Red Hat Ansible for Network Automation

After completing this section, you should be able to:

Filters in Ansible are from Jinja2, and are used for transforming data inside a template expression.

Filters are available for a wide variety of use cases.

For example, to transform the CIDR form of an IPv4 address into a host address, you can use the ipaddr filter:

{{ '192.0.2.1/24' | ipaddr('address') }}

This returns the value 192.0.2.1.

You can use the same Jinja2 filter with a different argument to extract the variable-length subnet mask from that specification:

{{ '192.0.2.1/24' | ipaddr('netmask') }}

This returns the value 255.255.255.0. You can use the prefix argument with the ipaddr filter if you want the CIDR prefix for that subnet mask instead.

A network CLI filter is available that, when used in conjunction with a parser specification, automatically parses a network device CLI command output into structured JSON form.

---
- name: a play that shows parsed interface data
  hosts: ios
  gather_facts: no
  vars:
    shint_parser: vars/ios-shipintbr-parser.yml

  tasks:
    - name: issue commands
      ios_command:
        commands:
          - show ip interface brief
        register: results

    - name: show CLI output
      debug:
        msg: "{{ results.stdout[0] | parse_cli(shint_parser) }}"

Jinja2 tests evaluate template expressions and return a True or False result.

You can use these expressions to conditionally run tasks. The when directive only runs a task if its condition or list of conditions are True.

tasks:
  - name: run a command
    vyos_command:
      commands:
        - show interface ethernet eth2
    register: result
    ignore_errors: True

  - debug:
      msg: "show interface ethernet eth2 failed, interface might not be present"
    when: result is failed

In this example, the expression result is failed is a Jinja2 test.