Tips and Tricks for containerizing services

This document contains a list of tips and tricks that are useful when containerizing an OpenStack service.

Important Notes


Prior to Stein, containerized OpenStack deployments used Docker.

Starting with the Stein release, Docker is no longer part of OpenStack, and Podman has taken its place. The notes here are regarding Stein and later.

Monitoring containers

It’s often useful to monitor the running containers and see what has been executed and what not. The puppet containers are created and removed automatically unless they fail. For all the other containers, it’s enough to monitor the output of the command below:

$ watch -n 0.5 sudo podman ps -a --filter label=managed_by=tripleo_ansible


$ watch -n 0.5 sudo podman ps -a --filter label=managed_by=paunch

Viewing container logs

You can view the output of the main process running in a container by running:

$ sudo podman logs $CONTAINER_ID_OR_NAME

Since the Stein release, standard out and standard error from containers are captured in /var/log/containers/stdouts.

We export traditional logs from containers into the /var/log/containers directory on the host, where you can look at them.

systemd and podman

Throughout this document you’ll find references to direct podman commands for things like restarting services. These are valid and supported methods, but it’s worth noting that services are tied into the systemd management system, which is often the preferred way to operate.

Restarting nova_scheduler for example:

$ sudo systemctl restart tripleo_nova_scheduler

Stopping a container with systemd:

$ sudo systemctl stop tripleo_nova_scheduler

Toggle debug

For services that support reloading their configuration at runtime:

$ sudo podman exec -u root nova_scheduler crudini --set /etc/nova/nova.conf DEFAULT debug true
$ sudo podman kill -s SIGHUP nova_scheduler

Restart the container to turn back the configuration to normal:

$ sudo podman restart nova_scheduler

Otherwise, if the service does not yet support reloading its configuration, it is necessary to change the configuration on the host filesystem and restart the container:

$ sudo crudini --set /var/lib/config-data/puppet-generated/nova/etc/nova/nova.conf DEFAULT debug true
$ sudo podman restart nova_scheduler

Apply the inverse change to restore the default log verbosity:

$ sudo crudini --set /var/lib/config-data/puppet-generated/nova/etc/nova/nova.conf DEFAULT debug false
$ sudo podman restart nova_scheduler

Debugging container failures

The following commands are useful for debugging containers.

  • inspect: This command allows for inspecting the container’s structure and metadata. It provides info about the bind mounts on the container, the container’s labels, the container’s command, etc:

    $ sudo podman inspect $CONTAINER_ID_OR_NAME
  • top: Viewing processes running within a container is trivial with Podman:

    $ sudo podman top $CONTAINER_ID_OR_NAME
  • exec: Running commands on or attaching to a running container is extremely useful to get a better understanding of what’s happening in the container. It’s possible to do so by running the following command:

    $ sudo podman exec -ti $CONTAINER_ID_OR_NAME /bin/bash

    Replace the /bin/bash above with other commands to run oneshot commands. For example:

    $ sudo podman exec -ti mysql mysql -u root -p $PASSWORD

    The above will start a mysql shell on the mysql container.

  • export When the container fails, it’s basically impossible to know what happened. It’s possible to get the logs from docker but those will contain things that were printed on the stdout by the entrypoint. Exporting the filesystem structure from the container will allow for checking other logs files that may not be in the mounted volumes:

    $ sudo podman export $CONTAINER_ID_OR_NAME -o $CONTAINER_ID_OR_NAME.tar

Debugging with tripleo_container_manage Ansible role

The debugging manual for tripleo_container_manage is documented in the role directly.

Debugging with Paunch


During Ussuri cycle, Paunch has been replaced by the tripleo_container_manage Ansible role. Therefore, the following block is deprecated in favor of the new role which contains a Debug manual.

The paunch debug command allows you to perform specific actions on a given container. This can be used to:

  • Run a container with a specific configuration.

  • Dump the configuration of a given container in either json or yaml.

  • Output the docker command line used to start the container.

  • Run a container with any configuration additions you wish such that you can run it with a shell as any user etc.

The configuration options you will likely be interested in include:

--file <file>         YAML or JSON file containing configuration data
--action <name>       Action can be one of: "dump-json", "dump-yaml",
                      "print-cmd", or "run"
--container <name>    Name of the container you wish to manipulate
--interactive         Run container in interactive mode - modifies config
                      and execution of container
--shell               Similar to interactive but drops you into a shell
--user <name>         Start container as the specified user
--overrides <name>    JSON configuration information used to override
                      default config values
--default-runtime     Default runtime for containers. Can be docker or

file is the name of the configuration file to use containing the configuration for the container you wish to use. TripleO creates configuration files for starting containers in /var/lib/tripleo-config/container-startup-config. If you look in this directory you will see a number of files corresponding with the steps in TripleO heat templates. Most of the time, you will likely want to use /var/lib/tripleo-config/container-startup-config/step_4 as it contains most of the final startup configurations for the running containers.

shell, user and interactive are available as shortcuts that modify the configuration to easily allow you to run an interactive session in a given container.

