path: root/doc/ci/pipelines/parent_child_pipelines.md

---
stage: Verify
group: Pipeline Authoring
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
type: reference
---

# Parent-child pipelines **(FREE)**

> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/16094) in GitLab 12.7.

As pipelines grow more complex, a few related problems start to emerge:

- The staged structure, where all steps in a stage must be completed before the first
  job in next stage begins, causes arbitrary waits, slowing things down.
- Configuration for the single global pipeline becomes very long and complicated,
  making it hard to manage.
- Imports with [`include`](../yaml/index.md#include) increase the complexity of the configuration, and create the potential
  for namespace collisions where jobs are unintentionally duplicated.
- Pipeline UX can become unwieldy with so many jobs and stages to work with.

Additionally, sometimes the behavior of a pipeline needs to be more dynamic. The ability
to choose to start sub-pipelines (or not) is a powerful ability, especially if the
YAML is dynamically generated.

![Parent pipeline graph expanded](img/parent_pipeline_graph_expanded_v14_3.png)

Similarly to [multi-project pipelines](multi_project_pipelines.md), a pipeline can trigger a
set of concurrently running child pipelines, but within the same project:

- Child pipelines still execute each of their jobs according to a stage sequence, but
  would be free to continue forward through their stages without waiting for unrelated
  jobs in the parent pipeline to finish.
- The configuration is split up into smaller child pipeline configurations. Each child pipeline contains only relevant steps which are
  easier to understand. This reduces the cognitive load to understand the overall configuration.
- Imports are done at the child pipeline level, reducing the likelihood of collisions.

Child pipelines work well with other GitLab CI/CD features:

- Use [`rules: changes`](../yaml/index.md#ruleschanges) to trigger pipelines only when
  certain files change. This is useful for monorepos, for example.
- Since the parent pipeline in `.gitlab-ci.yml` and the child pipeline run as normal
  pipelines, they can have their own behaviors and sequencing in relation to triggers.

See the [`trigger`](../yaml/index.md#trigger) keyword documentation for full details on how to
include the child pipeline configuration.

<i class="fa fa-youtube-play youtube" aria-hidden="true"></i>
For an overview, see [Parent-Child Pipelines feature demo](https://youtu.be/n8KpBSqZNbk).

NOTE:
The artifact containing the generated YAML file must not be larger than 5MB.

## Examples

The simplest case is [triggering a child pipeline](../yaml/index.md#trigger) using a
local YAML file to define the pipeline configuration. In this case, the parent pipeline
triggers the child pipeline, and continues without waiting:

```yaml
microservice_a:
  trigger:
    include: path/to/microservice_a.yml
```

You can include multiple files when defining a child pipeline. The child pipeline's
configuration is composed of all configuration files merged together:

```yaml
microservice_a:
  trigger:
    include:
      - local: path/to/microservice_a.yml
      - template: Security/SAST.gitlab-ci.yml
```

In [GitLab 13.5 and later](https://gitlab.com/gitlab-org/gitlab/-/issues/205157),
you can use [`include:file`](../yaml/index.md#includefile) to trigger child pipelines
with a configuration file in a different project:

```yaml
microservice_a:
  trigger:
    include:
      - project: 'my-group/my-pipeline-library'
        ref: 'main'
        file: '/path/to/child-pipeline.yml'
```

The maximum number of entries that are accepted for `trigger:include` is three.

Similar to [multi-project pipelines](multi_project_pipelines.md#mirror-status-of-a-triggered-pipeline-in-the-trigger-job),
we can set the parent pipeline to depend on the status of the child pipeline upon completion:

```yaml
microservice_a:
  trigger:
    include:
      - local: path/to/microservice_a.yml
      - template: Security/SAST.gitlab-ci.yml
    strategy: depend
```

## Merge request child pipelines

To trigger a child pipeline as a [merge request pipeline](merge_request_pipelines.md) we need to:

