Configuration Management Strategies
When building pipelines, there are many possible strategies for structuring your configuration in source control as well as in pipeline design. No single method can cover all situations. After reading this document, we hope you feel equipped to select an approach.
Single Repository for Each Foundation
This is the simplest thing that could possibly work. It's the default assumed in all our examples, unless we've articulated a specific reason to choose a different approach. It entails using a single Git repository for each foundation.
Tracking foundation changes are simple, getting started is easy, duplicating foundations is simply a matter of cloning a repository, and configuration files are not difficult to understand.
Let's examine an example configuration repository that uses the "Single Repository for each Foundation" pattern:
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Notice that there is only one subdirectory
and that all other files are at the repositories base directory.
This minimizes parameter mapping in the platform-automation tasks.
For example, in the
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We map the config files
to the expected input named
env of the
configure-director task's default
ENV parameter is
it automatically uses the
env.yml file in our configuration repo.
We do not need to explicitly name the
ENV parameter for the task.
This also works for
Another option for mapping resources to inputs is discussed in the Matching Resource Names and Input Names section.
For reference, here is the
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Multiple Foundations with one Repository
Multiple foundations may use a single Git configuration source but have different variables loaded from a foundation specific vars file, Credhub, Git repository, etc. This approach is very similar to the Single Repository for Each Foundation described above, except that variables are loaded in from external sources.
The variable source may be loaded in a number of ways. For example, it may be loaded from a separate foundation specific Git repository, a foundation specific subdirectory in the configuration source, or even a foundation specific vars file found in the base Git configuration.
This strategy can reduce the number of overall configuration files and configuration repositories in play, and can reduce foundation drift (as the basic configuration is being pulled from a single source). However, configuration management and secrets handling can quickly become more challenging.
This is the strategy used in our Reference Pipeline
Advanced Pipeline Design
Matching Resource Names and Input Names
Alternatively, we can create resources that match the input names
on our tasks and bypass the need for using
Even if these resources map to the same git repository and branch,
they can be declared as separate inputs.
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As long as those resources have an associated
in the job, they will automatically be mapped to the inputs of the tasks in that job:
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If you have two resources defined with the same git repository, such as env and config, and have a passed constraint on only one of them, there is a possibility that they will not be at the same SHA for any given job in your pipeline.
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Modifying Resources in-place
Concourse 5+ Only
This section uses a Concourse feature that allows inputs and outputs to have the same name. This feature is only available in Concourse 5+. The following does not work with Concourse 4.
In certain circumstances, resources can be modified by one task in a job for use later in that same job. A few tasks that offer this ability include:
For each of these tasks,
output_mapping can be used to "overwrite"
an input with a modified input for use with tasks later in that job.
In the following example,
prepare-tasks-with-secrets takes in the
platform-automation-tasks input and modifies it for the
task. A more in-depth explanation of this can be found on the secrets-handling page.
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