts: webservers tasks: – name: Install Apache apt: name=apache2 state=present

This task will install Apache on all hosts in the `webservers` group.

  • Install Java on workstations

– name: Install Java on workstations become: yes hosts: workstations tasks: – name: Install Java apt: name=openjdk-8-jre state=present

This task will install Java on all hosts in the `workstations` group.

  • Update all hosts

– name: Update all hosts become: yes hosts: all tasks: – name: Update packages apt: update_cache=yes upgrade=yes

This task will update all packages on all hosts in the inventory.

  • Install a package on all hosts with a specific version

– name: Install Apache 2.4 on all hosts become: yes hosts: all tasks: – name: Install Apache 2.4 apt: name=apache2 state=present version=2.4.41-1ubuntu1.2

This task will install Apache 2.4 on all hosts in the inventory.

  • Install a package on all hosts with a specific release

– name: Install Apache 2.4.41-1ubuntu1.2 on all hosts become: yes hosts: all tasks: – name: Install Apache 2.4.41-1ubuntu1.2 apt: name=apache2 state=present version=2.4.41-1ubuntu1.2

This task will install Apache 2.4.41-1ubuntu1.2 on all hosts in the inventory.

  • Install a package on all hosts with a specific architecture

– name: Install Apache 2.4 on all x86_64 hosts become: yes hosts: all:!aarch64 tasks: – name: Install Apache 2.4 apt: name=apache2 state=present

This task will install Apache 2.4 on all x86_64 hosts in the inventory.

  • Install a package on all hosts with a specific OS

– name: Install Apache 2.4 on all Ubuntu 18.04 hosts become: yes hosts: ubuntu:18.04 tasks: – name: Install Apache 2.4 apt: name=apache2 state=present

This task will install Apache 2.4 on all Ubuntu 18.04 hosts in the inventory.

  • Install a package on all hosts with a specific OS release

– name: Install Apache 2.4 on all Ubuntu 18.04.5 LTS hosts become: yes hosts: ubuntu:18.04.5 tasks: – name: Install Apache 2.4 apt: name=apache2 state=present

This task will install Apache 2.4 on all Ubuntu 18.04.5 LTS hosts in the inventory.

Tasks when host in group can be a powerful tool for managing your Ansible playbooks. They allow you to run tasks on specific groups of hosts, which can save you time and effort. By using tasks when host in group, you can make your Ansible playbooks more efficient and effective.

Here are some tips for using tasks when host in group:

  • Use tasks when host in group to install software, configure systems, and perform other tasks on specific groups of hosts.
  • Use variables to define the groups of hosts that you want to target.
  • Use conditionals to only run tasks when certain conditions are met.
  • Use loops to run tasks on multiple groups of hosts.

By following these tips, you can use tasks when host in group to create Ansible playbooks that are more efficient and effective.

In this article, we have discussed the basics of tasks when host in group in Ansible. We have seen how to use tasks when host in group to install software

Q: What is the Ansible `when` clause?

A: The `when` clause in Ansible allows you to conditionally execute a task or set of tasks based on the value of a variable. This can be useful for tasks that you only want to run on certain hosts or for tasks that you only want to run under certain conditions.

Q: How do I use the `when` clause with the `host in group` condition?

A: To use the `when` clause with the `host in group` condition, you would simply specify the name of the group that you want to check for. For example, the following task would only be executed on hosts that are members of the `webservers` group:

– name: Install Apache yum: name: httpd when: host in groups[‘webservers’]

Q: What are some other common uses for the `when` clause?

A: The `when` clause can be used for a variety of other purposes, such as:

  • Checking for the existence of a file or directory
  • Checking for the value of a variable
  • Checking for the status of a service
  • Checking for the results of a command

Q: How can I use the `when` clause to avoid running tasks on hosts that I don’t want to touch?

A: You can use the `when` clause to avoid running tasks on hosts that you don’t want to touch by using the `not` operator. For example, the following task would not be executed on any hosts that are members of the `excluded_hosts` group:

– name: Install Apache yum: name: httpd when: not host in groups[‘excluded_hosts’]

Q: Can I use the `when` clause to run tasks on multiple groups of hosts?

A: Yes, you can use the `when` clause to run tasks on multiple groups of hosts by using the `or` operator. For example, the following task would be executed on hosts that are members of either the `webservers` group or the `databases` group:

– name: Install Apache yum: name: httpd when: host in groups[‘webservers’] or host in groups[‘databases’]

Q: What are the limitations of the `when` clause?

The `when` clause has a few limitations that you should be aware of:

  • The `when` clause can only be used with tasks. It cannot be used with roles or plays.
  • The `when` clause can only be used with the `and` and `or` operators. It cannot be used with other logical operators, such as `not` or `xor`.
  • The `when` clause can only be used with variables that are defined in the playbook. It cannot be used with variables that are defined in the inventory file.

