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Make a backup of the existing elasticsearch database.
Make a cloned ES server under a new hostname.
Upgrade cloned ES server to 2.x.
Reindex everything through their migration plugin.
Make another database backup.
Upgrade cloned ES server to 5.x.
At this point, the server’s data will become start becoming stale, and we should ideally update clients in short order.
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Update devstack with a script to do the above server upgrade.
Start landing PRs to update client services to elasticsearch-py 5.x in concert with config changes that point at the new ES hostname.
Message out the changes, letting people know they should update devstack.
Cleanup
Document the change and how to upgrade servers in our Open edX release notes.
Decommision old ES 1.x servers once all services are upgraded.