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Applies to SUSE Linux Enterprise Server 12 SP3

5 Creating Custom Images Edit source

For creating your custom image you need a base Docker image of SLES. You can use any of the pre-built SLES images that you can obtain as described in Section 5.2, “Customizing SLES Docker Images”.

Note
Note: No SLES Images in Docker Hub

Usually you can pull a variety of base Docker images from the docker hub but that does not apply for SLES. Currently we cannot distribute SLES images for Docker Open Source Engine because there is no way to associate an End-User License Agreement (EULA) to a Docker image. sle2docker enables you to import pre-built SLES images that you can use for creating base SLES images.

After you obtain your base docker image, you can modify the image by using a Dockerfile (usually placed in the build directory). Then use the standard building tool to create your custom image:

         docker build path_to_build_directory

For more docker build options please refer to the official Docker documentation.

Note
Note: Dockerizing Your Applications

You may want to write a dockerfile for your own application that should be run inside a docker container. For a procedure refer to Chapter 6, Creating Docker Images of Applications.

5.1 Obtaining Base SLES Images Edit source

You can install pre-built images of SLES by using Zypper:

        sudo zypper in sles11sp4-docker-image suse-sles12sp3-image

Pre-built images do not have repositories configured. But when the Docker host has an SLE subscription that provides access to the product used in the image, Zypper will automatically have access to the right repositories.

After the pre-built images are installed, you need to list them using sle2docker to get a proper image name:

        sle2docker list

Now you need to activate the pre-built images:

        sle2docker activate PRE-BUILT_IMAGE_NAME

After successful activation, sle2docker will display the name of the Docker image. You can customize the docker image as described in Section 5.2, “Customizing SLES Docker Images”.

5.2 Customizing SLES Docker Images Edit source

The pre-built images do not have any repository configured and do not include any modules or extensions. They contain a zypper service that contacts either the SUSE Customer Center (SCC) or your Subscription Management Tool (SMT) server, according to the configuration of the SLE host that runs the Docker container. The service obtains the list of repositories available for the product used by the Docker image. You can also directly declare extensions in your Dockerfile (for details refer to Section 5.2.3, “Adding SLE Extensions and Modules to Images”.

You do not need to add any credentials to the Docker image because the machine credentials are automatically injected into the container by the Docker daemon. They are injected inside of the /run/secrets directory. The same applies to the /etc/SUSEConnect file of the host system, which is automatically injected into the /run/secrets directory.

Note
Note: Credentials and Security

The contents of the /run/secrets directory are never committed to a Docker image, hence there is no risk of your credentials leaking.

Note
Note: Building Images on Systems Registered with RMT

When the host system used for building Docker images is registered against RMT, the default behavior allows only building containers of the same code base as the host. For example, if your Docker host is a SLE 15 system you can only build SLE 15-based images on that host by default. To build images for a different SLE version, for example SLE 12 on a SLE 15 host, the host machine credentials for the target release can be injected into the container as outlined below.

When the host system is registered again SUSE Customer Center this restriction does not apply.

Note
Note: Building Container Images in On-Demand SLE Instances in the Public Cloud

When building container images on SLE instances that were launched as so-called "on-demand" or "pay as you go" instances on a Public Cloud (AWS, GCE, or Azure), some additional steps have to be performed. For installing packages and updates, the "on-demand" public cloud instances are connected to a public cloud-specific update infrastructure, which is based on RMT servers operated by SUSE on the various Public Cloud Providers. Some additional steps are required to locate the required services and authenticate with them.

A new service was introduced to enable this, called containerbuild-regionsrv. This service is available in the public cloud images provided through the Marketplaces of the various Public Cloud Providers. So before building an image, this service has to be started on the public cloud instance by running the following command:

tux > sudo systemctl start containerbuild-regionsrv

To start it automatically after system startup, enable it with systemctl:

tux > sudo systemctl enable containerbuild-regionsrv

The Zypper plugins provided by the SLE base images will then connect to this service for retrieving authentication details and information about which update server to talk to. In order for that to work the container has to be built with host networking enabled, like the following example:

tux > docker build --network host build-directory/

Since update infrastructure in the Public Clouds is based upon RMT, the same restrictions with regard to building SLE images for SLE versions differing from the SLE version of the host apply here as well (see Note: Building Images on Systems Registered with RMT).

To obtain the list of repositories use the following command:

zypper ref -s

It will automatically add all the repositories to your container. For each repository added to the system a new file will be created under /etc/zypp/repos.d. The URLs of these repositories include an access token that automatically expires after 12 hours. To renew the token call the zypper ref -s command. It is secure to commit these files to a Docker image.

If you want to use a different set of credentials, place a custom /etc/zypp/credentials.d/SCCcredentials file inside of the Docker image. It contains the machine credentials that have the subscription you want to use. The same applies to the SUSEConnect file: to override the file available on the host system that is running the Docker container, add a custom /etc/SUSEConnect file inside of the Docker image.

Now you can create a custom Docker image by using a Dockerfile. If you want to create a custom SLE 12 image, please refer to Section 5.2.1, “Creating a Custom SLE 12 Image”. If you want to create a custom SLE 11 SP3 Docker image, please refer to Section 5.2.2, “Creating a Custom SLE 11 SP4 Image”. In case you would like to move your application to a Docker container, please refer to Chapter 6, Creating Docker Images of Applications.

5.2.1 Creating a Custom SLE 12 Image Edit source

The following Dockerfile creates a simple Docker image based on SLE 12 SP3:

FROM suse/sles12sp3:latest

RUN zypper ref -s
RUN zypper -n in vim

When the Docker host machine is registered against an internal SMT server, the Docker image requires the SSL certificate used by SMT:

FROM suse/sles12sp3:latest

# Import the crt file of our private SMT server
ADD http://smt.test.lan/smt.crt /etc/pki/trust/anchors/smt.crt
RUN update-ca-certificates

RUN zypper ref -s
RUN zypper -n in vim

5.2.2 Creating a Custom SLE 11 SP4 Image Edit source

The following Dockerfile creates a simple Docker image based on SLE 11 SP4:

FROM suse/sles11sp4:latest

RUN zypper ref -s
RUN zypper -n in vim

When the Docker host machine is registered against an internal SMT server, the Docker image requires the SSL certificate used by SMT:

FROM suse/sles11sp4:latest

# Import the crt file of our private SMT server
ADD http://smt.test.lan/smt.crt /etc/ssl/certs/smt.pem
RUN c_rehash /etc/ssl/certs

RUN zypper ref -s
RUN zypper -n in vim

5.2.3 Adding SLE Extensions and Modules to Images Edit source

You may have subscriptions to SLE extensions or modules that you would like to use in your custom image. To add them to the Docker image, proceed as follows:

Procedure 5.1: Adding Extension and Modules
  1. Add the following into your Dockerfile:

    ADD *.repo /etc/zypp/repos.d/
    ADD *.service /etc/zypp/services.d
    RUN zypper refs && zypper refresh
  2. Copy all .service and .repo files that you will use into the directory where you will build the Docker image from the Dockerfile.

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