Tips and Tricks for containerizing services =========================================== This document contains a list of tips and tricks that are useful when containerizing an OpenStack service. 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 docker ps -a --filter label=managed_by=docker-cmd .. _debug-containers: Viewing container logs ---------------------- You can view the output of the main process running in a container by running:: $ docker logs $CONTAINER_ID_OR_NAME Ideally all containerized processes would log everything to stdout/stderr and the above command would suffice. Not all services are quite there yet, so we export traditional logs from containers into the `/var/log/containers` directory on the host, where you can look at them. .. _toggle_debug: Toggle debug ------------ For services that support `reloading their configuration at runtime`_:: $ sudo docker exec -u root nova_scheduler crudini --set /etc/nova/nova.conf DEFAULT debug true $ sudo docker kill -s SIGHUP nova_scheduler .. _reloading their configuration at runtime: https://storyboard.openstack.org/#!/story/2001545 Restart the container to turn back the configuration to normal:: $ sudo docker 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 docker 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 docker 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:: $ docker inspect $CONTAINER_ID_OR_NAME There's no shortcut for *rebuilding* the command that was used to run the container but, it's possible to do so by using the `docker inspect` command and the format parameter:: $ docker inspect --format='{{range .Config.Env}} -e "{{.}}" {{end}} {{range .Mounts}} -v {{.Source}}:{{.Destination}}{{if .Mode}}:{{.Mode}}{{end}}{{end}} -ti {{.Config.Image}}' $CONTAINER_ID_OR_NAME Copy the output from the command above and append it to the one below, which will run the same container with a random name and remove it as soon as the execution exits:: $ docker run --rm $OUTPUT_FROM_PREVIOUS_COMMAND /bin/bash * **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:: $ docker exec -ti $CONTAINER_ID_OR_NAME /bin/bash Replace the `/bin/bash` above with other commands to run oneshot commands. For example:: $ docker 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:: $ docker export $CONTAINER_ID_OR_NAME | tar -C /tmp/$CONTAINER_ID_OR_NAME -xvf - Debugging with Paunch --------------------- 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 YAML or JSON file containing configuration data --action Action can be one of: "dump-json", "dump-yaml", "print-cmd", or "run" --container 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 Start container as the specified user --overrides JSON configuration information used to override default config values --default-runtime Default runtime for containers. Can be docker or podman. ``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/``. 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/hashed-docker-container-startup-config-step_4.json`` 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. Note that if you wish to replace a currently running container you will want to ``docker rm`` 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/hashed-docker-container-startup-config-step_4.json --interactive --shell --user root --container heat_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/hashed-docker-container-startup-config-step_4.json --container heat_api --action print-cmd docker run --name heat_api-t7a00bfz --detach=true --env=KOLLA_CONFIG_STRATEGY=COPY_ALWAYS --env=TRIPLEO_CONFIG_HASH=b3154865d1f722ace643ffbab206bf91 --net=host --privileged=false --restart=always --user=root --volume=/etc/hosts:/etc/hosts:ro --volume=/etc/localtime:/etc/localtime:ro --volume=/etc/puppet:/etc/puppet:ro --volume=/etc/pki/ca-trust/extracted:/etc/pki/ca-trust/extracted:ro --volume=/etc/pki/tls/certs/ca-bundle.crt:/etc/pki/tls/certs/ca-bundle.crt:ro --volume=/etc/pki/tls/certs/ca-bundle.trust.crt:/etc/pki/tls/certs/ca-bundle.trust.crt:ro --volume=/etc/pki/tls/cert.pem:/etc/pki/tls/cert.pem:ro --volume=/dev/log:/dev/log --volume=/etc/ssh/ssh_known_hosts:/etc/ssh/ssh_known_hosts:ro --volume=/var/lib/kolla/config_files/heat_api.json:/var/lib/kolla/config_files/config.json:ro --volume=/var/lib/config-data/heat_api/etc/heat/:/etc/heat/:ro --volume=/var/lib/config-data/heat_api/etc/httpd/conf/:/etc/httpd/conf/:ro --volume=/var/lib/config-data/heat_api/etc/httpd/conf.d/:/etc/httpd/conf.d/:ro --volume=/var/lib/config-data/heat_api/etc/httpd/conf.modules.d/:/etc/httpd/conf.modules.d/:ro --volume=/var/lib/config-data/heat_api/var/www/:/var/www/:ro --volume=/var/log/containers/heat:/var/log/heat 192.168.24.1:8787/tripleomaster/centos-binary-heat-api:latest 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/hashed-docker-container-startup-config-step_4.json --container heat_api --action dump-json > heat_api.json You can then use ``heat_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 /var/lib/tripleo-config/hashed-docker-container-startup-config-step_4.json --overrides '{"health-cmd": "/usr/bin/curl -f http://localhost:8004/v1/", "health-interval": "30s"}' --container heat_api --action run 172ed68eb44ab20551a70a3e33c90a02014f530e42cd7b30255da4577c8ed80c Debugging docker-puppet.py -------------------------- The :ref:`docker-puppet.py` script manages the config file generation and puppet tasks for each service. This also exists in the `docker` 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/docker-puppet.py 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:: puppet_config: 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/docker-puppet/docker-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 `docker-puppet.py` 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 `docker-puppet.py` manually, which makes developing and debugging puppet steps easier. `docker-puppet.py` 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 `docker-puppet.py` 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 docker-puppet might look like:: SHOW_DIFF=True PROCESS_COUNT=1 CONFIG=glance_api.json ./docker-puppet.py 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 ~]$ docker images | grep mariadb 192.168.24.1:8787/tripleomaster/centos-binary-mariadb latest 035a8237c376 2 weeks ago 723.5 MB So docker image `035a8237c376` is the one we need to base our work on. Since docker 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 <