How to get merge request ID on Gitlab master pipeline?

I love automating daily processes and I recently noticed a problem with my team’s deployment processes on monorepo. Collecting and announcing MRs to stakeholders during deployment was tedious and prone to human error. Therefore, I developed a pipeline integration that automates deployment announcements. The flow was as follows:

• When release MR is created, a deployment announcement is sent from the pipeline to the Slack channel.
• When release MR is merged, it is announced under the announcement message that the deployment has started.
• When the release pipeline is finished, a message containing the metrics related to the deployment process is sent and the completion of the deployment is announced.

To calculate some metrics, we need to know the creation time of the merge request. This means we technically need the merge request ID in the master pipeline.

On the merge request pipeline

You can use the CI_MERGE_REQUEST_IID predefined variable to get the merge request id in the merge request pipeline. If you set the variable value to undefined, you need to add a rule that commits the job to run in the merge request pipeline.

.enable-on-merge-request-pipeline:
  rules:
    - if: $CI_PIPELINE_SOURCE == "merge_request_event"

On the master pipeline

Since there is no merge request in the master pipeline anymore, things are different. After obtaining the commit SHA value with CI_COMMIT_SHA predefined variable, it is necessary to make a request to GitLab API as follows.

curl \
--location 'https://gitlab.{{companyName}}.com/api/v4/projects/{{projectId}}/repository/commits/{{commitSha}}/merge_requests' \
--header 'PRIVATE-TOKEN: {{token}}

Matching merge requests will be returned as response. In case more than one merge request is returned, you can compare it with the CI_COMMIT_TITLE predefined variable.

After a challenging path, we reach our goal. While you solve your problem, I might as well complete my automation journey ☕