To make sure you get the right container you can use the paunch list command to see what containers are running and which config id they are using. This config id corresponds to which file you will find the container configuration in.

TripleO uses managed_by and config_id labels to help identify the containers it is managing. These can be checked by inspecting the labels section like so:

# podman inspect nova_api | jq '.[0].Config.Labels | "managed_by=\(.managed_by) config_id=\(.config_id)"'
"managed_by=tripleo-Controller config_id=tripleo_step4"

Note that if you wish to replace a currently running container you will want to sudo podman rm -f the running container before starting a new one.

Here is an example of using paunch debug to start a root shell inside the heat api container:

# paunch debug --file /var/lib/tripleo-config/container-startup-config/step_4  --managed-by=tripleo-Controller --config-id=tripleo_step4 --interactive --shell --user root --container nova_api --action run

This will drop you into an interactive session inside the heat api container, starting /bin/bash running as root.

To see how this container is started by TripleO:

# paunch debug --file /var/lib/tripleo-config/container-startup-config/step_4 --managed-by=tripleo-Controller --config-id=tripleo_step4 --container nova_api --action print-cmd

podman run --name nova_api-1jpm5kyv --label config_id=tripleo_step4 --label container_name=nova_api --label managed_by=tripleo-Controller --label config_data={"environment": {"KOLLA_CONFIG_STRATEGY": "COPY_ALWAYS", "TRIPLEO_CONFIG_HASH": "5cbcd2d39667626874f547214d3980ec"}, "healthcheck": {"test": "/openstack/healthcheck"}, "image": "undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp16-openstack-nova-api:16.1_20210726.1", "net": "host", "privileged": false, "restart": "always", "start_order": 2, "user": "root", "volumes": ["/etc/hosts:/etc/hosts:ro", "/etc/localtime:/etc/localtime:ro", "/etc/pki/ca-trust/extracted:/etc/pki/ca-trust/extracted:ro", "/etc/pki/ca-trust/source/anchors:/etc/pki/ca-trust/source/anchors:ro", "/etc/pki/tls/certs/ca-bundle.crt:/etc/pki/tls/certs/ca-bundle.crt:ro", "/etc/pki/tls/certs/", "/etc/pki/tls/cert.pem:/etc/pki/tls/cert.pem:ro", "/dev/log:/dev/log", "/etc/puppet:/etc/puppet:ro", "/var/log/containers/nova:/var/log/nova:z", "/var/log/containers/httpd/nova-api:/var/log/httpd:z", "/var/lib/kolla/config_files/nova_api.json:/var/lib/kolla/config_files/config.json:ro", "/var/lib/config-data/puppet-generated/nova:/var/lib/kolla/config_files/src:ro"]} --conmon-pidfile=/var/run/ --detach=true --env=KOLLA_CONFIG_STRATEGY=COPY_ALWAYS --env=TRIPLEO_CONFIG_HASH=5cbcd2d39667626874f547214d3980ec --net=host --privileged=false --user=root --volume=/etc/hosts:/etc/hosts:ro --volume=/etc/localtime:/etc/localtime:ro --volume=/etc/pki/ca-trust/extracted:/etc/pki/ca-trust/extracted:ro --volume=/etc/pki/ca-trust/source/anchors:/etc/pki/ca-trust/source/anchors:ro --volume=/etc/pki/tls/certs/ca-bundle.crt:/etc/pki/tls/certs/ca-bundle.crt:ro --volume=/etc/pki/tls/certs/ --volume=/etc/pki/tls/cert.pem:/etc/pki/tls/cert.pem:ro --volume=/dev/log:/dev/log --volume=/etc/puppet:/etc/puppet:ro --volume=/var/log/containers/nova:/var/log/nova:z --volume=/var/log/containers/httpd/nova-api:/var/log/httpd:z --volume=/var/lib/kolla/config_files/nova_api.json:/var/lib/kolla/config_files/config.json:ro --volume=/var/lib/config-data/puppet-generated/nova:/var/lib/kolla/config_files/src:ro undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp16-openstack-nova-api:16.1_20210726.1

You can also dump the configuration of a container to a file so you can edit it and rerun it with different a different configuration:

# paunch debug --file /var/lib/tripleo-config/container-startup-config/step_4 --container nova_api --action dump-json > nova_api.json

You can then use nova_api.json as your --file argument after editing it to your liking.

