client/metadata: fix crasher caused by AllowStale = false #16549
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Fixes #16517 Given a 3 Server cluster with at least 1 Client connected to Follower 1: If a NodeMeta.{Apply,Read} for the Client request is received by Follower 1 with `AllowStale = false` the Follower will forward the request to the Leader. The Leader, not being connected to the target Client, will forward the RPC to Follower 1. Follower 1, seeing AllowStale=false, will forward the request to the Leader. The Leader, not being connected to... well hoppefully you get the picture: an infinite loop occurs.
lgfa29
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Mar 20, 2023
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| // | ||
| // BREAKING: This method will have the following signature in 1.6.0 | ||
| // func (a *Allocations) Restart(allocID string, taskName string, allTasks bool, w *WriteOptions) (*WriteMeta, error) { |
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I can't believe how many hints we were given that this would happen. I know I even hit it in the e2e cluster at least once but couldn't reproduce it and just assumed it was some terrible thing I had done to my e2e cluster.
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I had never heard of that before and love it!
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Fixes #16517
Given a 3 Server cluster with at least 1 Client connected to Follower 1:
If a NodeMeta.{Apply,Read} for the Client request is received by Follower 1 with
AllowStale = falsethe Follower will forward the request to the Leader.The Leader, not being connected to the target Client, will forward the RPC to Follower 1.
Follower 1, seeing AllowStale=false, will forward the request to the Leader.
The Leader, not being connected to... well hoppefully you get the picture: an infinite loop occurs.
Manually testing looks good, but
automated testing is still WIP.Update: I'm pretty pleased with how the manual test turned out! It's pretty big but reliably exercises the bug without the patch. With the fix the test runs in <400ms locally which isn't bad for running 7 agents and waiting for each one to become ready!
If you're feeling brave (or like watching the world burn), you can exercise the bug by commenting out one of the
AllowStale = truelines and running the test withgo test -v -run NodeMetain thenomad/directory.I highly recommend doing that in a container or VM so you don't mess up your machine. I used: