Document How to manage runner jobs during upgrades

doc/update/index.md

@@ -138,6 +138,19 @@ pending_job_classes = scheduled_queue.select { |job| job["class"] == "Background
 pending_job_classes.each { |job_class| Gitlab::BackgroundMigration.steal(job_class) }
 ```
 
+## Dealing with running CI/CD pipelines and jobs
+
+If you upgrade your GitLab instance while the GitLab Runner is processing jobs, the trace updates will fail. Once GitLab is back online, then the trace updates should self-heal. However, depending on the error, the GitLab Runner will either retry or eventually terminate job handling.
+
+As for the artifacts, the GitLab Runner will attempt to upload them three times, after which the job will eventually fail.
+
+To address the above two scenario's, it is adviced to do the following prior to upgrading:
+
+1. Plan your maintenance.
+1. Pause your runners.
+1. Wait until all jobs are finished.
+1. Upgrade GitLab.
+
 ## Checking for pending Advanced Search migrations
 
 This section is only applicable if you have enabled the [Elasticsearch