Primer python-tripleoclient and tripleo-common

This document gives an overview of how python-tripleoclient provides the cli interface for TripleO. In particular it focuses on two key aspects of TripleO commands: where they are defined and how they (very basically) work.

Whilst python-tripleoclient provides the CLI for TripleO, it is in tripleo-common that the logic behind a given command resides. So interfacing with OpenStack services such as Heat, Nova or Mistral typically happens in tripleo-common.

For this primer we will use a specific example command but the same applies to any TripleO cli command to be found in the TripleO documentation or in any local deployment (or even in TripleO CI) logfiles.

The example used here is:

openstack overcloud container image build

This command is used to build the container images listed in the tripleo-common file overcloud_containers.yaml using Kolla.

See the Building Containers Deploy Guide for more information on how to use this command as an operator.

One of the TripleO CI jobs that executes this command is the tripleo-build-containers-centos-7 job. This job invokes the overcloud container image build command in the template:

openstack overcloud container image build \
--config-file $TRIPLEO_COMMON_PATH/container-images/overcloud_containers.yaml \
--kolla-config-file {{ workspace }}/kolla-build.conf \

The relevance of showing this is simply to serve as an example in the following sections. First we see how to identify where in the tripleoclient code a given command is defined, and then how the command works, highlighting a recurring pattern common to all TripleO commands.

TripleO commands: where

Luckily the location of all TripleO commands is given in the list of entry_points in the python-tripleoclient setup.cfg file. Each key=value pair has a key derived from the TripleO command. Taking the command, omit the initial openstack and link subcommands with underscore instead of whitespace. That is, for the openstack overcloud container image build command the equivalent entry is overcloud_container_image_build:

openstack.cli.extension =
    tripleoclient = tripleoclient.plugin

openstack.tripleoclient.v1 =
    overcloud_container_image_build = tripleoclient.v1.container_image:BuildImage

The value in each key=value pair provides us with the file and class name used in the tripleoclient namespace for this command. For overcloud_container_image_build we have tripleoclient.v1.container_image:BuildImage, which means this command is defined in a class called BuildImage inside the tripleoclient/v1/ file.

TripleO commands: how

Obviously each TripleO command ‘works’ differently in that they are doing different things - deploy vs upgrade the undercloud vs overcloud etc. However there is at least one commonality which we highlight in this section. Each TripleO command class defines a get_parser function and a take_action function.

The get_parser is where all command line arguments are defined and take_action is where tripleo-common is invoked to perform the task at hand, building container images in this case.

Looking inside the BuildImage class we find:

def get_parser(self, prog_name):
        metavar='<yaml config file>',
        help=_("YAML config file specifying the images to build. May be "
               "specified multiple times. Order is preserved, and later "
               "files will override some options in previous files. "
               "Other options will append. If not specified, the default "
               "set of containers will be built."),

Here we can see where the two arguments shown in the introduction above are defined: –config-file and –kolla-config-file. You can see the default values and all other attributes for each of the command parameters there.

Finally we can look for the take_action function to learn more about how the command actually ‘works’. Typically the take_action function will have some validation of the provided arguments before calling out to tripleo-common to actually ‘do’ the work (build container images in this case):

from tripleo_common.image import kolla_builder
def take_action(self, parsed_args):
        builder = kolla_builder.KollaImageBuilder(parsed_args.config_files)
        result = builder.build_images(kolla_config_files,

Here we can see the actual image build is done by the kolla_builder.KollaImageBuilder class build_images function. Looking in tripleo-common we can follow that python namespace to find the definition of build_images in the tripleo_common/image/ file:

def build_images(self, kolla_config_files=None, excludes=[],
             template_only=False, kolla_tmp_dir=None):
    cmd = ['kolla-build']