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Bluesky April 2026 Outage Post-Mortem

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Re: Bluesky April 2026 Outage Post-Mortem

#22
post #16
post #15

I don't really understand this architecture, but I thought Bluesky was distributed like Mastodon? How can it have an outage?

Mastodon infra can have outages, too.

It's just confined to one instance if it goes down, not all of Mastodon.

Re: Bluesky April 2026 Outage Post-Mortem

#25
post #17
post #15

I don't really understand this architecture, but I thought Bluesky was distributed like Mastodon? How can it have an outage?

This writeup is useful for backend engineers: https://atproto.com/articles/atproto-for-distsys-engineers The simple answer is that atproto works like the web & search engines, where the apps aggregate from the distributed accounts. So the proper analogy here would be like yahoo going down in 1999.

This is a fantastic write-up, thanks for sharing!

Re: Bluesky April 2026 Outage Post-Mortem

#27

> What I had missed is that we deployed a new internal service last week that sent less than three GetPostRecord requests per second, but it did sometimes send batches of 15-20 thousand URIs at a time. Typically, we'd probably be doing between 1-50 post lookups per request. That’ll do it.

The incredible part about this is because their backend is all TCP/IP they were literally exhausting the ports by leaving all 65k of them in TIME_WAIT, and the workaround was to start randomizing the localhost address to give them another trillion ports or so.

Re: Bluesky April 2026 Outage Post-Mortem

#29

> What I had missed is that we deployed a new internal service last week that sent less than three GetPostRecord requests per second, but it did sometimes send batches of 15-20 thousand URIs at a time. Typically, we'd probably be doing between 1-50 post lookups per request. That’ll do it.

And then they fix the issue by using multiple localhost IPs rather than, perhaps, not sending 15-20 thousand URIs at a time
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