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Using services-config.yaml

When you use the simplified Linux service manager to perform a migration, Migrate to Containers creates a new artifact file, services-config.yaml. Use this file to control application initialization on a deployed container.

For example, after you migrate the container, edit the services-config.yaml file to control application initialization to:

  • Remove applications from the file
  • Add applications to the file
  • Edit the initialization properties of an application

Shown below is an example services-config.yaml file:

version: v1beta1
env:
  - name: KEY1
    value: VALUE1
  - name: KEY2
    value: VALUE2
applications:
    - name: nginx
      type: forking
      envfile: /path/to/file.txt
      env:
        - name: KEY3
          value: VALUE3
      start:
      - cmd: /usr/sbin/nginx -g 'daemon on; master_process on;'
      pidfile: /run/nginx.pid
    - name: ssh@
      type: simple
      start:
      - cmd: /usr/sbin/sshd -i $SSHD_OPTS
        ignore_errors: true
      runtime_directories:
        mode: "0755"
        paths:
          - /run/sshd
        preserve: true
    - name: suitecrm
      type: exec
      start:
      - cmd: /etc/init.d/suitecrm start
      status:
        cmd: /etc/init.d/suitecrm status
    - name: phpsessionclean
      type: oneshot
      start:
        - cmd: /usr/lib/php/sessionclean
      timers:
        - name: phpsessionclean.timer
          on_calendar:
            - cron: 09,39 * * * *
    - name: mariadb
      type: notify
      prestart:
        - cmd: /usr/bin/install -m 755 -o mysql -g root -d /var/run/mysqld
        - cmd: /bin/sh -c "systemctl unset-environment _WSREP_START_POSITION"
        - cmd: /bin/sh -c "[ ! -e /usr/bin/galera_recovery ] && VAR= || VAR=`cd /usr/bin/..; /usr/bin/galera_recovery`; [ $? -eq 0 ] && systemctl set-environment _WSREP_START_POSITION=$VAR || exit 1"
      start:
      - cmd: /usr/sbin/mysqld $MYSQLD_OPTS $_WSREP_NEW_CLUSTER $_WSREP_START_POSITION
      poststart:
        - cmd: /bin/sh -c "systemctl unset-environment _WSREP_START_POSITION"
        - cmd: /etc/mysql/debian-start
      user: mysql
      group: mysql

In this file:

  • env: Specifies environment variables at the global level or at the application level. If you specify the same environment variable at both the global and application levels, then the environment variable at the application level takes precedence.

    • For environment variables set at the global level, use env to specify a name/value pair. Names can contain ASCII letters, digits, and the underscore character. Names cannot start with a digit.

    • For environment variables set at the application level, use env to specify a name/value pair. Or, use envfile to specify the path to a text file containing lines in the form:

      # Comments allowed
      KEY=VALUE

      If the text file contains an environment variable definition that duplicates one specified by env, then the one specified by env takes precedence.

  • applications: Specifies the list of applications to be started when you deploy the container and sets the application's initialization properties.

    • name: Specifies the name of the application.

    • type specifies the type of the application, as one of the following:

      • forking: Run the file specified by start without forking. The service executable is expected to fork. We recommend that you also set pidfile.

      • exec: Fork to run the service. The service is considered started after exec has been called on the executable.

      • simple - Same as exec. A simple service behaves differently from the systemd definition because it waits for both fork and exec instead of for fork.

      • notify: Same as exec except that for systemd the NOTIFY_SOCKET environment variable is not set so sd_notify systemd calls do not work.

      • oneshot: The service is considered started after exec is called on the executable. The status is error if the service exits with an error code not equal to 0.

    • prestart, start, poststart, and status commands for the service.

      To start a service, Migrate to Containers executes the prestart commands (if any), then the start command, and finally the poststart commands (if any). If a command fails, and you have not configured the command to use ignore_errors, then the service is stopped and you see an error message in the service's status.

      The commands used to perform specific operations on the application have the form:

        command-type: 
          cmd: command
          shell: /bin/sh
          ignore_errors: false
          ignore_environment_variables: false

      Where:

      • command-type: Specifies the command type as either prestart, start, poststart, or status.

        For start, you can have a single command unless the type is oneshot.

        If type=forking or type=oneshot, the poststart commands are executed after the start command forks. Otherwise, they are executed immediately after executing the start command.

      • command: Specifies the command to run to perform the operation.

