Update: The maintenance went as planned.
tl;dr; Planned service interruption that will impact all Stack Overflow/Stack Exchange sites, Jobs, Chat, and Teams. All sites may be read-only for up to 15 minutes on Saturday March 27, 2021 at 1:00 UTC (Friday March 26th 9 PM US/EDT). Enterprise cloud hosted instances will not be impacted.
There will be a service degradation for up to 15 minutes 1:00 UTC on March 27th, 2021 (March 26th 9:00 PM US/EDT). 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. This should minimize the disruption to the majority of casual readers. We will display a banner on the sites stating we'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.
What we'll be doing
During the service interruption, we'll be performing a failover from the primary location to a secondary server in New York. This allows us to patch the former primary SQL Server and apply Windows updates to the server. By putting the sites in a read-only state, we reduce the chance of data loss and the entire process becomes faster.
We expect that the site will be in a read-only state for less than 15 minutes. 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.