10.4. Creating objects from templates by using the CLI

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.

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=-