If you have multiple web/rails nodes 15.1 is an additional required step. See 15.2.0 Upgrade Notes
If you have npm packages in your package registry, you must upgrade to 16.1 first.
16.0 is a required upgrade step for instances with 30k Users
16.2 is a required update step for Instances with large pipeline variables history. See 16.2.0 Upgrade Notes
With GitLab 16.0 all access tokens have a forced expiry date. Users upgrading after July 24, 2024, from a pre-16.0 version of GitLab to the latest patch release of Version 16.0 or later will not have an expiration date set for tokens that didn't have one previously. After deploying 16.0 (or a later release) any non-expiring access tokens will expire 1 year from your first 16.x or above deployment date. Guide to Identify
If you upgrade the operating system on which PostgreSQL runs, an upgrade of locale data changes in glibc 2.28 and later might corrupt your database indexes. See upgrading operating systems for PostgreSQL guide for options to avoid this issue
With GitLab 17.7, the Linux package upgrades OpenSSL from from v1.1.1w to v3.0.0. Before upgrading, use the OpenSSL 3 guide to identify and assess the compatibility of your external integrations.