TripleO Container - Types

In Pike release, TripleO container deployment has been completely redesigned, in a way that it is backward comptible with baremetal deployment and re-using most of the existing parts of TripleO. In this post, I would like to detail the different stages of a container deployment and the associated config files and log files.

With Pike release, most of the OpenStack services are containerized, leaving some of the platform services like OpenvSwitch to be completed with subsequent releases.

Types of Container

As of Pike release all the container running in TripleO are based out of Kolla image format. But we can differentiate the containers on the overcloud node based on their purpose and how they are run.

Service Containers

In case of a service, a container will be running all the time in detached mode with restart policy as always. A typical definition of the a service container is shown below, in which restart is set as always and then detach will be left as default which is true. The entry point for this type of container will be kolla_start which will have the command defined via kolla config file.

outputs:
  role_data:
    description: Role data for the Libvirt service.
    value:
      docker_config:
        step_3:
          nova_virtlogd:
            start_order: 0
            image: {get_param: DockerNovaLibvirtImage}
            net: host
            pid: host
            privileged: true
            restart: always

One-Off Containers

But in some cases where a bootstrap of a service is required, before running the actual service or a post action need to be done after deploying the actual service, a one-off container will be run. It will run only once in a deployment and will exit after the deployment. The significant properties of these types of container detach which should be set as false and the restart property is set to default which is no restart. Instead of the actual entry point of the container image, a custom command will be provided along with this container definition. A sample definition is shown below.

outputs:
  role_data:
    description: Role data for the Libvirt service.
    value:
      docker_config:
        step_4:
          nova_libvirt_init_secret:
            image: {get_param: DockerNovaLibvirtImage}
            privileged: false
            detach: false
            command:
              - /bin/bash
              - -c
              ...