How can GitKraken’s branch synchronization be used to migrate a small application to a new environment without downtime?

Our team needs to move a small Node.js application from a legacy server to a container‑based environment while keeping the service continuously available for users. We intend to use GitKraken’s branch synchronization feature to keep a preparation branch in sync with the main branch across repositories, allowing us to test the new deployment setup without affecting the live version.

Because the application cannot afford any downtime, we are unsure how to configure the synchronization so that only commits that have passed our CI pipeline are reflected, what precautions we should take before merging the prepared branch into production, and how we can verify that the cut‑over occurred seamlessly without exposing incomplete code or causing errors.

How can we set up the branch sync to include only CI‑approved commits? What checks should be performed before triggering the merge of the sync branch into the production branch? How do we confirm that the cut‑over resulted in zero downtime and no user‑visible errors?