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      How To Define Tasks in Ansible Playbooks



      Part of the Series:
      How To Write Ansible Playbooks

      Ansible is a modern configuration management tool that doesn’t require the use of an agent software on remote nodes, using only SSH and Python to communicate and execute commands on managed servers. This series will walk you through the main Ansible features that you can use to write playbooks for server automation. At the end, we’ll see a practical example of how to create a playbook to automate setting up a remote Nginx web server and deploy a static HTML website to it.

      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 setting up a LEMP server, you’ll need to assess which manual steps are necessary and the order in which they must be completed to get everything done. Then, you’ll be able to determine which tasks you’ll need and which modules you can use to reach your goals in less steps.

      Modules offer shortcuts to execute operations that you would otherwise have to run as raw bash commands. These are also often used to abstract commands across different operating systems.

      When you created your first playbook in a previous part of this guide, you defined a single task that outputs a message using debug. Let’s have a look at that playbook once again. You can use the cat command to print the contents of that file for examination:

      • cat ~/ansible-practice/playbook-01.yml

      This playbook contains a single task that prints a message in the output of a play:

      ~/ansible-practice/playbook-01.yml

      ---
- hosts: all
  tasks:
    - name: Print message
      debug:
        msg: Hello Ansible World

      Tasks are defined as a list under the name tasks inside a play, at the same level as the hosts directive that defines the targets for that play. The name property defines the output that will be printed out when that task is about to be executed.

      The example task invokes the debug module, which allows you to display messages in a play. These messages can be used to show debug information such as the contents of a variable or the output message returned by a command, for instance.

      Each module has its own set of options and properties. The debug module expects a property named msg containing the message to be printed out. Pay special attention to the indentation (2 spaces), since msg must be a property inside debug.



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      How To Use Variables in Ansible Playbooks



      Part of the Series:
      How To Write Ansible Playbooks

      Ansible is a modern configuration management tool that doesn’t require the use of an agent software on remote nodes, using only SSH and Python to communicate and execute commands on managed servers. This series will walk you through the main Ansible features that you can use to write playbooks for server automation. At the end, we’ll see a practical example of how to create a playbook to automate setting up a remote Nginx web server and deploy a static HTML website to it.

      Ansible supports the use of variables to better customize the execution of tasks and playbooks. This way, it’s possible to use the same playbook with different targets and environments.

      Variables can come from different sources, such as the playbook file itself or external variable files that are imported in the playbook. Special precedence rules will apply when working with multiple variable sources that define a variable with the same name.

      To see how variables work in practice, we’ll create a new test playbook that will print the value of two variables, username and home_dir. Create a new file called playbook-02.yml in your ansible-practice directory:

      • nano ~/ansible-practice/playbook-02.yml

      Then add the following lines to the new playbook file:

      ~/ansible-practice/playbook-02.yml

      ---
- hosts: all
  vars:
    - username: sammy
    - home: /home/sammy   
  tasks:
    - name: print variables
      debug:
        msg: "Username: {{ username }}, Home dir: {{ home }}"

      Save and close the file when you’re done editing.

      The vars section of the playbook defines a list of variables that will be injected in the scope of that play. All tasks, as well as any file or template that might be included in the playbook, will have access to these variables.

      To try this playbook on servers from your inventory file, run ansible-playbook with the same connection arguments you’ve used before when running our first example. Again, we’ll be using an inventory file named inventory and the sammy user to connect to the remote servers:

      • ansible-playbook -i inventory playbook-02.yml -u sammy

      You’ll see output like this:

      Output
      
PLAY [all] ***********************************************************************************************************************************************************************************

TASK [Gathering Facts] ***********************************************************************************************************************************************************************
ok: [203.0.113.10]

TASK [print variables] ***********************************************************************************************************************************************************************
ok: [203.0.113.10] => {
    "msg": "Username: sammy, Home dir: /home/sammy"
}

PLAY RECAP ***********************************************************************************************************************************************************************************
203.0.113.10              : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

      The print variables task will use the debug module to print the values of the two variables we defined in the vars section of the playbook.



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      How To Access System Information (Facts) in Ansible Playbooks



      Part of the Series:
      How To Write Ansible Playbooks

      Ansible is a modern configuration management tool that doesn’t require the use of an agent software on remote nodes, using only SSH and Python to communicate and execute commands on managed servers. This series will walk you through the main Ansible features that you can use to write playbooks for server automation. At the end, we’ll see a practical example of how to create a playbook to automate setting up a remote Nginx web server and deploy a static HTML website to it.

      By default, before executing the set of tasks defined in a playbook, Ansible will take a few moments to gather information about the systems that are being provisioned. This information, referred to as facts, contain details such as network interfaces and addresses, the operating system running on remote nodes, and available memory, among other things.

      Ansible stores facts in JSON format, with items grouped in nodes. To check what kind of information is available for the systems you’re provisioning, you can run the setup module with an ad hoc command:

      • ansible all -i inventory -m setup -u sammy

      This command will output an extensive JSON containing information about your server. To obtain a subset of that data, you can use the filter parameter and provide a pattern. For instance, if you’d like to obtain information about all IPv4 addresses in the remote nodes, you can use the following command:

      • ansible all -i inventory -m setup -a "filter=*ipv4*" -u sammy

      You’ll see output like this:

      Output
      203.0.113.10 | SUCCESS => {
    "ansible_facts": {
        "ansible_all_ipv4_addresses": [
            "203.0.113.10", 
            "198.51.100.23"
        ], 
        "ansible_default_ipv4": {
            "address": "203.0.113.10", 
            "alias": "eth0", 
            "broadcast": "203.0.113.255", 
            "gateway": "203.0.113.1", 
            "interface": "eth0", 
            "macaddress": "06:c7:91:16:2e:b7", 
            "mtu": 1500, 
            "netmask": "203.0.113.0", 
            "network": "203.0.113.0", 
            "type": "ether"
        }
    }, 
    "changed": false
}

      Once you have found the facts that will be useful for your play, you can update your playbook accordingly. As an example, the following playbook will print out the IPv4 address of the default network interface. From the previous command output, we can see that this value is available through ansible_default_ipv4.address in the JSON provided by Ansible.

      Create a new file called playbook-03.yml in your ansible-practice directory:

      • nano ~/ansible-practice/playbook-03.yml

      Then add the following lines to the new playbook file:

      ~/ansible-practice/playbook-03.yml

      ---
- hosts: all
  tasks:
    - name: print facts
      debug:
        msg: "IPv4 address: {{ ansible_default_ipv4.address }}"

      Save and close the file when you’re done.

      To try this playbook on servers from your inventory file, run ansible-playbook with the same connection arguments you’ve used before when running our first example. Again, we’ll be using an inventory file named inventory and the sammy user to connect to the remote servers:

      • ansible-playbook -i inventory playbook-03.yml -u sammy

      When you run the playbook, you’ll see your remote server’s IPv4 address in the output as expected:

      Output
      ...

TASK [print facts] ***************************************************************************************************************************************************************************
ok: [server1] => {
    "msg": "IPv4 address: 203.0.113.10"
}

...

      Facts encapsulate important data that you can leverage to better customize your playbooks. To learn more about all the information you can obtain through facts, please refer to the official Ansible documentation.



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