cassandra_username became juju_None

[Brian Murray]

I've been working on a mojo specification for the Ubuntu Error Tracker, you can find my work at:

https://code.launchpad.net/~brian-murray/canonical-mojo-specs/initial-error-tracker

The devel stage of the spec uses apache cassandra, not dse. When I have been using that stage I encountered a situation where e-t-daisy-app has a "good" cassandra username and e-t-errors-app does not. Log from e-t-errors-app:

2016-03-08 16:20:28 INFO db-relation-changed + REL_ID=db:17
2016-03-08 16:20:28 INFO db-relation-changed ++ relation-get -r db:17 username e-t-cassandra/0
2016-03-08 16:20:28 INFO db-relation-changed + cassandra_username=juju_None
2016-03-08 16:20:28 INFO db-relation-changed + save_setting cassandra_username juju_None
2016-03-08 16:20:28 INFO db-relation-changed + key=cassandra_username
2016-03-08 16:20:28 INFO db-relation-changed + value=juju_None

And the log from e-t-daisy-app:

2016-03-08 16:20:28 INFO db-relation-changed ++ relation-ids db
2016-03-08 16:20:28 INFO db-relation-changed + REL_ID=db:16
2016-03-08 16:20:28 INFO db-relation-changed ++ relation-get -r db:16 username e-t-cassandra/0
2016-03-08 16:20:28 INFO db-relation-changed + cassandra_username=juju_e-t-daisy-app
2016-03-08 16:20:28 INFO db-relation-changed + save_setting cassandra_username juju_e-t-daisy-app
2016-03-08 16:20:28 INFO db-relation-changed + key=cassandra_username
2016-03-08 16:20:28 INFO db-relation-changed + value=juju_e-t-daisy-app

This also happened with e-t-retracer-app:

2016-03-08 16:20:29 INFO db-relation-changed ++ relation-ids db
2016-03-08 16:20:29 INFO db-relation-changed + REL_ID=db:18
2016-03-08 16:20:29 INFO db-relation-changed ++ relation-get -r db:18 username e-t-cassandra/0
2016-03-08 16:20:29 INFO db-relation-changed + cassandra_username=juju_None
2016-03-08 16:20:29 INFO db-relation-changed + save_setting cassandra_username juju_None
2016-03-08 16:20:29 INFO db-relation-changed + key=cassandra_username
2016-03-08 16:20:29 INFO db-relation-changed + value=juju_None

I've not had this issue using the DSE version and staging version of the spec.

[Stuart Bishop (stub)]

I think this is a race, and is just less likely to occur with DSE due to different timings.

[Stuart Bishop (stub)]

It appears that if the relation-joined hook is run early enough on the Cassandra unit, there are no related units yet joined and the remote service name is unknown. We need to check for this case and when it occurs do nothing until a later hook.