About known issues with GitHub Enterprise Server upgrades
GitHub is aware of the following issues that could impact upgrades to new releases of GitHub Enterprise Server. For more information, see "Known issues" in the GitHub Enterprise Server release notes.
GitHub strongly recommends regular backups of your instance's configuration and data. Before you proceed with any upgrade, back up your instance, then validate the backup in a staging environment. For more information, see "Configuring backups on your instance" and "Setting up a staging instance."
Elasticsearch Upgrade
As part of upgrading GitHub Enterprise Server to version 3.13 or later, the Elasticsearch service will be upgraded. GitHub strongly recommends following the guidance in "Preparing for the Elasticsearch upgrade in GitHub Enterprise Server 3.13."