Building Container Images

The kolla-build command is responsible for building docker images.


When developing Kolla it can be useful to build images using files located in a local copy of Kolla. Use the tools/ script instead of kolla-build command in all below instructions.

Generating kolla-build.conf

Install tox and generate the build configuration. The build configuration is designed to hold advanced customizations when building containers.

Create kolla-build.conf using the following steps.

pip install tox
tox -e genconfig

The location of the generated configuration file is etc/kolla/kolla-build.conf, it can also be copied to /etc/kolla. The default location is one of /etc/kolla/kolla-build.conf or etc/kolla/kolla-build.conf.


In general, images are built like this:


By default, the above command would build all images based on CentOS image.

The operator can change the base distro with the -b option:

kolla-build -b ubuntu

There are following distros available for building images:

  • fedora
  • centos
  • oraclelinux
  • ubuntu


Fedora images are deprecated since Newton and will be removed in the future.

To push the image after building, add --push:

kolla-build --push

It is possible to build only a subset of images by specifying them on the command line:

kolla-build keystone

In this case, the build script builds all images which name contains the keystone string along with their dependencies.

Multiple names may be specified on the command line:

kolla-build keystone nova

kolla-build uses kolla as default Docker namespace. This is controlled with the -n command line option. To push images to a dockerhub repository named mykollarepo:

kolla-build -n mykollarepo --push

To push images to a local registry, use --registry flag:

kolla-build --registry --push

To trigger the build script to pull images from a local registry, the Docker configuration needs to be modified. See Docker Insecure Registry Config.

The build configuration can be customized using a config file, the default location being one of /etc/kolla/kolla-build.conf or etc/kolla/kolla-build.conf. This file can be generated using the following command:

tox -e genconfig

Build OpenStack from source

When building images, there are two methods of the OpenStack install. One is binary. Another is source. The binary means that OpenStack will be installed from apt/yum. And the source means that OpenStack will be installed from source code. The default method of the OpenStack install is binary. It can be changed to source using the -t option:

kolla-build -t source

The locations of OpenStack source code are written in etc/kolla/kolla-build.conf. Now the source type supports url, git, and local. The location of the local source type can point to either a directory containing the source code or to a tarball of the source. The local source type permits to make the best use of the docker cache.

etc/kolla/kolla-build.conf looks like:

type = url
location =

type = git
location =
reference = stable/mitaka

type = local
location = /home/kolla/src/heat

type = local
location = /tmp/ironic.tar.gz

To build RHEL containers, it is necessary to use the -i (include header) feature to include registration with RHN of the container runtime operating system. To obtain a RHN username/password/pool id, contact Red Hat.

First create a file called rhel-include:

RUN subscription-manager register --user=<user-name> --password=<password> \
&& subscription-manager attach --pool <pool-id>

Then build RHEL containers:

kolla-build -b rhel -i ./rhel-include

Dockerfile Customisation

As of the Newton release, the kolla-build tool provides a Jinja2 based mechanism which allows operators to customise the Dockerfiles used to generate Kolla images.

This offers a lot of flexibility on how images are built, e.g. installing extra packages as part of the build, tweaking settings, installing plugins, and numerous other capabilities. Some of these examples are described in more detail below.

Generic Customisation

Anywhere the line {% block ... %} appears may be modified. The Kolla community have added blocks throughout the Dockerfiles where we think they will be useful, however, operators are free to submit more if the ones provided are inadequate.

The following is an example of how an operator would modify the setup steps within the Horizon Dockerfile.

First, create a file to contain the customisations, e.g. template-overrides.j2. In this place the following:

{% extends parent_template %}

# Horizon
{% block horizon_redhat_binary_setup %}
RUN useradd --user-group myuser
{% endblock %}

Then rebuild the horizon image, passing the --template-override argument:

kolla-build --template-override template-overrides.j2 horizon


The above example will replace all contents from the original block. Hence in many cases one may want to copy the original contents of the block before making changes.

More specific functionality such as removing/appending entries is available for packages, described in the next section.

Package Customisation

Packages installed as part of a container build can be overridden, appended to, and deleted. Taking the Horizon example, the following packages are installed as part of a binary install type build:

  • openstack-dashboard
  • httpd
  • mod_wsgi
  • gettext

To add a package to this list, say, iproute, first create a file, e.g. template-overrides.j2. In this place the following:

{% extends parent_template %}

# Horizon
{% set horizon_packages_append = ['iproute'] %}

Then rebuild the horizon image, passing the --template-override argument:

kolla-build –template-override template-overrides.j2 horizon

Alternatively template_override can be set in kolla-build.conf.

The append suffix in the above example carries special significance. It indicates the operation taken on the package list. The following is a complete list of operations available:

Replace the default packages with a custom list.
Add a package to the default list.
Remove a package from the default list.

Using a different base image

Base-image can be specified by argument --base-image. For example:

kolla-build --base-image --base rhel

Plugin Functionality

The Dockerfile customisation mechanism is also useful for adding/installing plugins to services. An example of this is Neutron’s third party L2 drivers.

