Incorrect usage of emit() or incorrect comment

[carlcsaposs-canonical]

This block of code does not behave as the comment describes

opensearch-operator/lib/charms/opensearch/v0/opensearch_base_charm.py

Lines 471 to 476 in b0208dc

	# since when an IP change happens, "_on_peer_relation_joined" won't be called,
	# we need to alert the leader that it must recompute the node roles for any unit whose
	# roles were changed while the current unit was cut-off from the rest of the network
	self.on[PeerRelationName].relation_joined.emit(
	self.model.get_relation(PeerRelationName)
	)

relation-joined will only be emitted on that unit (where

opensearch-operator/lib/charms/opensearch/v0/opensearch_base_charm.py

Line 466 in b0208dc

if self.opensearch_config.update_host_if_needed():

evaluates to True)

And that unit will immediately return

opensearch-operator/lib/charms/opensearch/v0/opensearch_base_charm.py

Lines 294 to 297 in b0208dc

	def _on_peer_relation_joined(self, event: RelationJoinedEvent):
	"""Event received by all units when a new node joins the cluster."""
	if not self.unit.is_leader():
	return

More info:

Note that the emission of custom events is handled immediately. In other words, custom events are not queued, but rather nested. For example:

1. Main hook handler (emits custom_event_1)
2.   Custom event 1 handler (emits custom_event_2)
3.     Custom event 2 handler
4.   Resume custom event 1 handler
5. Resume main hook handler

https://ops.readthedocs.io/en/latest/#ops.BoundEvent.emit

[github-actions]

https://warthogs.atlassian.net/browse/DPE-3828

[carlcsaposs-canonical]

Potential solution: instead of emitting custom event, write something to unit peer databag (and ensure peer databag is updated [i.e. don't write data that's already there]) to trigger a peer-relation-changed event on all other units

[Mehdi-Bendriss]

This looks like a bug indeed. Thanks!

In this case, I don't think we unfortunately can get away from emitting the event, in case the current unit is the elected leader unit - which will then not receive a peer-rel-changed event if the data is stored in its unit data bag..

I believe the fix is a mix of both approaches, something along the lines of:

if self.unit.is_leader():
    self.on[PeerRelationName].relation_joined.emit( 
        self.model.get_relation(PeerRelationName) 
    )
self.peers_data.put(
    Scope.UNIT, "updated_at", datetime.now().timestamp()
)