[nexus] Make snapshot-create saga unwind-safe#2093
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smklein
commented
Dec 26, 2022
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| #[cfg(test)] | ||
| mod test { | ||
| pub(crate) mod test { |
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I'm mostly modifying this so I can re-use some of the test functions which validates "disk creation doesn't leave detritus".
Most of these checks are identical for snapshot creation.
smklein
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Dec 26, 2022
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| // Unfortunately, for our idempotency checks, checking for a "clean | ||
| // slate" gets more expensive when we need to compare region allocations | ||
| // between the disk and the snapshot. If we can undo the snapshot | ||
| // provisioning AND delete the disk together, these checks are much | ||
| // simpler to write. |
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This detail matters - basically, it's easy to check "nothing exists in the DB", and harder to check "the state which was provisioned for a disk exists and matches, but nothing else was added".
Unwinding the snapshot AND deleting the disk gets us back to the simpler "nothing should exist" state.
smklein
commented
Dec 27, 2022
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| // NOTE: If we later create a volume record and delete it, the | ||
| // running snapshot may be deleted (see: | ||
| // ssc_create_volume_record_undo). | ||
| // | ||
| // To cope, we treat "running snapshot not found" as "Ok", since it | ||
| // may just be the result of the volume deletion steps completing. | ||
| .or_else(|err| match err { | ||
| ErrorResponse(r) if r.status() == StatusCode::NOT_FOUND => { | ||
| Ok(()) | ||
| } | ||
| _ => Err(err), | ||
| })?; |
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I found this a little quirky; figured I'd call it out.
- If we haven't run the later "volume creation" undo step, we need to cleanup this running snapshot.
- If we have run the later "volume creation" undo step, it's already gone
leftwo
approved these changes
Dec 28, 2022
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Part of #2052