The bottom of each Dockerfile contains two blocks, image_name_footer, and footer. The image_name_footer is intended for image specific modifications, while the footer can be used to apply a common set of modifications to every Dockerfile.

For example, to add the networking-cisco plugin to the neutron_server image, add the following to the template-override file:

{% extends parent_template %}

{% block neutron_server_footer %}
RUN git clone \
    && pip --no-cache-dir install networking-cisco
{% endblock %}

Acute readers may notice there is one problem with this however. Assuming nothing else in the Dockerfile changes for a period of time, the above RUN statement will be cached by Docker, meaning new commits added to the Git repository may be missed on subsequent builds. To solve this the Kolla build tool also supports cloning additional repositories at build time, which will be automatically made available to the build, within an archive named plugins-archive.


The following is available for source build types only.

To use this, add a section to /etc/kolla/kolla-build.conf in the following format:


Where <image> is the image that the plugin should be installed into, and <plugin-name> is the chosen plugin identifier.

Continuing with the above example, add the following to /etc/kolla/kolla-build.conf:

type = git
location =
reference = master

The build will clone the repository, resulting in the following archive structure:

|__ plugins

The template now becomes:

{% block neutron_server_footer %}
ADD plugins-archive /
pip --no-cache-dir install /plugins/*
{% endblock %}

Custom Repos

Red Hat

The build method allows the operator to build containers from custom repos. The repos are accepted as a list of comma separated values and can be in the form of .repo, .rpm, or a url. See examples below.

Update rpm_setup_config in /etc/kolla/kolla-build.conf:

rpm_setup_config =,

If specifying a .repo file, each .repo file will need to exist in the same directory as the base Dockerfile (kolla/docker/base):

rpm_setup_config = epel.repo,delorean.repo,delorean-deps.repo


For Debian based images, additional apt sources may be added to the build as follows:

apt_sources_list = custom.list

Known issues

  1. Can’t build base image because docker fails to install systemd or httpd.

    There are some issues between docker and AUFS. The simple workaround to avoid the issue is that add -s devicemapper or -s btrfs to DOCKER_OPTS. Get more information about the issue from the Docker bug tracker and how to configure Docker with BTRFS backend.

  2. Mirrors are unreliable.

    Some of the mirrors Kolla uses can be unreliable. As a result occasionally some containers fail to build. To rectify build problems, the build tool will automatically attempt three retries of a build operation if the first one fails. The retry count is modified with the --retries option.

Docker Local Registry

It is recommended to set up local registry for Kolla developers or deploying multinode. The reason using a local registry is deployment performance will operate at local network speeds, typically gigabit networking. Beyond performance considerations, the Operator would have full control over images that are deployed. If there is no local registry, nodes pull images from Docker Hub when images are not found in local caches.

Setting up Docker Local Registry

Running Docker registry is easy. Just use the following command:

docker run -d -p 4000:5000 --restart=always --name registry \
-v <local_data_path>:/var/lib/registry registry


<local_data_path> points to the folder where Docker registry will store Docker images on the local host.

The default port of Docker registry is 5000. But the 5000 port is also the port of keystone-api. To avoid conflict, use 4000 port as Docker registry port.

Now the Docker registry service is running.

Docker Insecure Registry Config

For docker to pull images, it is necessary to modify the Docker configuration. The guide assumes that the IP of the machine running Docker registry is

In Ubuntu, add --insecure-registry to DOCKER_OPTS in /etc/default/docker.

In CentOS, uncomment INSECURE_REGISTRY and set INSECURE_REGISTRY to --insecure-registry in /etc/sysconfig/docker.

And restart the docker service.

To build and push images to local registry, use the following command:

kolla-build --registry --push

Kolla-ansible with Local Registry

To make kolla-ansible pull images from local registry, set "docker_registry" to "" in "/etc/kolla/globals.yml". Make sure Docker is allowed to pull images from insecure registry. See Docker Insecure Registry Config.

Building behind a proxy

The build script supports augmenting the Dockerfiles under build via so called header and footer files. Statements in the header file are included at the top of the base image, while those in footer are included at the bottom of every Dockerfile in the build.

A common use case for this is to insert http_proxy settings into the images to fetch packages during build, and then unset them at the end to avoid having them carry through to the environment of the final images. Note however, it’s not possible to drop the info completely using this method; it will still be visible in the layers of the image.

To use this feature, create a file called .header, with the following content for example:

ENV http_proxy=https://evil.corp.proxy:80
ENV https_proxy=https://evil.corp.proxy:80

Then create another file called .footer, with the following content:

ENV http_proxy=""
ENV https_proxy=""

Finally, pass them to the build script using the -i and -I flags:

kolla-build -i .header -I .footer

Besides this configuration options, the script will automatically read these environment variables. If the host system proxy parameters match the ones going to be used, no other input parameters will be needed. These are the variables that will be picked up from the user env:

HTTP_PROXY, http_proxy, HTTPS_PROXY, https_proxy, FTP_PROXY,
ftp_proxy, NO_PROXY, no_proxy

Also these variables could be overwritten using --build-args, which have precedence.