Q: Where can I learn more about the Ansible `when` clause?

For more information about the Ansible `when` clause, please see the following resources:

  • [Ansible Documentation: The `when` Clause](https://docs.ansible.com/ansible/latest/user_guide/playbooks_conditionals.htmlthe-when-clause)
  • [Ansible Community Forums: The `when` Clause](https://forum.ansible.com/t/the-when-clause/2220)

We hope that this blog post has been helpful in understanding how to use the `when` clause in Ansible. For more information, please refer to the official Ansible documentation.

Here are some key takeaways from this blog post:

  • The `when` clause can be used to run a task only when a host is in a particular group.
  • The `in` operator can be used to match hosts by their name or IP address.
  • The `with_items` loop can be used to iterate over a list of hosts and run a task for each one.
  • The `filter` module can be used to filter a list of hosts based on certain criteria.

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How To Utilize Ansible Hostvars For Efficient Automation

Unlock the potential of Ansible hostvars for streamlined automation. This guide illuminates their setup and application, ensuring efficient playbook executions.

Ansible's hostvars feature offers a streamlined approach to managing host-specific variables within playbooks. It simplifies the process of assigning and accessing data unique to each host in your inventory, enhancing automation efficiency. This functionality is essential for developers seeking organized and scalable configuration management.

ansible assign task to host

Understanding Hostvars In Ansible

Defining hostvars in ansible, assigning variables for each host, accessing hostvars in playbooks, using hostvars in templates, implementing conditionals with hostvars, hostvars in facts gathering, frequently asked questions.

Hostvars are a way to store variables for each host in your Ansible inventory. These variables can be used to customize the configuration files and tasks for each host individually.

Hostvars Syntax

Utilizing hostvars in tasks, dynamic assignment of hostvars.

The basic syntax for defining hostvars is through the inventory file, typically found at /etc/ansible/hosts . Here is an example of defining a host variable directly in the inventory:

When writing tasks in your playbooks, you can refer to these variables for each specific host using the hostvars dictionary:

Hostvars can also be dynamically assigned or overridden in playbooks using the set_fact module:

By using hostvars, you can have a high degree of control over each host's settings and behavior in your Ansible-managed environments. They form the basis for dynamic and flexible playbook designs that can adapt to the specifics of each host.

Defining Hostvars in Ansible is a straightforward process. These variables are declared in the inventory file, which can be in either INI or YAML format, to assign specific values to hosts.

YAML Format

Group variables.

In the INI format inventory file, you define hostvars after the host's name:

Alternatively, in a YAML format inventory, hostvars are defined in a structured way:

Hostvars can also be defined for a group of hosts, allowing you to set common variables for multiple hosts:

Hostvars can be particularly useful for setting up environment-specific configurations without altering playbooks. They are a fundamental feature for Ansible users looking to manage complex environments with ease.

Assigning Variables to each host in Ansible is done through the inventory, where you can specify variables that apply to individual hosts. These variables can dictate host-specific settings for tasks and templates.

Host-Specific Variables

Overriding group variables.

To assign a variable to a host, list it beneath the host’s entry in the inventory file. Here's a YAML inventory example:

If a host is part of a group with its variables, you can still assign host-specific variables that override the group settings:

By using this method, you can tailor the behavior of your Ansible managed systems, ensuring that each host is configured with the appropriate settings. This approach is key to maintaining scalability and flexibility in your infrastructure.

Accessing Hostvars in playbooks is essential for applying host-specific configurations. These variables are referenced via the hostvars dictionary provided by Ansible.

Referencing Hostvars

Iterating over all hosts.

Variables assigned to a host can be accessed using the hostvars dictionary with the host's name or the special variable inventory_hostname for the current host in the playbook:

To iterate over all hosts and access their variables, you can loop through the ansible_play_hosts list:

Using hostvars in this manner provides a powerful way to leverage the inventory data within your playbooks, ensuring that tasks are executed with the appropriate context for each host.

Using Hostvars in Templates allows you to create dynamic files that adapt to the characteristics of each host. Templates in Ansible use the Jinja2 templating language to achieve this.

Injecting Hostvars Into Templates

Applying templates in playbooks.

When creating a template, hostvars can be inserted into the file using Jinja2 syntax. For example:

To apply a template to your hosts, use the template module in a playbook task:

Templates are a fundamental feature for ensuring that each host is configured with settings that reflect its role and characteristics. By utilizing hostvars within templates, Ansible can manage complex configurations with ease.

Implementing Conditionals with Hostvars enhances playbook flexibility by executing tasks based on specific host variables.

Using When Statements

Combining hostvars with conditionals.

