I haven't dug particularly deeply. However if I do
charm pull ceilometer
I get: cs:ceilometer-24
And then dig into the contents of:
charmhelpers/contrib/peerstorage/__init__.py
I see that it has a function:
def leader_get():
which looks like it is supposed to be a compatibility function, so that
old versions of the charm can just use peer relation settings to
coordinate, and new versions of the charm can use leader-set and leader-
get directly. However, if I'm reading through the code it does:
if attribute:
...
# If attribute not present in leader db, check if this unit has set
# the attribute in the peer relation
if not leader_settings:
peer_setting = _relation_get(attribute=attribute, unit=local_unit(),
rid=rid)
if peer_setting:
leader_set(settings={attribute: peer_setting})
leader_settings = peer_setting
Nothing in there does any sort of check for "is_leader". It is possible
that the original call to "leader_get" itself is done inside a
"is_leader" check, but this function appears to be trying to "look for
settings that might have been set by a leader, but fall back to a peer
relation, and if found in a peer relation set them in the leader
settings" which would only be safe to do *as* the leader.
Note also that peerstorage.__init__.py has a "relation_get" function
which directly calls "leader_get" which (as noted) might try to call
leader_set.
Similarly the function "peer_retrieve" tries to call relation_get, which may
call leader_get which may ultimately call 'leader_set'.
There may be other issues, but the code as written appears to be unsafe
to use.
It may be that a better writing would trap inside "leader_get" and only
attempt to do a migration if "is_leader()" returned True?
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https://bugs.launchpad.net/bugs/1654116
Title:
Attempts to write leadership settings when not the leader during
relation-changed hooks
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