To add configuration elements on the command line you can use the overrides option. In this example I’m adding a health check to the container:

# paunch debug --file nova_api.json --overrides '{"health-cmd": "/usr/bin/curl -f http://localhost:8004/v1/", "health-interval": "30s"}' --container nova_api --managed-by=tripleo-Controller --config-id=tripleo_step4 --action run


The script manages the config file generation and puppet tasks for each service. This also exists in the common directory of tripleo-heat-templates. When writing these tasks, it’s useful to be able to run them manually instead of running them as part of the entire stack. To do so, one can run the script as shown below:

CONFIG=/path/to/task.json /path/to/


Prior to the Train cycle, was called which was located in the docker directory.

The json file must follow the following form:

        "config_image": ...,
        "config_volume": ...,
        "puppet_tags": ...,
        "step_config": ...

Using a more realistic example. Given a puppet_config section like this:

  config_volume: glance_api
  puppet_tags: glance_api_config,glance_api_paste_ini,glance_swift_config,glance_cache_config
  step_config: {get_attr: [GlanceApiPuppetBase, role_data, step_config]}
  config_image: {get_param: DockerGlanceApiConfigImage}

Would generated a json file called /var/lib/container-puppet/container-puppet-tasks2.json that looks like:

        "config_image": "tripleomaster/centos-binary-glance-api:latest",
        "config_volume": "glance_api",
        "puppet_tags": "glance_api_config,glance_api_paste_ini,glance_swift_config,glance_cache_config",
        "step_config": "include ::tripleo::profile::base::glance::api\n"

Setting the path to the above json file as the CONFIG environment variable passed to will create a container using the centos-binary-glance-api:latest image and it and run puppet on a catalog restricted to the given puppet puppet_tags.

As mentioned above, it’s possible to create custom json files and call manually, which makes developing and debugging puppet steps easier. also supports the environment variable SHOW_DIFF, which causes it to print out a docker diff of the container before and after the configuration step has occurred.

By default runs things in parallel. This can make it hard to see the debug output of a given container so there is a PROCESS_COUNT variable that lets you override this. A typical debug run for container-puppet might look like:

SHOW_DIFF=True PROCESS_COUNT=1 CONFIG=glance_api.json ./

Testing a code fix in a container

Let’s assume that we need to test a code patch or an updated package in a container. We will look at a few steps that can be taken to test a fix in a container on an existing deployment.

For example let’s update packages for the mariadb container:

(undercloud) [stack@undercloud ~]$ sudo podman images | grep mariadb    latest     035a8237c376    2 weeks ago    723.5 MB

So container image 035a8237c376 is the one we need to base our work on. Since container images are supposed to be immutable we will base our work off of 035a8237c376 and create a new one:

mkdir -p galera-workaround
cat > galera-workaround/Dockerfile <<EOF
USER root
RUN yum-config-manager --add-repo && yum clean all && rm -rf /var/cache/yum
RUN yum update -y pacemaker pacemaker-remote pcs libqb resource-agents && yum clean all && rm -rf /var/cache/yum
USER mysql

To determine which user is the default one being used in a container you can run docker run -it 035a8237c376 whoami. Then we build the new image and tag it with :workaround1:

docker build --rm -t ~/galera-workaround

Then we push it in our docker registry on the undercloud:

docker push

At this stage we can either point THT to use as the container image by tweaking the necessary environment files and we redeploy the overcloud. If we only want to test a tweaked image, the following steps can be used: First, determine if the containers are managed by pacemaker (those will typically have a :pcmklatest tag) or by paunch. For the paunch-managed containers see Debugging with Paunch. For the pacemaker-managed containers you can (best done on your staging env, as it might be an invasive operation) do the following:

1. `pcs cluster cib cib.xml`
2. Edit the cib.xml with the changes around the bundle you are tweaking
3. `pcs cluster cib-push --config cib.xml`

Testing in CI

When new service containers are added, be sure to update the image names in container-images in the tripleo-common repo. These service images are pulled in and available in the local docker registry that the containers ci job uses.

Packages versions in containers

With the container CI jobs, it can be challenging to find which version of OpenStack runs in the containers. An easy way to find out is to use the logs/undercloud/home/zuul/overcloud_containers.yaml.txt.gz log file and see which tag was deployed.

For example:

- imagename:

So we know the tag is ac82ea9271a4ae3860528eaf8a813da7209e62a6_28eeb6c7. The tag is actually a Delorean hash. You can find out the versions of packages by using this tag. For example, ac82ea9271a4ae3860528eaf8a813da7209e62a6_28eeb6c7 tag, is in fact using this Delorean repository.