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Summary

Instanced pipelines group together pipelines which share a common template configured with different ((vars)). They provide a simple two-level hierarchy and automatic archiving of instances which are no longer needed.

Proposal

Pipelines can be configured with 'instance vars' like so:

fly set-pipeline -p branch --instance-var branch=feature/foo

These may also be specified on the set_pipeline step like so:

set_pipeline: branch
instance_vars: {branch: feature/foo}

Both of the above examples will configure a branch pipeline, with the ((branch)) var set to "feature/foo".

Instance vars are used as part of the pipeline identifier in the UI and API. There can be multiple instances of a pipeline with the same name:

fly set-pipeline -p branch --instance-var branch=feature/foo
fly set-pipeline -p branch --instance-var branch=feature/bar

Instanced pipelines sharing the same name will be grouped together in the web UI.

An individual instance of a pipeline can be manually destroyed, paused, and archived (RFC #33):

fly destroy-pipeline -p branch -i branch:feature/foo
fly pause-pipeline   -p branch -i branch:feature/foo
fly archive-pipeline -p branch -i branch:feature/foo

(Side note: : vs. = is a little weird but it's consistent with fly check-resource - we use = for assignment and : for partial filtering.)

Automatic archival

Instanced pipelines build on the automatic pipeline archiving introduced in RFC #33. Individual pipeline instances that are no longer configured will be automatically archived in the same way that normal pipelines would.

For example, say I have a job whose build plan configures a pipeline instance for each supported version:

plan:
- get: ci
- set_pipeline: release
  file: ci/pipelines/release.yml
  instance_vars:
    version: 5.3
- set_pipeline: release
  file: ci/pipelines/release.yml
  instance_vars:
    version: 5.2

Let's say I ship a 5.5 version, and my policy is to only support the last 2 versions. I would update the config like so:

plan:
- get: ci
- set_pipeline: release
  file: ci/pipelines/release.yml
  instance_vars:
    version: 5.4
- set_pipeline: release
  file: ci/pipelines/release.yml
  instance_vars:
    version: 5.3

When this build runs, the version: 5.2 instance will be automatically archived.

New Implications

This functionality will be more and more useful as we expand Concourse's vocabulary to support pipeline automation. Spatial resources (RFC #29), for example, can be used to automatically configure a pipeline for each branch or PR. When the branch or PR goes away, their pipeline instances will be archived automatically.