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tl;dr

Planned upgrades that will impact Stack Overflow & Stack Exchange Network sites including Chat. All sites will be read-only for up to 3 hours beginning shortly after Tuesday, August 23, 2022 at 00:00-03:00 AM UTC (Monday, August 22, 8:00-11:00 PM US/Eastern). You can always view the current status of our network on our status page.

Short Version

There will be a service degradation for up to 3 hours starting at midnight UTC on August 23, 2022 (August 22, 8:00 PM US/Eastern). Although the maintenance window is 3 hours, the actual impact will likely be much shorter lasting around an hour. During that time, 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. Users will not be able to log into Stack Overflow for Teams (free/basic/business tiers) while the site is read-only. A banner on the sites will state that they're read-only for maintenance.

Longer Version of What's Taking Place:

Background

As the current version of Redis we’re using is no longer supported, we are upgrading our Redis instances to v6.2.7.

Our primary Redis 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 generally fail over to our Colorado data center so we can patch, upgrade, and reboot our New York servers.

As part of the upgrade plan, we will take down one of the existing replicas on secondary and upgrade it to the new version, switch all clients to use the new replica, promote the new replica to primary and stop the old primary instance and then repeat the process for all the clusters.

What we'll be doing

During the service interruption, we'll be performing upgrades on the primary Redis servers in NY and the secondary servers in CO that support Stack Overflow, the Stack Exchange Network, and chat. This will allow us to upgrade to the latest and stable version of Redis. We expect that the site will be in a read-only state between 1 hour and 3 hours in total. Once we've done the upgrade, and everything seems to be up and running, we'll take the sites out of read-only.

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    Isn't scheduled maintenance always planned? Aug 20, 2022 at 15:48
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    Unplanned scheduled maintenance could be a fix for an issue that does not need to be done immediately.
    – Josh Zhang StaffMod
    Aug 23, 2022 at 2:41

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