10.4. Creating objects from templates by using the CLI

You can use the CLI to process templates and use the configuration that is generated to create objects.

10.4.1. Adding labels

Labels are used to manage and organize generated objects, such as pods. The labels specified in the template are applied to every object that is generated from the template.

Procedure

  • Add labels in the template from the command line:

    $ oc process -f <filename> -l name=otherLabel

10.4.2. Listing parameters

The list of parameters that you can override are listed in the parameters section of the template.

Procedure

  1. You can list parameters with the CLI by using the following command and specifying the file to be used:

    $ oc process --parameters -f <filename>

    Alternatively, if the template is already uploaded:

    $ oc process --parameters -n <project> <template_name>

    For example, the following shows the output when listing the parameters for one of the Quickstart templates in the default openshift project:

    $ oc process --parameters -n openshift rails-postgresql-example

    Example output

    NAME                         DESCRIPTION                                                                                              GENERATOR           VALUE
    SOURCE_REPOSITORY_URL        The URL of the repository with your application source code                                                                  https://github.com/sclorg/rails-ex.git
    SOURCE_REPOSITORY_REF        Set this to a branch name, tag or other ref of your repository if you are not using the default branch
    CONTEXT_DIR                  Set this to the relative path to your project if it is not in the root of your repository
    APPLICATION_DOMAIN           The exposed hostname that will route to the Rails service                                                                    rails-postgresql-example.openshiftapps.com
    GITHUB_WEBHOOK_SECRET        A secret string used to configure the GitHub webhook                                                     expression          [a-zA-Z0-9]{40}
    SECRET_KEY_BASE              Your secret key for verifying the integrity of signed cookies                                            expression          [a-z0-9]{127}
    APPLICATION_USER             The application user that is used within the sample application to authorize access on pages                                 openshift
    APPLICATION_PASSWORD         The application password that is used within the sample application to authorize access on pages                             secret
    DATABASE_SERVICE_NAME        Database service name                                                                                                        postgresql
    POSTGRESQL_USER              database username                                                                                        expression          user[A-Z0-9]{3}
    POSTGRESQL_PASSWORD          database password                                                                                        expression          [a-zA-Z0-9]{8}
    POSTGRESQL_DATABASE          database name                                                                                                                root
    POSTGRESQL_MAX_CONNECTIONS   database max connections                                                                                                     10
    POSTGRESQL_SHARED_BUFFERS    database shared buffers                                                                                                      12MB

    The output identifies several parameters that are generated with a regular expression-like generator when the template is processed.

10.4.3. Generating a list of objects

Using the CLI, you can process a file defining a template to return the list of objects to standard output.

Procedure

  1. Process a file defining a template to return the list of objects to standard output:

    $ oc process -f <filename>

    Alternatively, if the template has already been uploaded to the current project:

    $ oc process <template_name>
  2. Create objects from a template by processing the template and piping the output to oc create:

    $ oc process -f <filename> | oc create -f -

    Alternatively, if the template has already been uploaded to the current project:

    $ oc process <template> | oc create -f -
  3. You can override any parameter values defined in the file by adding the -p option for each <name>=<value> pair you want to override. A parameter reference appears in any text field inside the template items.

    For example, in the following the POSTGRESQL_USER and POSTGRESQL_DATABASE parameters of a template are overridden to output a configuration with customized environment variables:

    1. Creating a List of objects from a template

      $ oc process -f my-rails-postgresql \
          -p POSTGRESQL_USER=bob \
          -p POSTGRESQL_DATABASE=mydatabase
    2. The JSON file can either be redirected to a file or applied directly without uploading the template by piping the processed output to the oc create command:

      $ oc process -f my-rails-postgresql \
          -p POSTGRESQL_USER=bob \
          -p POSTGRESQL_DATABASE=mydatabase \
          | oc create -f -
    3. If you have large number of parameters, you can store them in a file and then pass this file to oc process:

      $ cat postgres.env
      POSTGRESQL_USER=bob
      POSTGRESQL_DATABASE=mydatabase
      $ oc process -f my-rails-postgresql --param-file=postgres.env
    4. You can also read the environment from standard input by using "-" as the argument to --param-file:

      $ sed s/bob/alice/ postgres.env | oc process -f my-rails-postgresql --param-file=-