Red Hat Enterprise Linux Automation with Ansible

Procedure 4.2. Instructions

1. On workstation.lab.example.com, open a new terminal and change to the /home/student/control-handlers project directory.

   [student@workstation ~]$ cd ~/control-handlers
   [student@workstation control-handlers]$

2. In that directory, use a text editor to edit the configure_db.yml playbook file. This playbook installs and configures a database server. When the database server configuration changes, the playbook triggers a restart of the database service and configures the database administrative password.

   1. Using a text editor, review the configure_db.yml playbook. It begins with the initialization of some variables:

      ---
      - name: MariaDB server is installed
        hosts: databases
        vars:
          db_packages: 
            - mariadb-server
            - python3-PyMySQL
          db_service: mariadb 
          resources_url: http://materials.example.com/labs/control-handlers 
          config_file_url: "{{ resources_url }}/my.cnf.standard" 
          config_file_dst: /etc/my.cnf 
        tasks:

      	db_packages defines the name of the packages to install for the database service.
      	db_service defines the name of the database service.
      	resources_url represents the URL for the resource directory where remote configuration files are located.
      	config_file_url represents the URL of the database configuration file to install.
      	config_file_dst: Location of the installed configuration file on the managed hosts.

   2. In the configure_db.yml file, define a task that uses the yum module to install the required database packages as defined by the db_packages variable. If the task changes the system, the database was not installed, and you need to notify the set db password handler to set your initial database user and password. Remember that the handler task, if it is notified, will not run until every task in the tasks section has run.

      The task should read as follows:

        tasks:
          - name: "{{ db_packages }} packages are installed"
            yum:
              name: "{{ db_packages }}"
              state: present
            notify:
              - set db password

   3. 2.3)

      Add a task to start and enable the database service. The task should read as follows:

          - name: Make sure the database service is running
            service:
              name: "{{ db_service }}"
              state: started
              enabled: true

   4. Add a task to download my.cnf.standard to /etc/my.cnf on the managed host, using the get_url module. Add a condition that notifies the restart db service handler to restart the database service after a configuration file change. The task should read:

          - name: The {{ config_file_dst }} file has been installed
            get_url:
              url: "{{ config_file_url }}"
              dest: "{{ config_file_dst }}"
              owner: mysql
              group: mysql
              force: yes
            notify:
              - restart db service

   5. Add the handlers keyword to define the start of the handler tasks. Define the first handler, restart db service, which restarts the mariadb service. It should read as follows:

        handlers:
          - name: restart db service
            service:
              name: "{{ db_service }}"
              state: restarted

   6. Define the second handler, set db password, which sets the administrative password for the database service. The handler uses the mysql_user module to perform the command. The handler should read as follows:

          - name: set db password
            mysql_user:
              name: root
              password: redhat

      When completed, the playbook should appear as follows:

      ---
      - name: MariaDB server is installed
        hosts: databases
        vars:
          db_packages:
            - mariadb-server
            - python3-PyMySQL
          db_service: mariadb
          resources_url: http://materials.example.com/labs/control-handlers
          config_file_url: "{{ resources_url }}/my.cnf.standard"
          config_file_dst: /etc/my.cnf
        tasks:
          - name: "{{ db_packages }} packages are installed"
            yum:
              name: "{{ db_packages }}"
              state: present
            notify:
              - set db password
      
          - name: Make sure the database service is running
            service:
              name: "{{ db_service }}"
              state: started
              enabled: true
      
          - name: The {{ config_file_dst }} file has been installed
            get_url:
              url: "{{ config_file_url }}"
              dest: "{{ config_file_dst }}"
              owner: mysql
              group: mysql
              force: yes
            notify:
              - restart db service
      
        handlers:
          - name: restart db service
            service:
              name: "{{ db_service }}"
              state: restarted
      
          - name: set db password
            mysql_user:
              name: root
              password: redhat

3. Before running the playbook, verify that its syntax is correct by running ansible-playbook with the --syntax-check option. If it reports any errors, correct them before moving to the next step. You should see output similar to the following:

   [student@workstation control-handlers]$ ansible-playbook configure_db.yml \
   > --syntax-check
   
   playbook: configure_db.yml

4. Run the configure_db.yml playbook. The output shows that the handlers are being executed.

   [student@workstation control-handlers]$ ansible-playbook configure_db.yml
   
   PLAY [Installing MariaDB server] *********************************************
   
   TASK [Gathering Facts] *******************************************************
   ok: [servera.lab.example.com]
   
   TASK [['mariadb-server', 'python3-PyMySQL'] packages are installed] **********
   changed: [servera.lab.example.com]
   
   TASK [Make sure the database service is running] *****************************
   changed: [servera.lab.example.com]
   
   TASK [The /etc/my.cnf file has been installed] *******************************
   changed: [servera.lab.example.com]
   
   RUNNING HANDLER [restart db service] *****************************************
   changed: [servera.lab.example.com]
   
   RUNNING HANDLER [set db password] ********************************************
   changed: [servera.lab.example.com]
   
   PLAY RECAP *******************************************************************
   servera.lab.example.com    : ok=6    changed=5    unreachable=0    failed=0

5. Run the playbook again.

   [student@workstation control-handlers]$ ansible-playbook configure_db.yml
   
   PLAY [Installing MariaDB server] *********************************************
   
   TASK [Gathering Facts] *******************************************************
   ok: [servera.lab.example.com]
   
   TASK [['mariadb-server', 'python3-PyMySQL'] packages are installed] **********
   ok: [servera.lab.example.com]
   
   TASK [Make sure the database service is running] *****************************
   ok: [servera.lab.example.com]
   
   TASK [The /etc/my.cnf file has been installed] *******************************
   ok: [servera.lab.example.com]
   
   PLAY RECAP *******************************************************************
   servera.lab.example.com    : ok=4    changed=0    unreachable=0    failed=0

   This time the handlers are skipped. In the event that the remote configuration file is changed in the future, executing the playbook would trigger the restart db service handler but not the set db password handler.