Conditionals in Ansible are implemented with the when statement. This statement checks the value of a hostvar and decides whether to run a task:

ansible assign task to host

You can combine multiple hostvars within a conditional to create complex logic:

ansible assign task to host

Through the use of conditionals with hostvars, Ansible playbooks can perform tasks that are finely tuned to the characteristics and roles of each host in the inventory. This approach is key to creating robust and adaptable automation routines.

Hostvars in Facts Gathering is a critical aspect of Ansible's configuration management capabilities. Facts are pieces of information derived from speaking with your remote systems.

Gathering Facts

Custom facts, using facts in playbooks.

By default, Ansible gathers facts about hosts at the beginning of a playbook run. This includes information like network interfaces, operating system, and services. These facts are stored in hostvars:

ansible assign task to host

You can also create custom facts by placing executable files or scripts in the /etc/ansible/facts.d directory on the managed hosts. These scripts output JSON data, which Ansible converts into hostvars:

Once gathered, facts can be used just like regular hostvars:

Facts are a powerful way to make decisions in playbooks based on the actual state of the host. They form the basis for conditionals, templates, and even the dynamic inclusion of tasks or roles based on the host's properties.

Is It Possible To Override Hostvars?

Yes, hostvars can be overridden in different contexts, such as within a playbook using the set_fact module or by specifying different values for the same variable in different inventory files or groups.

Can I Use Hostvars in Templates?

Absolutely. Hostvars can be integrated into Jinja2 templates, allowing you to generate dynamic files based on each host's specific variables.

Can Hostvars Be Used Across Different Playbooks?

Yes, hostvars set for a host are accessible in any playbook that includes that host, making them reusable across different playbooks.

What's the Best Practice for Securing Sensitive Hostvars?

Sensitive hostvars, like passwords or API keys, should be encrypted using Ansible Vault to ensure security and prevent exposure in plain text.

Let’s test your knowledge!

What is the purpose of hostvars in Ansible?

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how to access host variable of a different host with Ansible?

Let's say I have a host that collects some data and it's in a group [collectors] . I also have hosts in-group [reporters] . So, I want to set a variable on reporters from groups['collectors'][0] IP address. But the playbook for setting up reporters doesn't run on [collectors] group so facts for this host are not collected. Is there a way not to hardcode the IP address?

AATHITH RAJENDRAN's user avatar

You can access pretty much any inventory facts/variables by doing something like this:

or, if you want to do it via an index into a group:

The big trick is that you need to collect the facts for all the hosts/groups you're interested in. So you would want to modify your playbook that runs against the reporters group to include a no-op (dummy) task that is applied to the collectors group. That will cause Ansible to collect facts about the collectors hosts so that they can be accessed from the reporters group. So you might want to add something like this to the top of your reporters playbook:

The empty brackets basically mean that no tasks will be executed, but this will still force Ansible to gather facts about the collectors so that you can then reference them in the tasks that you run against your reporters.

It occurred to me that I should also mention that as of version 1.8 of Ansible, there is a fact-caching feature that is now available. Fact caching relies on a redis server to store facts between playbook runs. With it enabled, one playbook can reference facts that were obtained by another playbook that was run previously. The example the Ansible documentation gives:

Imagine, for instance, a very large infrastructure with thousands of hosts. Fact caching could be configured to run nightly, but configuration of a small set of servers could run ad-hoc or periodically throughout the day. With fact-caching enabled, it would not be necessary to “hit” all servers to reference variables and information about them.

slm's user avatar

  • 3 Is there a way to set associative index as a variable? in example ansible localhost --extra-vars "metamorphosis_ip=172.16.3.73" -a "echo {{ hostvars[{{ metamorphosis_ip }}]['inv_domain'] }} " –  corretge May 2, 2016 at 16:26
  • To add to the answer above above make sure that you reference the Ansible FAQ here: docs.ansible.com/ansible/faq.html which explains things in detail, like looping over a group of hosts or setting a variable to get an specific host in a group. –  eco Jun 2, 2016 at 5:22
  • Thank you for the idea of fetching facts from a node with an empty task list. –  pedz Aug 24, 2018 at 22:18
  • @corretge Yes, you can do this by simply referring to the variable directly without quotes: {{ hostvars[metamorphosis_ip]['inv_domain'] }} –  DaVince Aug 5, 2020 at 15:53
  • 3 It seems that the names of the facts have changed somewhat since this was posted. To get this work I had to change this to {{ hostvars[groups['collectors'][0]]['ansible_default_ipv4']['address'] }} –  Bram Jan 5, 2021 at 13:01

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How to build your inventory 

Ansible automates tasks on managed nodes or “hosts” in your infrastructure, using a list or group of lists known as inventory. You can pass host names at the command line, but most Ansible users create inventory files. Your inventory defines the managed nodes you automate, with groups so you can run automation tasks on multiple hosts at the same time. Once your inventory is defined, you use patterns to select the hosts or groups you want Ansible to run against.