      • shell (Optional): By default, all commands are executed in the /bin/sh shell. You can optionally set shell to /bin/bash.

      • ignore_errors (Optional): If true, an exit code from the command normally considered a failure is recorded, but the command is considered to have succeeded. The default value is false.

        By default, Migrate to Containers sets ignore_errors to true for any systemd executable that includes the "-" prefix.

      • ignore_environment_variables (Optional): If true, environment variable substitution is not applied. The default value is false.

        By default, Migrate to Containers sets ignore_environment_variables to true for any systemd executable that includes the ":" prefix.

    • pidfile: Specifies the pid file containing the process ID of the service which is used to check if the process is still running.

    • chdir: Specifies the working directory of the started process.

    • user: Specifies the user name under which the new process is started.

    • group: Specifies the group name under which the new process is started.

    • timers: Specifies the list of timers of the application. The application will be activated whenever any of the specified timers elapse.

      version: v1beta1
      env: []
      Applications:
      - name: service_name
        type: service_type
        start:
          - cmd: service_exec_command
        timers:
          - name: timer_name
            on_calendar:
              - cron: realtime_time
            on_startup:
              - duration: monotonic_time
            on_service_start:
              - duration: monotonic_time
            on_service_stop:
              - duration: monotonic_time
      
      • name: Specifies the name of the timer.

      • on_calendar: Specifies the list of calendar events for the timer.

        • cron: A specified time using cron format. For example:

          cron: 0 0 * * *
          cron: @daily
          
      • on_startup: Specifies a list of durations (relative to when you deploy your container).

        • duration: A specified time using duration format. For example:
        duration: 30m
        duration: 1sec
        
      • on_service_start: Specifies a list of durations, relative to when your application's status changes to active.

        • duration: A specified time using duration format.
      • on_service_stop: Specifies a list of durations, relative to when your application's status changes to inactive.

        • duration: A specified time using duration format.
    • Use the following properties to specify paths to directories that are created before starting the service:

      • runtime_directories: Specifies the list of paths to directories created in /run/.

      • state_directories: Specifies the list of paths to directories created in /var/lib/.

      • cache_directories: Specifies the list of paths to directories created in /var/cache/.

      • logs_directories: Specifies the list of paths to directories created in /var/log/.

      • configuration_directories: Specifies the list of paths to directories created in /etc/.

      Each of these properties takes the following options:

      • mode: Specifies the file mode. The default is 0755, corresponding to read and execute access for everyone, and write access for the owner.
      • preserve: If false the directory is cleaned up when the service is stopped. The default is true.

Add or remove a service to your services.yaml file

You can add or remove a service from your services.yaml file by manually editing it. Whenever you add a new service, you must populate the following fields:

  • name
  • type
  • start

For more information about the mandatory and optional fields for a service, see the services.yaml definition above.

Add a service

To add a service to your services.yaml file, follow these steps:

  1. Open your services.yaml file in a text editor for modification.

  2. In services.yaml, navigate to the applications attribute:

    version: v1beta1
    env:
     - name: KEY1
     ...
    applications:
    
  3. Add your desired service on the line below the applications attribute starting with the name field, followed by the other mandatory and optional fields appropriate to your application:

    version: v1beta1
    env:
     - name: KEY1
     ...
    applications:
    - name:
      type:
      start:
        - cmd:
      ...
    

    If your services.yaml file already has service definitions under the applications attribute, you can add a new service starting with the name field on the line below the last entry of the previous service:

    version: v1beta1
    env:
     - name: KEY1
     ...
    applications:
    - name:
      type:
      start:
    - name:
      type:
      start:
        ...
    
  4. Save your services.yaml file.

Remove a service

To remove a service from your services.yaml file, follow these steps:

  1. Open your services.yaml file in a text editor for modification.

  2. In services.yaml, navigate to the applications attribute:

    version: v1beta1
    env:
     - name: KEY1
     ...
    applications:
    ...
    
  3. Remove your desired service starting with the name field, followed by the other mandatory and optional fields appropriate to your application. For example:

    Before the service has been removed:

    version: v1beta1
    env:
    - name: KEY1
      ...
    applications:
    - name:
      type:
      start:
        - cmd:
    - name:
      ...
    
    

    After the service has been removed:

    version: v1beta1
    env:
    - name: KEY1
      ...
    applications:
    - name:
      ...
    
  4. Save your services.yaml file.