10 Ansible modules you need to know

Ansible is an open source IT configuration management and automation platform. It uses human-readable YAML templates so users can program repetitive tasks to happen automatically without having to learn an advanced programming language.

Ansible is agentless, which means the nodes it manages do not require any software to be installed on them. This eliminates potential security vulnerabilities and makes overall management smoother.

Ansible modules are standalone scripts that can be used inside an Ansible playbook. A playbook consists of a play, and a play consists of tasks. These concepts may seem confusing if you're new to Ansible, but as you begin writing and working more with playbooks, they will become familiar.

There are some modules that are frequently used in automating everyday tasks; those are the ones that we will cover in this article.

Ansible has three main files that you need to consider:

• Host/inventory file: Contains the entry of the nodes that need to be managed
• Ansible.cfg file: Located by default at /etc/ansible/ansible.cfg, it has the necessary privilege escalation options and the location of the inventory file
• Main file: A playbook that has modules that perform various tasks on a host listed in an inventory or host file

Module 1: Package management

There is a module for most popular package managers, such as DNF and APT, to enable you to install any package on a system. Functionality depends entirely on the package manager, but usually these modules can install, upgrade, downgrade, remove, and list packages. The names of relevant modules are easy to guess. For example, the DNF module is dnf_module, the old YUM module (required for Python 2 compatibility) is yum_module, while the APT module is apt_module, the Slackpkg module is slackpkg_module, and so on.

Example 1:

- name: install the latest version of Apache and MariaDB
  dnf:
    name:
      - httpd
      - mariadb-server
    state: latest

This installs the Apache web server and the MariaDB SQL database.

Example 2:

- name: Install a list of packages
  yum:
    name:
      - nginx
      - postgresql
      - postgresql-server
    state: present

This installs the list of packages and helps download multiple packages.

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Module 2: Service

After installing a package, you need a module to start it. The service module enables you to start, stop, and reload installed packages; this comes in pretty handy.

Example 1:

- name: Start service foo, based on running process /usr/bin/foo
  service:
    name: foo
    pattern: /usr/bin/foo
    state: started

This starts the service foo.

Example 2:

- name: Restart network service for interface eth0
  service:
    name: network
    state: restarted
    args: eth0

This restarts the network service of the interface eth0.

Module 3: Copy

The copy module copies a file from the local or remote machine to a location on the remote machine.

Example 1:

- name: Copy a new "ntp.conf file into place, backing up the original if it differs from the copied version
  copy:
    src: /mine/ntp.conf
    dest: /etc/ntp.conf
    owner: root
    group: root
    mode: '0644'
    backup: yes

Example 2:

- name: Copy file with owner and permission, using symbolic representation
  copy:
    src: /srv/myfiles/foo.conf
    dest: /etc/foo.conf
    owner: foo
    group: foo
    mode: u=rw,g=r,o=r

Module 4: Debug

The debug module prints statements during execution and can be useful for debugging variables or expressions without having to halt the playbook.

Example 1:

- name: Display all variables/facts known for a host
  debug:
    var: hostvars[inventory_hostname]
    verbosity: 4

This displays all the variable information for a host that is defined in the inventory file.

Example 2:

- name: Write some content in a file /tmp/foo.txt
  copy:
    dest: /tmp/foo.txt
    content: |
      Good Morning!
      Awesome sunshine today.
    register: display_file_content
- name: Debug display_file_content
    debug:
      var: display_file_content
      verbosity: 2

This registers the content of the copy module output and displays it only when you specify verbosity as 2. For example:

ansible-playbook demo.yaml -vv

Module 5: File

The file module manages the file and its properties.

• It sets attributes of files, symlinks, or directories.
• It also removes files, symlinks, or directories.

Example 1:

- name: Change file ownership, group and permissions
  file:
    path: /etc/foo.conf
    owner: foo
    group: foo
    mode: '0644'

This creates a file named foo.conf and sets the permission to 0644.

Example 2:

- name: Create a directory if it does not exist
  file:
    path: /etc/some_directory
    state: directory
    mode: '0755'

This creates a directory named some_directory and sets the permission to 0755.

Module 6: Lineinfile

The lineinfile module manages lines in a text file.

• It ensures a particular line is in a file or replaces an existing line using a back-referenced regular expression.
• It's primarily useful when you want to change just a single line in a file.

Example 1:

- name: Ensure SELinux is set to enforcing mode
  lineinfile:
    path: /etc/selinux/config
    regexp: '^SELINUX='
    line: SELINUX=enforcing

This sets the value of SELINUX=enforcing.

Example 2:

- name: Add a line to a file if the file does not exist, without passing regexp
  lineinfile:
    path: /etc/resolv.conf
    line: 192.168.1.99 foo.lab.net foo
    create: yes

This adds an entry for the IP and hostname in the resolv.conf file.

Module 7: Git

The git module manages git checkouts of repositories to deploy files or software.

Example 1:

# Example Create git archive from repo
- git:
    repo: https://github.com/ansible/ansible-examples.git
    dest: /src/ansible-examples
    archive: /tmp/ansible-examples.zip

Example 2:

- git:
    repo: https://github.com/ansible/ansible-examples.git
    dest: /src/ansible-examples
    separate_git_dir: /src/ansible-examples.git

This clones a repo with a separate Git directory.

Module 8: Cli_command

The cli_command module, first available in Ansible 2.7, provides a platform-agnostic way of pushing text-based configurations to network devices over the network_cli connection plugin.

Example 1:

- name: commit with comment
  cli_config:
    config: set system host-name foo
    commit_comment: this is a test

This sets the hostname for a switch and exits with a commit message.

Example 2:

- name: configurable backup path
  cli_config:
    config: "{{ lookup('template', 'basic/config.j2') }}"
    backup: yes
    backup_options:
      filename: backup.cfg
      dir_path: /home/user

This backs up a config to a different destination file.

Module 9: Archive

The archive module creates a compressed archive of one or more files. By default, it assumes the compression source exists on the target.

Example 1:

- name: Compress directory /path/to/foo/ into /path/to/foo.tgz
  archive:
    path: /path/to/foo
    dest: /path/to/foo.tgz

Example 2:

- name: Create a bz2 archive of multiple files, rooted at /path
  archive:
    path:
    - /path/to/foo
    - /path/wong/foo
    dest: /path/file.tar.bz2
    format: bz2

Module 10: Command

One of the most basic but useful modules, the command module takes the command name followed by a list of space-delimited arguments.

Example 1:

- name: return motd to registered var
  command: cat /etc/motd
  register: mymotd

Example 2:

- name: Change the working directory to somedir/ and run the command as db_owner if /path/to/database does not exist.
  command: /usr/bin/make_database.sh db_user db_name
  become: yes
  become_user: db_owner
  args:
    chdir: somedir/
    creates: /path/to/database

Conclusion

There are tons of modules available in Ansible, but these ten are the most basic and powerful ones you can use for an automation job. As your requirements change, you can learn about other useful modules by entering ansible-doc <module-name> on the command line or refer to the official documentation.