- Set the trigger job to run on merge requests:

```yaml
# parent .gitlab-ci.yml
microservice_a:
  trigger:
    include: path/to/microservice_a.yml
  rules:
    - if: $CI_MERGE_REQUEST_ID
```

- Configure the child pipeline by either:

  - Setting all jobs in the child pipeline to evaluate in the context of a merge request:

    ```yaml
    # child path/to/microservice_a.yml
    workflow:
      rules:
        - if: $CI_MERGE_REQUEST_ID

    job1:
      script: ...

    job2:
      script: ...
    ```

  - Alternatively, setting the rule per job. For example, to create only `job1` in
    the context of merge request pipelines:

    ```yaml
    # child path/to/microservice_a.yml
    job1:
      script: ...
      rules:
        - if: $CI_MERGE_REQUEST_ID

    job2:
      script: ...
    ```

## Dynamic child pipelines

> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/35632) in GitLab 12.9.

Instead of running a child pipeline from a static YAML file, you can define a job that runs
your own script to generate a YAML file, which is then used to trigger a child pipeline.

This technique can be very powerful in generating pipelines targeting content that changed or to
build a matrix of targets and architectures.

<i class="fa fa-youtube-play youtube" aria-hidden="true"></i>
For an overview, see [Create child pipelines using dynamically generated configurations](https://youtu.be/nMdfus2JWHM).

We also have an example project using
[Dynamic Child Pipelines with Jsonnet](https://gitlab.com/gitlab-org/project-templates/jsonnet)
which shows how to use a data templating language to generate your `.gitlab-ci.yml` at runtime.
You could use a similar process for other templating languages like
[Dhall](https://dhall-lang.org/) or [ytt](https://get-ytt.io/).

The artifact path is parsed by GitLab, not the runner, so the path must match the
syntax for the OS running GitLab. If GitLab is running on Linux but using a Windows
runner for testing, the path separator for the trigger job would be `/`. Other CI/CD
configuration for jobs, like scripts, that use the Windows runner would use `\`.

In GitLab 12.9, the child pipeline could fail to be created in certain cases, causing the parent pipeline to fail.
This is [resolved](https://gitlab.com/gitlab-org/gitlab/-/issues/209070) in GitLab 12.10.

### Dynamic child pipeline example

> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/35632) in GitLab 12.9.

You can trigger a child pipeline from a [dynamically generated configuration file](../pipelines/parent_child_pipelines.md#dynamic-child-pipelines):

```yaml
generate-config:
  stage: build
  script: generate-ci-config > generated-config.yml
  artifacts:
    paths:
      - generated-config.yml

child-pipeline:
  stage: test
  trigger:
    include:
      - artifact: generated-config.yml
        job: generate-config
```

The `generated-config.yml` is extracted from the artifacts and used as the configuration
for triggering the child pipeline.

## Nested child pipelines

> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/29651) in GitLab 13.4.
> - [Feature flag removed](https://gitlab.com/gitlab-org/gitlab/-/issues/243747) in GitLab 13.5.

Parent and child pipelines were introduced with a maximum depth of one level of child
pipelines, which was later increased to two. A parent pipeline can trigger many child
pipelines, and these child pipelines can trigger their own child pipelines. It's not
possible to trigger another level of child pipelines.

<i class="fa fa-youtube-play youtube" aria-hidden="true"></i>
For an overview, see [Nested Dynamic Pipelines](https://youtu.be/C5j3ju9je2M).

## Pass CI/CD variables to a child pipeline

You can pass CI/CD variables to a downstream pipeline using the same methods as
multi-project pipelines:

- [By using the `variable` keyword](multi_project_pipelines.md#pass-cicd-variables-to-a-downstream-pipeline-by-using-the-variables-keyword).
- [By using variable inheritance](multi_project_pipelines.md#pass-cicd-variables-to-a-downstream-pipeline-by-using-variable-inheritance).

## Retry or cancel child pipelines

You can retry or cancel child pipelines:

- [In the main graph view](index.md#downstream-pipelines).
- In the child pipeline's details page.