The simplest inventory is a single file with a list of hosts and groups. The default location for this file is /etc/ansible/hosts . You can specify a different inventory file at the command line using the -i <path> option or in configuration using inventory .

Ansible Inventory plugins supports a range of formats and sources to make your inventory flexible and customizable. As your inventory expands, you may need more than a single file to organize your hosts and groups. Here are three options beyond the /etc/ansible/hosts file:

You can create a directory with multiple inventory files. See Organizing inventory in a directory . These can use different formats (YAML, ini, and so on).

You can pull inventory dynamically. For example, you can use a dynamic inventory plugin to list resources in one or more cloud providers. See Working with dynamic inventory .

You can use multiple sources for inventory, including both dynamic inventory and static files. See Passing multiple inventory sources .

The following YAML snippets include an ellipsis to indicate they are part of a larger YAML file. You can find out more about YAML syntax at YAML Basics .

Inventory basics: formats, hosts, and groups 

You can create your inventory file in one of many formats, depending on the inventory plugins you have. The most common formats are INI and YAML. A basic INI /etc/ansible/hosts might look like this:

The headings in brackets are group names, which are used in classifying hosts and deciding what hosts you are controlling at what times and for what purpose. Group names should follow the same guidelines as Creating valid variable names .

Here’s that same basic inventory file in YAML format:

Default groups 

Even if you do not define any groups in your inventory file, Ansible creates two default groups: all and ungrouped . The all group contains every host. The ungrouped group contains all hosts that don’t have another group aside from all . Every host will always belong to at least 2 groups ( all and ungrouped or all and some other group). For example, in the basic inventory above, the host mail.example.com belongs to the all group and the ungrouped group; the host two.example.com belongs to the all group and the dbservers group. Though all and ungrouped are always present, they can be implicit and not appear in group listings like group_names .

Hosts in multiple groups 

You can put each host in more than one group. For example, a production web server in a data center in Atlanta might be included in groups called [prod] and [atlanta] and [webservers] . You can create groups that track:

What - An application, stack or microservice (for example, database servers, web servers, and so on).

Where - A datacenter or region, to talk to local DNS, storage, and so on (for example, east, west).

When - The development stage, to avoid testing on production resources (for example, prod, test).

Extending the previous YAML inventory to include what, when, and where would look like this:

You can see that one.example.com exists in the dbservers , east , and prod groups.

Grouping groups: parent/child group relationships 

You can create parent/child relationships among groups. Parent groups are also known as nested groups or groups of groups. For example, if all your production hosts are already in groups such as atlanta_prod and denver_prod , you can create a production group that includes those smaller groups. This approach reduces maintenance because you can add or remove hosts from the parent group by editing the child groups.

To create parent/child relationships for groups:

in INI format, use the :children suffix

in YAML format, use the children: entry

Here is the same inventory as shown above, simplified with parent groups for the prod and test groups. The two inventory files give you the same results:

Child groups have a couple of properties to note:

Any host that is a member of a child group is automatically a member of the parent group.

Groups can have multiple parents and children, but not circular relationships.

Hosts can also be in multiple groups, but there will only be one instance of a host at runtime. Ansible merges the data from multiple groups.

Adding ranges of hosts 

If you have a lot of hosts with a similar pattern, you can add them as a range rather than listing each hostname separately:

You can specify a stride (increments between sequence numbers) when defining a numeric range of hosts:

The example above would make the subdomains www01, www03, www05, …, www49 match, but not www00, www02, www50 and so on, because the stride (increment) is 2 units each step.

For numeric patterns, leading zeros can be included or removed, as desired. Ranges are inclusive. You can also define alphabetic ranges:

Passing multiple inventory sources 

You can target multiple inventory sources (directories, dynamic inventory scripts or files supported by inventory plugins) at the same time by giving multiple inventory parameters from the command line or by configuring ANSIBLE_INVENTORY . This can be useful when you want to target normally separate environments, like staging and production, at the same time for a specific action.

To target two inventory sources from the command line:

Organizing inventory in a directory 

You can consolidate multiple inventory sources in a single directory. The simplest version of this is a directory with multiple files instead of a single inventory file. A single file gets difficult to maintain when it gets too long. If you have multiple teams and multiple automation projects, having one inventory file per team or project lets everyone easily find the hosts and groups that matter to them.

You can also combine multiple inventory source types in an inventory directory. This can be useful for combining static and dynamic hosts and managing them as one inventory. The following inventory directory combines an inventory plugin source, a dynamic inventory script, and a file with static hosts:

You can target this inventory directory as follows:

You can also configure the inventory directory in your ansible.cfg file. See Configuring Ansible for more details.

