Using Labels in Container Images

A standard set of docker-formatted labels are being defined by Red Hat to use in official Red Hat images, as well as in images that are produced by Red Hat Independent Software Vendor (ISV) partners. Information stored in these labels can be viewed from:

• The This content is not included.Red Hat Container Catalog in the Tech Details section for each image.
• Each image itself, using commands such as the docker inspect and atomic images info commands.

To see upstream efforts from Project Atomic to define labels and other identifiers, refer to the Content from github.com is not included.Standard Container/Application Identifiers page.

Adding Labels at Build Time

Labels can be added to a container image at build time by including Content from docs.docker.com is not included.LABEL instructions to a Dockerfile. For example, here are some LABEL instructions that would go into a Dockerfile to add labels to a MariaDB database container image at build time:

LABEL "architecture"= "x86_64"
LABEL "name"="rhscl/mariadb-100-rhel7"
LABEL version="10.0"
...

Viewing Labels from the Red Hat Container Catalog

To view labels for an existing container image (for example, mariadb) from the This content is not included.Red Hat Container Catalog, go to the container catalog, search for mariadb, select the appropriate image, and select Tech Details from the image page. Labels are listed at the end of the Image Metadata information. For example:

Labels 
    io.k8s.description MariaDB is a multi-user, multi-threaded SQL database server
    Version 10.1
    vcs-ref 038365d843b36f9507078d710b4e86f36807645f
    authoritative-source-url registry.access.redhat.com
    Vendor Red Hat, Inc.
    io.k8s.display-name MariaDB 10.1
    version 10.1
    com.redhat.component rh-mariadb101-docker
    distribution-scope public
    vendor Red Hat, Inc.
    Name rhscl/mariadb-101-rhel7
    Build_Host ip-10-29-120-226.ec2.internal
    vcs-type git
    Architecture x86_64
    Release 3.4
    BZComponent rh-mariadb101-docker
    build-date 2016-10-31T06:51:03.889352Z
    name rhscl/mariadb-101-rhel7
    summary MariaDB is a multi-user, multi-threaded SQL database server
    architecture x86_64
    release 3.4
    io.openshift.expose-services 3306:mysql
    io.openshift.tags database,mysql,mariadb,mariadb101,rh-mariadb101
    com.redhat.build-host ip-10-29-120-226.ec2.internal

Viewing Label Information from the Command Line

To view label information for an image that is accessible from a system running the docker service (for example, a mariadb image) using commands, type either of the following:

  # docker inspect rhscl/mariadb-100-rhel7
  ...
            "Labels": {
                  "Architecture": "x86_64",
                  "BZComponent": "rh-mariadb100-docker",
  ...
  # atomic images info rhscl/mariadb-100-rhel7  
  Image Name: registry.access.redhat.com/rhscl/mariadb-100-rhel7:latest
  io.k8s.description: MariaDB is a multi-user, multi-threaded SQL database server
  Version: 10.0
  vcs-ref: e6efd72fcf0daf102255ae44c59c1e408df8171b
  authoritative-source-url: registry.access.redhat.com
  Vendor: Red Hat, Inc.
  io.k8s.display-name: MariaDB 10.0
  ...

Label Definitions

The following table describes container labels used in Red Hat container images. Some of these labels are added with LABEL instructions while others are created automatically at build time:

NOTE: Uppercase versions of some of the labels just shown were supported in earlier container images. Examples of these are Name, Release, Vendor, and others. Red Hat expects to remove those label names for RHEL 7.3.2. Therefore, you should not write scripts or put processes in place to automatically read those older-style labels.

There are some labels that are used specifically to provide information to the atomic command that tell it what docker or other command to run with different options to atomic. For example, the RUN label defines the full docker command and options to run when you run an atomic run command on a container. Here is a list of those labels: