Container Image Preparation

This documentation explains how to instruct container image preparation to do different preparation tasks.

Choosing an image registry strategy

Container images need to be pulled from an image registry which is reliably available to overcloud nodes. The three common options to serve images are to use the default registry, the registry available on the undercloud, or an independently managed registry. During deployment the environment parameter ContainerImagePrepare is used to specify any desired behaviour, including:

  • Where to pull images from
  • Optionally, which local repository to push images to
  • How to discover the lasted versioned tag for each image

In the following examples, the parameter ContainerImagePrepare will be specified in its own file containers-prepare-parameter.yaml.

Default registry

By default the images will be pulled from a remote registry namespace such as docker.io/tripleomaster. This is fine for development or POC clouds but is not appropriate for production clouds due to the transfer of large amounts of duplicate image data over a potentially unreliable internet connection.

During deployment with this default, any heat parameters which refer to required container images will be populated with a value pointing at the default registry, with a tag representing the latest image version.

To generate the containers-prepare-parameter.yaml containing these defaults, run this command:

openstack tripleo container image prepare default \
  --output-env-file containers-prepare-parameter.yaml

This will generate a file containing a ContainerImagePrepare similar to the following:

parameter_defaults:
  ContainerImagePrepare:
  - set:
      ceph_image: daemon
      ceph_namespace: docker.io/ceph
      ceph_tag: v3.0.3-stable-3.0-luminous-centos-7-x86_64
      name_prefix: centos-binary-
      name_suffix: ''
      namespace: docker.io/tripleomaster
      neutron_driver: null
      tag: current-tripleo
    tag_from_label: rdo_version

During deployment, this will lookup images in docker.io/tripleomaster tagged with current-tripleo and discover a versioned tag by looking up the label rdo_version. This will result in the heat image parameters in the plan being set with appropriate values, such as:

DockerNeutronMetadataImage: docker.io/tripleomaster/centos-binary-neutron-metadata-agent:35414701c176a6288fc2ad141dad0f73624dcb94_43527485
DockerNovaApiImage: docker.io/tripleomaster/centos-binary-nova-api:35414701c176a6288fc2ad141dad0f73624dcb94_43527485

Note

The tag is actually a Delorean hash. You can find out the versions of packages by using this tag. For example, 35414701c176a6288fc2ad141dad0f73624dcb94_43527485 tag, is in fact using this Delorean repository.

Undercloud registry

As part of the undercloud install, an image registry is configured on port 8787. This can be used to increase reliability of image pulls, and minimise overall network transfers. The undercloud registry can be used by generating the following containers-prepare-parameter.yaml file:

openstack tripleo container image prepare default \
  --local-push-destination \
  --output-env-file containers-prepare-parameter.yaml

This will generate a file containing a ContainerImagePrepare similar to the following:

parameter_defaults:
  ContainerImagePrepare:
  - push_destination: true
    set:
      ceph_image: daemon
      ceph_namespace: docker.io/ceph
      ceph_tag: v3.0.3-stable-3.0-luminous-centos-7-x86_64
      name_prefix: centos-binary-
      name_suffix: ''
      namespace: docker.io/tripleomaster
      neutron_driver: null
      tag: current-tripleo
    tag_from_label: rdo_version

This is identical to the default registry, except for the push_destination: true entry which indicates that the address of the local undercloud registry will be discovered at upload time.

By specifying a push_destination value such as 192.168.24.1:8787, during deployment all images will be pulled from the remote registry then pushed to the specified registry. The resulting image parameters will also be modified to refer to the images in push_destination instead of namespace.

Running container image prepare

The prepare operations are run at the following times:

  1. During undercloud install when undercloud.conf has container_images_file=$HOME/containers-prepare-parameter.yaml (see Installing the Undercloud)
  2. During overcloud deploy when a ContainerImagePrepare parameter is provided by including the argument -e $HOME/containers-prepare-parameter.yaml (see Deploying the containerized Overcloud)
  3. Any other time when openstack tripleo container image prepare is run

Options available in heat parameter ContainerImagePrepare

To do something different to the above two registry scenarios, your custom environment can set the value of the ContainerImagePrepare heat parameter to result in any desired registry and image scenario.

Discovering versioned tags with tag_from_label

If you want these parameters to have the actual tag current-tripleo instead of the discovered tag (in this case the Delorean hash, 35414701c176a6288fc2ad141dad0f73624dcb94_43527485 ) then the tag_from_label entry can be omitted.

Likewise, if all images should be deployed with a different tag, the value of tag can be set to the desired tag.

Some build pipelines have a versioned tag which can only be discovered via a combination of labels. For this case, a template format can be specified instead:

tag_from_label: {version}-{release}

Copying images with push_destination

By specifying a push_destination, the required images will be copied from namespace to this registry, for example:

ContainerImagePrepare:
- push_destination: 192.168.24.1:8787
  set:
    namespace: docker.io/tripleomaster
    ...

This will result in images being copied from docker.io/tripleomaster to 192.168.24.1:8787/tripleomaster and heat parameters set with values such as:

DockerNeutronMetadataImage: 192.168.24.1:8787/tripleomaster/centos-binary-neutron-metadata-agent:35414701c176a6288fc2ad141dad0f73624dcb94_43527485
DockerNovaApiImage: 192.168.24.1:8787/tripleomaster/centos-binary-nova-api:35414701c176a6288fc2ad141dad0f73624dcb94_43527485

Note

Use the IP address of your undercloud, which you previously set with the local_ip parameter in your undercloud.conf file. For these example commands, the address is assumed to be 192.168.24.1:8787.