Managing inventory load order 

Ansible loads inventory sources in ASCII order according to the filenames. If you define parent groups in one file or directory and child groups in other files or directories, the files that define the child groups must be loaded first. If the parent groups are loaded first, you will see the error Unable to parse /path/to/source_of_parent_groups as an inventory source .

For example, if you have a file called groups-of-groups that defines a production group with child groups defined in a file called on-prem , Ansible cannot parse the production group. To avoid this problem, you can control the load order by adding prefixes to the files:

You can find examples of how to organize your inventories and group your hosts in Inventory setup examples .

Adding variables to inventory 

You can store variable values that relate to a specific host or group in inventory. To start with, you may add variables directly to the hosts and groups in your main inventory file.

We document adding variables in the main inventory file for simplicity. However, storing variables in separate host and group variable files is a more robust approach to describing your system policy. Setting variables in the main inventory file is only a shorthand. See Organizing host and group variables for guidelines on storing variable values in individual files in the ‘host_vars’ directory. See Organizing host and group variables for details.

Assigning a variable to one machine: host variables 

You can easily assign a variable to a single host and then use it later in playbooks. You can do this directly in your inventory file.

Unique values like non-standard SSH ports work well as host variables. You can add them to your Ansible inventory by adding the port number after the hostname with a colon:

Connection variables also work well as host variables:

If you list non-standard SSH ports in your SSH config file, the openssh connection will find and use them, but the paramiko connection will not.

Inventory aliases 

You can also define aliases in your inventory using host variables:

In this example, running Ansible against the host alias “jumper” will connect to 192.0.2.50 on port 5555. See behavioral inventory parameters to further customize the connection to hosts.

Defining variables in INI format 

Values passed in the INI format using the key=value syntax are interpreted differently depending on where they are declared:

When declared inline with the host, INI values are interpreted as Python literal structures (strings, numbers, tuples, lists, dicts, booleans, None). Host lines accept multiple key=value parameters per line. Therefore they need a way to indicate that a space is part of a value rather than a separator. Values that contain whitespace can be quoted (single or double). See the Python shlex parsing rules for details.

When declared in a :vars section, INI values are interpreted as strings. For example var=FALSE would create a string equal to ‘FALSE’. Unlike host lines, :vars sections accept only a single entry per line, so everything after the = must be the value for the entry.

If a variable value set in an INI inventory must be a certain type (for example, a string or a boolean value), always specify the type with a filter in your task. Do not rely on types set in INI inventories when consuming variables.

Consider using YAML format for inventory sources to avoid confusion on the actual type of a variable. The YAML inventory plugin processes variable values consistently and correctly.

Assigning a variable to many machines: group variables 

If all hosts in a group share a variable value, you can apply that variable to an entire group at once.

Group variables are a convenient way to apply variables to multiple hosts at once. Before executing, however, Ansible always flattens variables, including inventory variables, to the host level. If a host is a member of multiple groups, Ansible reads variable values from all of those groups. If you assign different values to the same variable in different groups, Ansible chooses which value to use based on internal rules for merging .

Inheriting variable values: group variables for groups of groups 

You can apply variables to parent groups (nested groups or groups of groups) as well as to child groups. The syntax is the same: :vars for INI format and vars: for YAML format:

A child group’s variables will have higher precedence (override) than a parent group’s variables.

Organizing host and group variables 

Although you can store variables in the main inventory file, storing separate host and group variables files may help you organize your variable values more easily. You can also use lists and hash data in host and group variables files, which you cannot do in your main inventory file.

Host and group variable files must use YAML syntax. Valid file extensions include ‘.yml’, ‘.yaml’, ‘.json’, or no file extension. See YAML Syntax if you are new to YAML.

Ansible loads host and group variable files by searching paths relative to the inventory file or the playbook file. If your inventory file at /etc/ansible/hosts contains a host named ‘foosball’ that belongs to two groups, ‘raleigh’ and ‘webservers’, that host will use variables in YAML files at the following locations:

For example, if you group hosts in your inventory by datacenter, and each datacenter uses its own NTP server and database server, you can create a file called /etc/ansible/group_vars/raleigh to store the variables for the raleigh group:

You can also create directories named after your groups or hosts. Ansible will read all the files in these directories in lexicographical order. An example with the ‘raleigh’ group:

All hosts in the ‘raleigh’ group will have the variables defined in these files available to them. This can be very useful to keep your variables organized when a single file gets too big, or when you want to use Ansible Vault on some group variables.

