tl;dr
Planned service interruption that will impact all Stack Overflow & Stack Exchange sites, Stack Overflow for Teams (free/basic/business tiers), and Chat. All sites may be read-only for up to 60 minutes beginning shortly after Wednesday, 21 September, 2022 at 00:30 UTC (Tuesday, September 20 at 8:30 PM EDT). Enterprise cloud hosted instances will not be impacted.
Short version:
There will be a service degradation for up to 60 minutes starting at 00:30 UTC on 21 September, 2022 (September 20 at 8:30 PM US Eastern Daylight Time). During that period, questions and answers will still display, and ads will still display. However, the site will be "read only" — i.e. people won't be able to post, edit or vote on questions/comments/answers, reputation won't change, etc. Stack Overflow for Teams users who are logged in to a Team will remain logged into that Team and can view that Team in read-only mode. Stack Overflow for Teams users (free/basic/business tiers) who are not already logged into a Team will be unable to log in while that Team is in read-only mode. 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:
Background
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 disruptive maintenance on the primary servers, we need to failover to another server so we can patch, upgrade, and reboot them. When we perform patching for our database servers, we generally patch secondary servers first, then fail over the primary server to a patched node, then patch the former primary (post-failover secondary).
Like other recent database failovers, we place the site in read-only mode as part of this process, as we continue to troubleshoot a performance issue we have during failover. We have made changes to the number of databases per SQL Server Availability Group, which we believe will help mitigate the performance issue, and we will be testing this potential fix during the maintenance window.
What we'll be doing
During the service interruption, we'll be performing failovers from the primary database servers to the already-patched secondary servers in New York for the SQL Servers that support Stack Overflow, the Stack Exchange Network, Stack Overflow for Teams, and Chat. This will allow us to patch the former primary SQL Server with the latest Windows & SQL Server patches.
We expect that the sites will be in a read-only state for up to 60 minutes, however we like to leave a little room, hence the longer maintenance window. Once we've done the failover, and everything seems to be up and running, we'll take the sites out of read-only mode.
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.
