[25.0 backport] libnetwork: fix flaky Swarm service DNS #50230
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When libnetwork receives a watch event for a driver table entry from NetworkDB it passes the event along to the interested driver. This code contains a subtle bug: update events from NetworkDB are passed along to the driver as Delete events! This bug was lying dormant as driver-table entries can only be added by the driver, not updated. Now that NetworkDB broadcasts an UpdateEvent to watchers if the entry is already known to the local NetworkDB, irrespective of whether the event received from the remote peer was a CREATE or UPDATE event, the bug is causing problems. Whenever a remote node replaces an entry in the overlay_peer_table but the intermediate delete state was not received by the local node, the new CREATE event would be translated to an UpdateEvent by NetworkDB and subsequently handled by the overlay driver as if the entry was deleted! Bubble table UPDATE events up to the network driver as Update events. Signed-off-by: Cory Snider <[email protected]> (cherry picked from commit a7f01d2) Signed-off-by: Cory Snider <[email protected]>
robmry
approved these changes
Jun 19, 2025
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- What I did
- How I did it
When libnetwork receives a watch event for a driver table entry from NetworkDB it passes the event along to the interested driver. This code contains a subtle bug: update events from NetworkDB are passed along to the driver as Delete events! This bug was lying dormant as driver-table entries can only be added by the driver, not updated. Now that NetworkDB broadcasts an UpdateEvent to watchers if the entry is already known to the local NetworkDB, irrespective of whether the event received from the remote peer was a CREATE or UPDATE event, the bug is causing problems. Whenever a remote node replaces an entry in the overlay_peer_table but the intermediate delete state was not received by the local node, the new CREATE event would be translated to an UpdateEvent by NetworkDB and subsequently handled by the overlay driver as if the entry was deleted!
Bubble table UPDATE events up to the network driver as Update events.
- How to verify it
🤷
- Human readable description for the release notes
- Fix an issue which made DNS service discovery for Swarm services unreliable- A picture of a cute animal (not mandatory but encouraged)