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+# Automatic CE->EE merge
+
+GitLab Community Edition is merged automatically every 3 hours into the
+Enterprise Edition (look for the [`CE Upstream` merge requests]).
+
+This merge is done automatically in a
+[scheduled pipeline](https://gitlab.com/gitlab-org/release-tools/-/jobs/43201679).
+If a merge is already in progress, the job [doesn't create a new one](https://gitlab.com/gitlab-org/release-tools/-/jobs/43157687).
+
+**If you are pinged in a `CE Upstream` merge request to resolve a conflict,
+please resolve the conflict as soon as possible or ask someone else to do it!**
+
+>**Note:**
+It's ok to resolve more conflicts than the one that you are asked to resolve. In
+that case, it's a good habit to ask for a double-check on your resolution by
+someone who is familiar with the code you touched.
+
+[`CE Upstream` merge requests]: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests?label_name%5B%5D=CE+upstream
+
+## Always merge EE merge requests before their CE counterparts
+
+**In order to avoid conflicts in the CE->EE merge, you should always merge the
+EE version of your CE merge request first, if present.**
+
+The rationale for this is that as CE->EE merges are done automatically every few
+hours, it can happen that:
+
+1. A CE merge request that needs EE-specific changes is merged
+1. The automatic CE->EE merge happens
+1. Conflicts due to the CE merge request occur since its EE merge request isn't
+  merged yet
+1. The automatic merge bot will ping someone to resolve the conflict **that are
+  already resolved in the EE merge request that isn't merged yet**
+
+That's a waste of time, and that's why you should merge EE merge request before
+their CE counterpart.
+
+## Avoiding CE->EE merge conflicts beforehand
+
+To avoid the conflicts beforehand, check out the
+[Guidelines for implementing Enterprise Edition features](ee_features.md).
+
+In any case, the CI `ee_compat_check` job will tell you if you need to open an
+EE version of your CE merge request.
+
+### Conflicts detection in CE merge requests
+
+For each commit (except on `master`), the `ee_compat_check` CI job tries to
+detect if the current branch's changes will conflict during the CE->EE merge.
+
+The job reports what files are conflicting and how to setup a merge request
+against EE.
+
+#### How the job works
+
+1. Generates the diff between your branch and current CE `master`
+1. Tries to apply it to current EE `master`
+1. If it applies cleanly, the job succeeds, otherwise...
+1. Detects a branch with the `ee-` prefix or `-ee` suffix in EE
+1. If it exists, generate the diff between this branch and current EE `master`
+1. Tries to apply it to current EE `master`
+1. If it applies cleanly, the job succeeds
+
+In the case where the job fails, it means you should create a `ee-<ce_branch>`
+or `<ce_branch>-ee` branch, push it to EE and open a merge request against EE
+`master`.
+At this point if you retry the failing job in your CE merge request, it should
+now pass.
+
+Notes:
+
+- This task is not a silver-bullet, its current goal is to bring awareness to
+  developers that their work needs to be ported to EE.
+- Community contributors shouldn't be required to submit merge requests against
+  EE, but reviewers should take actions by either creating such EE merge request
+  or asking a GitLab developer to do it **before the merge request is merged**.
+- If you branch is too far behind `master`, the job will fail. In that case you
+  should rebase your branch upon latest `master`.
+- Code reviews for merge requests often consist of multiple iterations of
+  feedback and fixes. There is no need to update your EE MR after each
+  iteration. Instead, create an EE MR as soon as you see the
+  `ee_compat_check` job failing. After you receive the final approval
+  from a Maintainer (but **before the CE MR is merged**) update the EE MR.
+  This helps to identify significant conflicts sooner, but also reduces the
+  number of times you have to resolve conflicts.
+- Please remember to
+  [always have your EE merge request merged before the CE version](#always-merge-ee-merge-requests-before-their-ce-counterparts).
+- You can use [`git rerere`](https://git-scm.com/blog/2010/03/08/rerere.html)
+  to avoid resolving the same conflicts multiple times.
+
+---
+
+[Return to Development documentation](README.md)