213 lines
7.4 KiB
Markdown
213 lines
7.4 KiB
Markdown
---
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type: reference, index
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last_update: 2019-07-03
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---
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# Pipelines for Merge Requests
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> [Introduced](https://gitlab.com/gitlab-org/gitlab-foss/issues/15310) in GitLab 11.6.
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Usually, when you create a new merge request, a pipeline runs with the
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new change and checks if it's qualified to be merged into a target branch. This
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pipeline should contain only necessary jobs for validating the new changes.
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For example, unit tests, lint checks, and [Review Apps](../review_apps/index.md)
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are often used in this cycle.
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With pipelines for merge requests, you can design a specific pipeline structure
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for when you are running a pipeline in a merge request. This
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could be either adding or removing steps in the pipeline, to make sure that
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your pipelines are as efficient as possible.
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## Requirements and limitations
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Pipelines for merge requests have the following requirements and limitations:
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- As of GitLab 11.10, pipelines for merge requests require GitLab Runner 11.9
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or higher due to the
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[recent refspecs changes](https://gitlab.com/gitlab-org/gitlab-foss/merge_requests/25504).
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- Pipelines for merge requests are incompatible with
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[CI/CD for external repositories](../ci_cd_for_external_repos/index.md).
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## Configuring pipelines for merge requests
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To configure pipelines for merge requests, add the `only: [merge_requests]` parameter to
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the jobs that you want to run only for merge requests.
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Then, when developers create or update merge requests, a pipeline runs
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every time a commit is pushed to GitLab.
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NOTE: **Note**:
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If you use this feature with [merge when pipeline succeeds](../../user/project/merge_requests/merge_when_pipeline_succeeds.md),
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pipelines for merge requests take precedence over the other regular pipelines.
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For example, consider the following [`.gitlab-ci.yml`](../yaml/README.md):
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```yaml
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build:
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stage: build
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script: ./build
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only:
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- master
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test:
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stage: test
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script: ./test
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only:
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- merge_requests
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deploy:
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stage: deploy
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script: ./deploy
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only:
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- master
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```
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After the merge request is updated with new commits:
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- GitLab detects that changes have occurred and creates a new pipeline for the merge request.
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- The pipeline fetches the latest code from the source branch and run tests against it.
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In the above example, the pipeline contains only a `test` job.
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Since the `build` and `deploy` jobs don't have the `only: [merge_requests]` parameter,
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they will not run in the merge request.
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Pipelines tagged with the **detached** badge indicate that they were triggered
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when a merge request was created or updated. For example:
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![Merge request page](img/merge_request.png)
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## Pipelines for Merged Results **(PREMIUM)**
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Read the [documentation on Pipelines for Merged Results](pipelines_for_merged_results/index.md).
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### Merge Trains **(PREMIUM)**
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Read the [documentation on Merge Trains](pipelines_for_merged_results/merge_trains/index.md).
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## Excluding certain jobs
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The behavior of the `only: [merge_requests]` parameter is such that _only_ jobs with
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that parameter are run in the context of a merge request; no other jobs will be run.
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However, you may want to reverse this behavior, having all of your jobs to run _except_
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for one or two.
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Consider the following pipeline, with jobs `A`, `B`, and `C`. Imagine you want:
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- All pipelines to always run `A` and `B`.
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- `C` to run only for merge requests.
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To achieve this, you can configure your `.gitlab-ci.yml` file as follows:
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``` yaml
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.only-default: &only-default
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only:
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- master
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- merge_requests
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- tags
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A:
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<<: *only-default
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script:
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- ...
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B:
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<<: *only-default
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script:
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- ...
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C:
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script:
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- ...
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only:
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- merge_requests
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```
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Therefore:
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- Since `A` and `B` are getting the `only:` rule to execute in all cases, they will always run.
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- Since `C` specifies that it should only run for merge requests, it will not run for any pipeline
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except a merge request pipeline.
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As you can see, this will help you avoid a lot of boilerplate where you'd need
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to add that `only:` rule to all of your jobs in order to make them always run. You
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can use this for scenarios like having only pipelines with merge requests get a
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Review App set up, helping to save resources.
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## Excluding certain branches
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Pipelines for merge requests require special treatement when
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using [`only`/`except`](../yaml/README.md#onlyexcept-basic). Unlike ordinary
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branch refs (for example `refs/heads/my-feature-branch`), merge request refs
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use a special Git reference that looks like `refs/merge-requests/:iid/head`. Because
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of this, the following configuration will **not** work as expected:
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```yaml
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# Does not exclude a branch named "docs-my-fix"!
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test:
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only: [merge_requests]
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except: [/^docs-/]
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```
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Instead, you can use the
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[`$CI_COMMIT_REF_NAME` predefined environment
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variable](../variables/predefined_variables.md#variables-reference) in
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combination with
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[`only:variables`](../yaml/README.md#onlyvariablesexceptvariables) to
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accomplish this behavior:
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```yaml
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test:
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only: [merge_requests]
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except:
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variables:
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$CI_COMMIT_REF_NAME =~ /^docs-/
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```
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## Important notes about merge requests from forked projects
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Note that the current behavior is subject to change. In the usual contribution
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flow, external contributors follow the following steps:
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1. Fork a parent project.
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1. Create a merge request from the forked project that targets the `master` branch
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in the parent project.
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1. A pipeline runs on the merge request.
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1. A maintainer from the parent project checks the pipeline result, and merge
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into a target branch if the latest pipeline has passed.
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Currently, those pipelines are created in a **forked** project, not in the
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parent project. This means you cannot completely trust the pipeline result,
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because, technically, external contributors can disguise their pipeline results
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by tweaking their GitLab Runner in the forked project.
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There are multiple reasons why GitLab doesn't allow those pipelines to be
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created in the parent project, but one of the biggest reasons is security concern.
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External users could steal secret variables from the parent project by modifying
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`.gitlab-ci.yml`, which could be some sort of credentials. This should not happen.
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We're discussing a secure solution of running pipelines for merge requests
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that are submitted from forked projects,
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see [the issue about the permission extension](https://gitlab.com/gitlab-org/gitlab-foss/issues/23902).
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## Additional predefined variables
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By using pipelines for merge requests, GitLab exposes additional predefined variables to the pipeline jobs.
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Those variables contain information of the associated merge request, so that it's useful
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to integrate your job with [GitLab Merge Request API](../../api/merge_requests.md).
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You can find the list of available variables in [the reference sheet](../variables/predefined_variables.md).
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The variable names begin with the `CI_MERGE_REQUEST_` prefix.
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<!-- ## Troubleshooting
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