For ansible-playbook you can also add group_vars/ and host_vars/ directories to your playbook directory. Other Ansible commands (for example, ansible , ansible-console , and so on) will only look for group_vars/ and host_vars/ in the inventory directory. If you want other commands to load group and host variables from a playbook directory, you must provide the --playbook-dir option on the command line. If you load inventory files from both the playbook directory and the inventory directory, variables in the playbook directory will override variables set in the inventory directory.

Keeping your inventory file and variables in a git repo (or other version control) is an excellent way to track changes to your inventory and host variables.

How variables are merged 

By default, variables are merged/flattened to the specific host before a play is run. This keeps Ansible focused on the Host and Task, so groups do not survive outside of inventory and host matching. By default, Ansible overwrites variables including the ones defined for a group and/or host (see DEFAULT_HASH_BEHAVIOUR ). The order/precedence is (from lowest to highest):

all group (because it is the ‘parent’ of all other groups)

parent group

child group

By default, Ansible merges groups at the same parent/child level in ASCII order, and variables from the last group loaded overwrite variables from the previous groups. For example, an a_group will be merged with b_group and b_group vars that match will overwrite the ones in a_group .

Ansible merges variables from different sources and applies precedence to some variables over others according to a set of rules. For example, variables that occur higher in an inventory can override variables that occur lower in the inventory. See Variable precedence: Where should I put a variable? for more information.

You can change this behavior by setting the group variable ansible_group_priority to change the merge order for groups of the same level (after the parent/child order is resolved). The larger the number, the later it will be merged, giving it higher priority. This variable defaults to 1 if not set. For example:

In this example, if both groups have the same priority, the result would normally have been testvar == b , but since we are giving the a_group a higher priority the result will be testvar == a .

ansible_group_priority can only be set in the inventory source and not in group_vars/, as the variable is used in the loading of group_vars.

Managing inventory variable load order 

When using multiple inventory sources, keep in mind that any variable conflicts are resolved according to the rules described in How variables are merged and Variable precedence: Where should I put a variable? . You can control the merging order of variables in inventory sources to get the variable value you need.

When you pass multiple inventory sources at the command line, Ansible merges variables in the order you pass those parameters. If [all:vars] in staging inventory defines myvar = 1 and production inventory defines myvar = 2 , then:

Pass -i staging -i production to run the playbook with myvar = 2 .

Pass -i production -i staging to run the playbook with myvar = 1 .

When you put multiple inventory sources in a directory, Ansible merges them in ASCII order according to the filenames. You can control the load order by adding prefixes to the files:

If 01-openstack.yml defines myvar = 1 for the group all , 02-dynamic-inventory.py defines myvar = 2 , and 03-static-inventory defines myvar = 3 , the playbook will be run with myvar = 3 .

For more details on inventory plugins and dynamic inventory scripts see Inventory plugins and Working with dynamic inventory .

Connecting to hosts: behavioral inventory parameters 

As described above, setting the following variables controls how Ansible interacts with remote hosts.

Host connection:

Ansible does not expose a channel to allow communication between the user and the ssh process to accept a password manually to decrypt an ssh key when using the ssh connection plugin (which is the default). The use of ssh-agent is highly recommended.

Connection type to the host. This can be the name of any Ansible connection plugin. SSH protocol types are smart , ssh or paramiko . The default is smart. Non-SSH based types are described in the next section.

General for all connections:

The name of the host to connect to, if different from the alias you wish to give to it.

The connection port number, if not the default (22 for ssh)

The username to use when connecting to the host

The password to use to authenticate to the host (never store this variable in plain text; always use a vault. See Keep vaulted variables safely visible )

Specific to the SSH connection:

Private key file used by SSH. Useful if using multiple keys and you do not want to use SSH agent.

This setting is always appended to the default command line for sftp , scp , and ssh . Useful to configure a ProxyCommand for a certain host (or group).

This setting is always appended to the default sftp command line.

This setting is always appended to the default scp command line.

This setting is always appended to the default ssh command line.

Determines whether or not to use SSH pipelining. This can override the pipelining setting in ansible.cfg .

This setting overrides the default behavior to use the system ssh . This can override the ssh_executable setting in ansible.cfg under ssh_connection .

Privilege escalation (see Ansible Privilege Escalation for further details):

Equivalent to ansible_sudo or ansible_su , allows to force privilege escalation

Allows to set privilege escalation method

Equivalent to ansible_sudo_user or ansible_su_user , allows you to set the user you become through privilege escalation

Equivalent to ansible_sudo_password or ansible_su_password , allows you to set the privilege escalation password (never store this variable in plain text; always use a vault. See Keep vaulted variables safely visible )

Equivalent to ansible_sudo_exe or ansible_su_exe , allows you to set the executable for the escalation method selected

Equivalent to ansible_sudo_flags or ansible_su_flags , allows you to set the flags passed to the selected escalation method. This can be also set globally in ansible.cfg in the become_flags option under privilege_escalation .

