We have seen that build runners can be very handy. Even though most build runners can be replaced with an equivalent command using the command-line runner, build runners come with the convenience of easily setting up build steps, along with the necessary agent requirements and parameters.

Meta-Runners provide a straightforward way to create custom build runners. Meta-Runners can be thought of as a way to avoid duplications in build steps across build configurations.

In Chapter 3, Getting Your CI Up and Running, we created the deploy-to-test build configuration that deploys the Django application to Heroku. Using this build configuration as an example, we can see how we can extract a Meta-Runner Deploy To Heroku that can be used by any build configuration that wants to deploy to Heroku.

Recall that the deploy-to-test build configuration had a simple command-line runner that executed the following commands:

git remote add heroku git@heroku.com:django-ci-example.git  git push heroku master

To create a generic Meta-Runner out of this, we need to provide a way to push to any remote, rather than just git@heroku.com:django-ci-example.git.

As expected, we will do this by extracting the remote out into a build parameter. The command-line runner will have the following as the Custom Script to be run:

git remote add heroku %heroku.remote%  git push heroku master

We will provide the value for the %heroku.remote% parameter in the Build Parameters section of the build configuration.

Now we are ready to create a Meta-Runner from this build configuration. This can be done by clicking on the Extract Meta-Runner button in the right-hand side bar of the build configuration settings page. This brings up the Extract Meta-Runner dialog, which is shown in the following screenshot:

In the dialog, we give a name to the Meta-Runner. This is the name that will appear in the Runner Type field when configuring a build step for a build configuration.

Click on Extract to create the Meta-Runner. Once the Meta-Runner is created, we can see it listed in the Meta-Runners tab on the project administration page. We can also edit the Meta-Runner to fine-tune it as desired.

The following screenshot shows the edit page of the Deploy To Heroku Meta-Runner that we just created:

The Meta-Runner extracts all the parameters and steps defined in the build configuration. We can edit the Meta-Runner to have only the necessary parameters and steps.

Using Meta-Runners

We can now use the Meta-Runner that we created pretty much like a normal build runner. We will remove the existing build step in the deploy-to-test build configuration (from which we extracted the Meta-Runner) and add a Deploy To Heroku Meta-Runner-based build step.

Tip

We can also disable build steps if we don’t want to remove them while experimenting.

In the New Build Step page, for the Runner type field, the newly created Deploy To Heroku Meta-Runner is available, as shown in the following screenshot:

Once we choose the Deploy To Heroku Meta-Runner, we can see that the heroku.remote parameter is one of the fields to be configured. Since we created the Meta-Runner with the heroku.remote parameter with the value git@heroku.com:django-ci-example.git, that remote is available by default. The Deploy To Heroku runner configuration page is shown in the following screenshot:

Tip

It is possible to remove the value for parameters in the Meta-Runner XML so that no default values are present for the fields.

We can click on Save to add the build step. The new build step, based on the Deploy To Heroku Meta-Runner, will function in the same way as the previous build step based on the command-line runner.

Note

Of course, the value of Meta-Runners becomes more apparent when we create them out of multiple build steps. The same set of steps that may be repeated across multiple configurations can be extracted i

Rajesh Kumar

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