By setting different values for namespace and push_destination any alternative registry strategy can be specified.

Ceph and other set options

The options ceph_namespace, ceph_image, and ceph_tag are similar to namespace and tag but they specify the values for the ceph image. It will often come from a different registry, and have a different versioned tag policy.

The values in the set map are used when evaluating the file /usr/share/openstack-tripleo-common/container-images/overcloud_containers.yaml.j2 as a Jinja2 template. This file contains the list of every container image and how it relates to TripleO services and heat parameters.

Layering image preparation entries

Since the value of ContainerImagePrepare is a list, multiple entries can be specified, and later entries will overwrite any earlier ones. Consider the following:

ContainerImagePrepare:
- tag_from_label: rdo_version
  push_destination: true
  excludes:
  - nova-api
  set:
    namespace: docker.io/tripleomaster
    name_prefix: centos-binary-
    name_suffix: ''
    tag: current-tripleo
- push_destination: true
  includes:
  - nova-api
  set:
    namespace: mylocal
    tag: myhotfix

This will result in the following heat parameters which shows a locally built <build_container_images> and tagged centos-binary-nova-api being used for DockerNovaApiImage:

DockerNeutronMetadataImage: 192.168.24.1:8787/tripleomaster/centos-binary-neutron-metadata-agent:35414701c176a6288fc2ad141dad0f73624dcb94_43527485
DockerNovaApiImage: 192.168.24.1:8787/mylocal/centos-binary-nova-api:myhotfix

The includes and excludes entries can control the resulting image list in addition to the filtering which is determined by roles and containerized services in the plan. includes matches take precedence over excludes matches, followed by role/service filtering. The image name must contain the value within it to be considered a match.

Modifying images during prepare

It is possible to modify images during prepare to make any required changes, then immediately deploy with those changes. The use-cases for modifying images include:

  • As part of a Continuous Integration pipeline where images are modified with the changes being tested before deployment
  • As part of a development workflow where local changes need to be deployed for testing and development
  • When changes need to be deployed but are not available through an image build pipeline (proprietry addons, emergency fixes)

The modification is done by invoking an ansible role on each image which needs to be modified. The role takes a source image, makes the requested changes, then tags the result. The prepare can then push the image and set the heat parameters to refer to the modified image.

The ansible role tripleo-modify-image conforms with the required role interface, and provides the required behaviour for the modify use-cases. Modification is controlled via modify-specific keys in the ContainerImagePrepare parameter:

  • modify_role specifies what ansible role to invoke for each image to modify.
  • modify_append_tag is used to append to the end of the source image tag. This makes it obvious that the resulting image has been modified. It is also used to skip modification if the push_destination registry already has that image, so it is recommended to change modify_append_tag whenever the image must be modified.
  • modify_vars is a dictionary of ansible variables to pass to the role.

The different use-cases handled by role tripleo-modify-image are selected by setting the tasks_from variable to the required file in that role. For all of the following examples, see the documentation for the role tripleo-modify-image for the other variables supported by that tasks_from.

While developing and testing the ContainerImagePrepare entries which modify images, it is recommended to run prepare on its own to confirm it is being modified as expected:

sudo openstack tripleo container image prepare \
  -e ~/containers-prepare-parameter.yaml

Updating existing packages

The following entries will result in all packages being updated in the images, but using the undercloud host’s yum repository configuration:

ContainerImagePrepare:
- push_destination: true
  ...
  modify_role: tripleo-modify-image
  modify_append_tag: "-updated"
  modify_vars:
    tasks_from: yum_update.yml
    compare_host_packages: true
    yum_repos_dir_path: /etc/yum.repos.d
  ...

Install RPM files

It is possible to install a directory of RPM files, which is useful for installing hotfixes, local package builds, or any package which is not available through a package repository. For example the following would install some hotfix packages only in the centos-binary-nova-compute image:

ContainerImagePrepare:
- push_destination: true
  ...
  includes:
  - nova-compute
  modify_role: tripleo-modify-image
  modify_append_tag: "-hotfix"
  modify_vars:
    tasks_from: rpm_install.yml
    rpms_path: /home/stack/nova-hotfix-pkgs
  ...

Modify with custom Dockerfile

For maximum flexibility, it is possible to specify a directory containing a Dockerfile to make the required changes. When the role is invoked, a Dockerfile.modified is generated which changes the FROM directive and adds extra LABEL directives. The following example runs the custom Dockerfile on the centos-binary-nova-compute image:

ContainerImagePrepare:
- push_destination: true
  ...
  includes:
  - nova-compute
  modify_role: tripleo-modify-image
  modify_append_tag: "-hotfix"
  modify_vars:
    tasks_from: modify_image.yml
    modify_dir_path: /home/stack/nova-custom
  ...

An example /home/stack/nova-custom/Dockerfile follows. Note that after any USER root directives have been run, it is necessary to switch back to the original image default user:

FROM docker.io/tripleomaster/centos-binary-nova-compute:latest

USER root

COPY customize.sh /tmp/
RUN /tmp/customize.sh

USER "nova"