Remote host environment parameters:

The shell type of the target system. You should not use this setting unless you have set the ansible_shell_executable to a non-Bourne (sh) compatible shell. By default, commands are formatted using sh -style syntax. Setting this to csh or fish will cause commands executed on target systems to follow those shell’s syntax instead.

The target host Python path. This is useful for systems with more than one Python or not located at /usr/bin/python such as *BSD, or where /usr/bin/python is not a 2.X series Python. We do not use the /usr/bin/env mechanism as that requires the remote user’s path to be set right and also assumes the python executable is named python, where the executable might be named something like python2.6 .

Works for anything such as ruby or perl and works just like ansible_python_interpreter . This replaces shebang of modules that will run on that host.

New in version 2.1.

This sets the shell the ansible control node will use on the target machine, overrides executable in ansible.cfg which defaults to /bin/sh . You should only change this value if it is not possible to use /bin/sh (in other words, if /bin/sh is not installed on the target machine or cannot be run from sudo.).

Examples from an Ansible-INI host file:

Non-SSH connection types 

As stated in the previous section, Ansible executes playbooks over SSH but it is not limited to this connection type. With the host-specific parameter ansible_connection=<connector> , the connection type can be changed. For a full list with available plugins and examples, see Plugin list .

Inventory setup examples 

See also Sample Ansible setup , which shows inventory along with playbooks and other Ansible artifacts.

Example: One inventory per environment 

If you need to manage multiple environments it is sometimes prudent to have only hosts of a single environment defined per inventory. This way, it is harder to, for example, accidentally change the state of nodes inside the “test” environment when you wanted to update some “staging” servers.

For the example mentioned above you could have an inventory_test file:

That file only includes hosts that are part of the “test” environment. Define the “staging” machines in another file called inventory_staging :

To apply a playbook called site.yml to all the app servers in the test environment, use the following command:

Example: Group by function 

In the previous section, you already saw an example of using groups in order to cluster hosts that have the same function. This allows you, for example, to define firewall rules inside a playbook or role affecting only database servers:

Example: Group by location 

Other tasks might be focused on where a certain host is located. Let’s say that db01.test.example.com and app01.test.example.com are located in DC1 while db02.test.example.com is in DC2:

In practice, you might even end up mixing all these setups as you might need to, on one day, update all nodes in a specific data center while, on another day, update all the application servers no matter their location.

Pulling inventory from dynamic or static sources

Pulling inventory from dynamic sources, such as cloud providers

Examples of basic commands

Learning Ansible’s configuration, deployment, and orchestration language.

Questions? Help? Ideas? Stop by the list on Google Groups

How to join Ansible chat channels

IMAGES

  1. Ansible delegate_to Examples

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  2. Using Ansible To Manage Hostnames In Group: A Comprehensive Guide

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  3. Ansible Hosts File

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  4. Ansible delegate_to Examples

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  5. Ansible add_host

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  6. Getting started with Ansible 15

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VIDEO

  1. How to Assign Task

  2. Assign Task and keyframe

  3. [Short] Creating A Simple INI And YAML Ansible Inventory #ansible #automation #devops #ini #yaml

  4. Ansible Server Provisioning

  5. Chapter 4. Conditional Task in Arabic Eng. (Alaa Mohammed)

  6. PART 1

COMMENTS

  1. Controlling where tasks run: delegation and local actions

    By default, Ansible gathers facts and executes all tasks on the machines that match the hosts line of your playbook. This page shows you how to delegate tasks to a different machine or group, delegate facts to specific machines or groups, or run an entire playbook locally.

  2. how to run a particular task on specific host in ansible

    how to run a particular task on specific host in ansible - Stack Overflow how to run a particular task on specific host in ansible Ask Question Asked 8 years, 6 months ago Modified 1 year, 6 months ago Viewed 102k times 46 my inventory file's contents - [webservers] x.x.x.x ansible_ssh_user=ubuntu [dbservers] x.x.x.x ansible_ssh_user=ubuntu

  3. Controlling playbook execution: strategies and more

    By default, Ansible runs each task on all hosts affected by a play before starting the next task on any host, using 5 forks. If you want to change this default behavior, you can use a different strategy plugin, change the number of forks, or apply one of several keywords like serial. Selecting a strategy Setting the number of forks

  4. ansible

    1 This is a duplicate of this StackOverflow question. But I will combine and summarize all the answers here. If your "other_host" is in the playbooks inventory then you can use the when keyword: when: inventory_hostname is "other_host" . Which will only run that task once and only for "other_host".

  5. How To Define Tasks in Ansible Playbooks

    A task is the smallest unit of action you can automate using an Ansible playbook. Playbooks typically contain a series of tasks that serve a goal, such as to set up a web server, or to deploy an application to remote environments. Ansible executes tasks in the same order they are defined inside a playbook. Before automating a procedure such as ...

