Ansible Modules

Ansible Service Module: Manage Services

The service module in Ansible comes in handy for managing services across a variety of platforms.

The service module in Ansible provides an easy way to manage system services across different environments. It interacts with the service management tools available on the target system.

These tools are usually different, for example, Linux/Unix init systems such as systemd, BSD init, launchd on macOS, Solaris SMF, and upstart.

However, the service module abstracts the differences between various service management tools, thus providing a unified way to manage services.

Service module parameters

The service module has several different parameters, the most common of which are:

name: the name of the service
enabled: defined if the service must start when the machine boots
pattern: if the status command does not work, this parameter allows you to define whether a service is operational or not
sleep: during the action restarted defines the tempo between stop and start
state: action on the service: started, stopped, restarted or reloaded (in case of modification to a configuration file)

Service module use cases

Service module can be used to run, stop, restart, or reload services as required, helping to automate and standardize the management of your infrastructure. Following is a simple playbook for starting nginx:

---
- name: Manage Nginx service
  hosts: webservers
  tasks:
    - name: Ensure Nginx is running and enabled at boot
      ansible.builtin.service:
        name: nginx
        state: started
        enabled: yes

Similarly, by changing the state parameter, you can stop and restart services. However, use of the service module is not limited to starting and stopping services. Following is an example playbook for installing and configuring nginx (simplified):

---
  - name: manage services
    hosts: all
    become: true
    tasks:
      - name: Installing nginx
        package:
          - name:
            - nginx
      - name: nginx configuration
        template:
          src:nginx.conf.j2
          dest: /etc/nginx/nginx.conf
          owner:root
          group:root
          mode: 0644
      - name: Reloading the conf
        service:
          name: nginx
          state: reloaded
      - name: Verification nginx is started
        service:
          name: nginx
          state:started
          enabled: true

This is a simple example to use the service module but it has certain limitations. One such limit is that our playbook will always reload the nginx service, even if the configuration has not changed. One way to avoid this is to use handlers.

Using handlers to refine Service

Handlers allow you to launch an action if a task has made a modification to the system (status changed). Ansible allows you to trigger events after a task has passed handlers status. Additionally, although multiple tasks may require the same action, the action in question will only be launched after all task blocks have been executed.

Our playbook, therefore becomes:

---
  - name: manage services
    hosts: all
    become: true
    tasks:
      - name: nginx configuration
        template:
          src:nginx.conf.j2
          dest: /etc/nginx/nginx.conf
          owner:root
          group:root
          mode: 0644
        notify:
          - reload nginx
      - name: Verification nginx is started
        service:
          name: nginx
          state:started
          enabled: true

    handlers:
      - name: reload nginx
        service:
          name: nginx
          state: reloaded

As with the package module, there are modules specific to each type of initialization system that have more options: systemd and sysvinit.

Get information about a service: service_facts

Ansible provides a module service_facts allowing you to obtain lots of information about a service.

This module does not take any parameters. On the other hand, it requires that gather_facts are not disabled.

For example, I would like to open ports 80 and 443 only if the firewall service is active. Our playbook becomes:

---
  - name: manage services
    hosts: all
    become: true
    tasks:
      - name: nginx configuration
        template:
          src:nginx.conf.j2
          dest: /etc/nginx/nginx.conf
          owner:root
          group:root
          mode: 0644
        notify:
          - reload nginx
      - name: Gets information about a service
        service_facts:
      - name:debug
        debug:
          var: ansible_facts.services["firewalld.service"]

    handlers:
      - name: reload nginx
        service:
          name: nginx
          state: reloaded

Services is added to the variable ansible_factsand contains the list of all services installed on the machine. So if you want to access the firewalld service, you will have to indicate ansible_facts.services["firewalld.service"].

TASK [debug] *********************************************************************************************
 ok: [host1] => { 
 "firewalld.service": 
 { "name": "firewalld.service", 
 "source": "systemd", 
 "state": "running", 
 "status": "enabled" 
 } 
  }

For example, I could add a task which is only launched if the firewalld service is in its status enabled:

---
  - name: manage services
    hosts: all
    become: true
    tasks:
      - name: nginx configuration
        template:
          src:nginx.conf.j2
          dest: /etc/nginx/nginx.conf
          owner:root
          group:root
          mode: 0644
        notify:
          - reload nginx
      - name: Gets information about a service
        service_facts:
      - name: authorizes the https flow
        ansible.posix.firewalld:
          service: https
          permanent: yes
          state:enabled
        when: ansible_facts.services["firewalld.service"].status == "enabled"

    handlers:
      - name: reload nginx
        service:
          name: nginx
          state: reloaded

Final Words

The service module in Ansible is a powerful tool for managing system services, when used with other modules it provides a high level of control and automation while ensuring consistency across different environments.

If you are new to Ansible and want to learn it from scratch, our Ansible tutorial series will be of great help. It's written for RHCE exam but it helps you the same whether you are preparing for the exam or not.