, 6 tweets, 2 min read Read on Twitter
Several reporters are asking me for insight on the FB outage. I have none, other than that outages on massive distributed systems can sometimes follow this pattern:
1) A human engineer makes a small config change. It goes into test environment and everything is ok, so the change makes its way to production.
2) Config change has unintended side-effects that only express in production, perhaps due to scale or a mismatch with the test environment. Things start to go haywire, and failures compound as critical services timeout and queues lengthen.
3) Fortunately, this company is staffed by real adult engineers who considered this possibility, so there is an automated or semi-automated process to roll-back to the last known good state. This automated agent is dispatched to deal with the anomaly.
4) Unfortunately, the automated system doesn't know how to handle the problem, and gets stuck in some kind of loop that causes more damage. Humans have to step in, stop it, and restart a complex web of interdependent services on hundreds of thousands of systems.
5) Humans win, but after paying a significant cost. The system, now rebooted into its new incarnation, is safe for now. But how long can the peace between man and machine hold?
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