  6. Ansible: How to run one Task Host by Host?

    7 Answers Sorted by: 22 You can run a single task in serial (i.e. host-by-host) by adding throttle: 1 to it. Example: --- - hosts: all tasks: - name: wait in parallel command: sleep 20 - name: wait in serial command: sleep 30 throttle: 1 References: Using keywords to control execution Playbook Keywords: Tasks

  7. How to Use Ansible Tasks When a Host Is in a Group

    package: name: when: ansible_hostname in groups ['servers'] Update the configuration of a group of devices: You can use the `when` clause to update the configuration of a group of devices by using the following syntax: - name: Update configuration template: src: dest: when: ansible_hostname in groups ['devices']

  8. How To Efficiently Manage Ansible Hosts

    Ansible communicates with nodes using SSH. It's crucial to set up SSH keys for a passwordless login. Generate an SSH key pair: # Generate an SSH key ssh-keygen -t rsa -b 4096. Copy the public key to your managed nodes: # Copy SSH public key to a managed node ssh-copy-id user@remote-host.

  9. How To Utilize Ansible Hostvars For Efficient Automation

    Ansible's hostvars feature offers a streamlined approach to managing host-specific variables within playbooks. It simplifies the process of assigning and accessing data unique to each host in your inventory, enhancing automation efficiency. This functionality is essential for developers seeking organized and scalable configuration management.

  10. Executing specific tasks against specific hosts in an Ansible playbook

    Ansible playbooks only have one for declaring hosts, which is right at the top and all the tasks execute against the specified hosts. But what I hope to achieve is: Tasks 1 to 10 execute against the vig group Tasks 11 to 20 execute against the websvr group All in the same playbook, as in: ansible-playbook -i <inventory file> deploy.yml.

  11. In Ansible, how do I assign a hostvar to a playbook's host?

    - name: Add the provisioned AWS instance to the inventory add_host: name: " { { aws_instance_public_ip.value }}" # set using set_fact elsewhere in file ansible_user: " { { aws_instance_user_name }}" groups: " { { aws_instance_host_group }}"

  12. Handlers: running operations on change

    Sometimes you want a task to run only when a change is made on a machine. For example, you may want to restart a service if a task updates the configuration of that service, but not if the configuration is unchanged. Ansible uses handlers to address this use case. Handlers are tasks that only run when notified. Handler example. Notifying handlers.

  13. How can I assign an ansible variable which is avaiable across tasks

    New to ansible - I'm trying to set the PS1 variable in /etc/bash.bashrc based on the condition of the host's IP address. ... Is there a way to define the ps1 variable so I can assign it inside a task and have it available to other tasks?--- - hosts: all tasks: - name: generate LAN host bash prompt when: ansible_default_ipv4.address is match ...

  14. ansible

    ansible - Select host to execute task based on multiple conditions - Stack Overflow Select host to execute task based on multiple conditions Ask Question Asked 3 years, 5 months ago Viewed 807 times 2 Using Ansible v2.9.12 Imagine 4 hosts in a play, with the following vars:

  15. Listing All Ansible Variables for a Host or Group

    Ansible uses the debug module for showing variables or messages on stdout when a playbook runs.Several parameters are used with this module: msg: string-type parameter that prints a custom message; var: variable to be debugged with msg and var being mutually exclusive; verbosity: level at which the debug operation runs (e.g., for value of 3, debug runs with -vvv)

  16. how to access host variable of a different host with Ansible?

    - hosts: collectors name: Gather facts from collectors tasks: [ ] The empty brackets basically mean that no tasks will be executed, but this will still force Ansible to gather facts about the collectors so that you can then reference them in the tasks that you run against your reporters. Edit #1

  17. Using Variables

    Ansible uses variables to manage differences between systems. With Ansible, you can execute tasks and playbooks on multiple different systems with a single command. To represent the variations among those different systems, you can create variables with standard YAML syntax, including lists and dictionaries.

  18. Run an Ansible task to all hosts if at least one of the hosts has a

    1 extract the variables, select true items and evaluate the test is any, e.g. - set_fact: semaphore: " { { ansible_play_hosts_all| map ('extract', hostvars, 'new_node')| select is any }}" run_once: true gives true if any variable new_node is true and gives false otherwise semaphore: true Then use the variable semaphore in the conditions e.g.

  19. How to build your inventory

    Ansible automates tasks on managed nodes or "hosts" in your infrastructure, using a list or group of lists known as inventory. You can pass host names at the command line, but most Ansible users create inventory files.

  20. Ansible variables assign to host

    1 Make sure host_vars is relative to playbook, in this case mytest.yml: