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---
type: reference
---
# Parent-child pipelines
> [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/README.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.
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, 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.
- Each pipeline has only relevant steps, making it easier to understand what's going on.
Child pipelines work well with other GitLab CI/CD features:
- Use [`only: changes`](yaml/README.md#onlychangesexceptchanges) 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.
All of this will work with the [`include:`](yaml/README.md#include) feature so you can compose
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).
## Examples
The simplest case is [triggering a child pipeline](yaml/README.md#trigger) using a
local YAML file to define the pipeline configuration. In this case, the parent pipeline will
trigger the child pipeline, and continue without waiting:
```yaml
microservice_a:
trigger:
include: path/to/microservice_a.yml
```
You can include multiple files when composing a child pipeline:
```yaml
microservice_a:
trigger:
include:
- local: path/to/microservice_a.yml
- template: SAST.gitlab-ci.yml
```
NOTE: **Note:**
The max number of entries that are accepted for `trigger:include:` is three.
Similar to [multi-project pipelines](multi_project_pipelines.md#mirroring-status-from-triggered-pipeline),
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: SAST.gitlab-ci.yml
strategy: depend
```
## Merge Request child pipelines
To trigger a child pipeline as a [Merge Request Pipeline](merge_request_pipelines/index.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](yaml/README.md#trigger-child-pipeline-with-generated-configuration-file).
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).
In GitLab 12.9, the child pipeline could fail to be created in certain cases, causing the parent pipeline to fail.
This is [resolved in GitLab 12.10](https://gitlab.com/gitlab-org/gitlab/-/issues/209070).
## Limitations
A parent pipeline can trigger many child pipelines, but a child pipeline cannot trigger
further child pipelines. See the [related issue](https://gitlab.com/gitlab-org/gitlab/issues/29651)
for discussion on possible future improvements.
|
