• Fixes Panic in libnetwork during daemon start (panic: runtime error: index out of range [0] with length 0) #45057

The (*network).ipamRelease function nils out the network's IPAM info fields, putting the network struct into an inconsistent state. The network-restore startup code panics if it tries to restore a network from a struct which has fewer IPAM config entries than IPAM info entries. Therefore (*network).delete contains a critical section: by persisting the network to the store after ipamRelease(), the datastore will contain an inconsistent network until the deletion operation completes and finishes deleting the network from the datastore. If for any reason the deletion operation is interrupted between ipamRelease() and deleteFromStore(), the daemon will crash on startup when it tries to restore the network.

Updating the datastore after releasing the network's IPAM pools may have served a purpose in the past, when a global datastore was used for intra-cluster communication and the IPAM allocator had persistent global state, but nowadays there is no global datastore and the IPAM allocator has no persistent state whatsoever. Remove the vestigial datastore update as it is no longer necessary and only serves to cause problems. If the network deletion is interrupted before the network is deleted from the datastore, the deletion will resume during the next daemon startup, including releasing the IPAM pools.

- What I did

- How I did it

- How to verify it
Race a network delete with shutting down the daemon. Verify that the daemon starts back up without panicking.

$ docker network create foo
$ docker network rm foo & sleep 0.01; pkill -TERM dockerd

You will have hit the race window if the docker network rm command logs an error indicative of the daemon shutting down before the API request completes, such as

error during connect: Delete http://%2Fvar%2Frun%2Fdocker.sock/v1.30/networks/foo: EOF

and on next startup, the daemon logs an INFO message Removing stale network foo.

- Description for the changelog

• Fixed an issue which could corrupt the daemon state, crashing on next start if the daemon is terminated while a container network is being deleted

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