147 lines
5.3 KiB
Markdown
147 lines
5.3 KiB
Markdown
---
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type: reference
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---
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# Parent-child pipelines
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> [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/16094) in GitLab 12.7.
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As pipelines grow more complex, a few related problems start to emerge:
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- The staged structure, where all steps in a stage must be completed before the first
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job in next stage begins, causes arbitrary waits, slowing things down.
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- Configuration for the single global pipeline becomes very long and complicated,
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making it hard to manage.
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- Imports with [`include`](yaml/README.md#include) increase the complexity of the configuration, and create the potential
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for namespace collisions where jobs are unintentionally duplicated.
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- Pipeline UX can become unwieldy with so many jobs and stages to work with.
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Additionally, sometimes the behavior of a pipeline needs to be more dynamic. The ability
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to choose to start sub-pipelines (or not) is a powerful ability, especially if the
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YAML is dynamically generated.
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Similarly to [multi-project pipelines](multi_project_pipelines.md), a pipeline can trigger a
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set of concurrently running child pipelines, but within the same project:
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- Child pipelines still execute each of their jobs according to a stage sequence, but
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would be free to continue forward through their stages without waiting for unrelated
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jobs in the parent pipeline to finish.
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- The configuration is split up into smaller child pipeline configurations, which are
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easier to understand. This reduces the cognitive load to understand the overall configuration.
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- Imports are done at the child pipeline level, reducing the likelihood of collisions.
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- Each pipeline has only relevant steps, making it easier to understand what's going on.
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Child pipelines work well with other GitLab CI features:
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- Use [`only: changes`](yaml/README.md#onlychangesexceptchanges) to trigger pipelines only when
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certain files change. This is useful for monorepos, for example.
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- Since the parent pipeline in `.gitlab-ci.yml` and the child pipeline run as normal
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pipelines, they can have their own behaviors and sequencing in relation to triggers.
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All of this will work with the [`include:`](yaml/README.md#include) feature so you can compose
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the child pipeline configuration.
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## Examples
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The simplest case is [triggering a child pipeline](yaml/README.md#trigger) using a
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local YAML file to define the pipeline configuration. In this case, the parent pipeline will
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trigger the child pipeline, and continue without waiting:
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```yaml
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microservice_a:
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trigger:
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include: path/to/microservice_a.yml
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```
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You can include multiple files when composing a child pipeline:
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```yaml
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microservice_a:
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trigger:
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include:
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- local: path/to/microservice_a.yml
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- template: SAST.gitlab-ci.yml
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```
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NOTE: **Note:**
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The max number of entries that are accepted for `trigger:include:` is three.
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Similar to [multi-project pipelines](multi_project_pipelines.md#mirroring-status-from-triggered-pipeline),
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we can set the parent pipeline to depend on the status of the child pipeline upon completion:
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```yaml
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microservice_a:
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trigger:
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include:
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- local: path/to/microservice_a.yml
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- template: SAST.gitlab-ci.yml
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strategy: depend
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```
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## Merge Request child pipelines
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To trigger a child pipeline as a [Merge Request Pipeline](merge_request_pipelines/index.md) we need to:
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- Set the trigger job to run on merge requests:
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```yaml
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# parent .gitlab-ci.yml
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microservice_a:
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trigger:
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include: path/to/microservice_a.yml
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rules:
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- if: $CI_MERGE_REQUEST_ID
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```
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- Configure the child pipeline by either:
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- Setting all jobs in the child pipeline to evaluate in the context of a merge request:
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```yaml
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# child path/to/microservice_a.yml
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workflow:
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rules:
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- if: $CI_MERGE_REQUEST_ID
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job1:
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script: ...
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job2:
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script: ...
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```
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- Alternatively, setting the rule per job. For example, to create only `job1` in
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the context of merge request pipelines:
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```yaml
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# child path/to/microservice_a.yml
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job1:
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script: ...
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rules:
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- if: $CI_MERGE_REQUEST_ID
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job2:
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script: ...
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```
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## Dynamic child pipelines
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> [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/35632) in GitLab 12.9.
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Instead of running a child pipeline from a static YAML file, you can define a job that runs
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your own script to generate a YAML file, which is then [used to trigger a child pipeline](yaml/README.md#trigger-child-pipeline-with-generated-configuration-file).
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This technique can be very powerful in generating pipelines targeting content that changed or to
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build a matrix of targets and architectures.
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## Limitations
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A parent pipeline can trigger many child pipelines, but a child pipeline cannot trigger
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further child pipelines. See the [related issue](https://gitlab.com/gitlab-org/gitlab/issues/29651)
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for discussion on possible future improvements.
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When triggering dynamic child pipelines, if the job containing the CI config artifact is not a predecessor of the
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trigger job, the child pipeline will fail to be created, causing also the parent pipeline to fail.
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In the future we want to validate the trigger job's dependencies [at the time the parent pipeline is created](https://gitlab.com/gitlab-org/gitlab/-/issues/209070) rather than when the child pipeline is created.
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