This work is now complete
Planned service interruption that will impact all Stack Overflow & Stack Exchange sites, Jobs, and Chat. All sites may be read-only for up to 30 minutes beginning shortly after Thursday, 16 December at 01:30 UTC (Wednesday, December 15 at 8:30 PM US/EST). Enterprise cloud hosted instances will not be impacted.
There will be a service degradation for up to 30 minutes starting at 01:30am UTC on 16 December, 2021 (December 15 at 8:30 PM US/EST). During that time, questions and answers will still display, job listings will still work, and job ads will still display. However, the site will be "read only" — i.e. people won't be able to add/edit new job listings, apply for jobs, post, edit or vote on questions/comments/answers, reputation won't change, etc. Users will not be able to log into Stack Overflow for Teams (free/basic/business tiers) while the site is read only. This should minimize the disruption to the majority of casual readers. We will display a banner on the sites stating that they're read-only for maintenance.
Longer Version of What's Taking Place:
Our primary database servers – which power Stack Overflow, Stack Exchange, Chat, and other things – run out of New York (really New Jersey) with our secondary location in Colorado. When we need to perform maintenance on the primary servers, we need to failover to another server so we can patch, upgrade, and reboot them.
When we do patching for our database servers, we generally patch secondary servers, failover the primary server to a patched node, then patch the former primary (post-failover secondary).
What we'll be doing
During the service interruption, we'll be performing failovers from the primary database servers to the secondary servers in New York for the SQL Servers that support Stack Overflow, the Stack Exchange Network, jobs, and chat. This will allow us to patch the former primary SQL Server with the latest Windows & SQL Server patches.
We expect that the site will be in a read-only state for between 15 and 30 minutes in total. Once we've done the failover, and everything seems to be up and running, we'll take the sites out of read-only.
Questions or concerns?
Please post a comment or answer below; I'll do my best to address any concerns between now and the maintenance window.