Network Automation with Red Hat Ansible Automation Platform

Ansible applies variable values to playbooks and templates by using Jinja2 expressions. For example, the following Jinja2 expression replaces the name of the variable inside the double braces with its value:

{{ variable }}

Jinja2 expressions also support filters. Filters are used to modify or process the value from the variable that is placed in the playbook or template. Some filters are provided by the Jinja2 language; others are included with Red Hat Ansible Automation Platform as plug-ins. You can also create custom filters. Filters can be extremely useful for preparing data for use in your playbook or template.

To use a filter in a Jinja2 expression, add a pipe (|) character after the variable name or value and then write the filter or filter expression. You can specify multiple filters in a pipeline, separating each filter or filter expression with a pipe character.

{{ variable | filter }}

A number of filters and lookup plug-ins are available to collect and process network information for Ansible automation. These filters and plug-ins can be useful with fact gathering when you configure the network managed nodes in your environment.

You can validate and manipulate networking data stored in variables and facts with the ansible.utils.ipaddr filter. The ansible.utils.ipaddr filter can validate the syntax of IP addresses, filter out bad data, convert from Variable Length Subnet Mask (VLSM) to Classless Inter-domain Routing (CIDR) subnet prefix notation, perform subnet math, or find the next usable address in a network range.

This section explores some uses of the ansible.utils.ipaddr filter.

{{ my_hosts_list | ansible.utils.ipaddr }}

Several general purpose filters are available for you to use in your playbooks. The following table briefly describes some of these filters:

Several of the filters in the previous table are available as part of the ansible-core RPM package. If the ansible-core package is installed on your local machine, then you can list all the files in that package and search for a specific plug-in.

[user@host ~]$ rpm -ql ansible-core | grep to_nice_yaml
/usr/lib/python3.9/site-packages/ansible/plugins/filter/to_nice_yaml.yml

After you identify the location of one plug-in, you can find additional plug-ins in the same directory:

[user@host ~]$ ls /usr/lib/python3.9/site-packages/ansible/plugins/filter/
__init__.py      flatten.yml        random.yml               to_nice_json.yml
__pycache__      from_json.yml      realpath.yml             to_nice_yaml.yml
b64decode.yml    from_yaml.yml      regex_escape.yml         to_uuid.yml
b64encode.yml    from_yaml_all.yml  regex_findall.yml        to_yaml.yml
basename.yml     hash.yml           regex_replace.yml        type_debug.yml
bool.yml         human_readable.yml regex_search.yml         union.yml
checksum.yml     human_to_bytes.yml rekey_on_member.yml      unique.yml
combinations.yml intersect.yml      relpath.yml              unvault.yml
combine.yml      items2dict.yml     root.yml                 urldecode.yml
comment.yml      log.yml            sha1.yml                 urls.py
core.py          mandatory.yml      shuffle.yml              urlsplit.py
dict2items.yml   mathstuff.py       split.yml                vault.yml
difference.yml   md5.yml            splitext.yml             win_basename.yml
dirname.yml      password_hash.yml  strftime.yml             win_dirname.yml
encryption.py    path_join.yml      subelements.yml          win_splitdrive.yml
expanduser.yml   permutations.yml   symmetric_difference.yml zip.yml
expandvars.yml   pow.yml            ternary.yml              zip_longest.yml
extract.yml      product.yml        to_datetime.yml
fileglob.yml     quote.yml          to_json.yml

The other filters from the table are Jinja2 built-in filters. You can find more information about both types of filters using the links in the References section.