replicaset not always available in relation

[Casey Marshall]

I've noticed that 'replicaset' is available in the database relation when a replica set has already been explicitly set, and then a relation to mongodb:database is established.

However, I've encountered some problems:

1. The default 'myset' replicaset name is not set on the relation, if I first relate to mongodb:database and then add some units.

2. If I change the replica set name with something like 'juju set mongodb replicaset=foo' after relating to mongodb:database , the relation changed hook does not fire.

I found both of these surprising behaviors. I can work around them by breaking the relation and adding it -- or restricting the order of Juju operations -- so that the mongodb will set the replicaset name on the relation.

However, I am concerned this is fragile behavior.

Are these limitations of Juju, or a defect in the charm that could be improved? My application requires the replicaset name if replication is used with MongoDB (due to driver limitations).

Thanks!
Casey

[Matthew Williams (mattyw)]

It does appear that the reverse is also true. That a mongodb reporting

> rs.status()
{ "ok" : 0, "errmsg" : "not running with --replSet" }

Can report via the charm a replicaset name

[mahmoh (mahmoh)]

I've also hit this with an Autopilot deployment on arm64:

mongodb/1 error idle 1.24.6 0/lxc/5 27017/tcp,27019/tcp,27021/tcp,28017/tcp 172.16.9.144 hook failed: "replica-set-relation-changed"

...
2015-10-25 04:52:20 INFO start mongodb start/running, process 3339
2015-10-25 04:52:21 INFO juju-log port_check: Unable to connect to 172.16.9.131:27017/TCP.
2015-10-25 04:52:21 INFO juju-log port_check: Exception: [Errno 111] Connection refused
2015-10-25 04:52:21 INFO juju-log restart_mongod: Waiting for MongoDB to be ready (0/5)
2015-10-25 04:52:31 INFO start mongodb start/running, process 3339
2015-10-25 04:52:31 INFO juju-log port_check: 172.16.9.131:27017/TCP is open
2015-10-25 04:52:31 INFO start mongodb start/running, process 3339
2015-10-25 04:52:32 INFO juju-log port_check: 172.16.9.131:27017/TCP is open
2015-10-25 04:52:32 INFO juju-log start_hook returns: True
2015-10-25 04:58:24 INFO juju-log replica-set:8: replica_set_relation_joined-start
2015-10-25 04:58:25 INFO juju-log replica-set:8: my_hostname: 172.16.9.131
2015-10-25 04:58:25 INFO juju-log replica-set:8: my_port: 27017
2015-10-25 04:58:25 INFO juju-log replica-set:8: my_replset: myset
2015-10-25 04:58:26 INFO juju-log replica-set:8: my_install_order: 0
2015-10-25 04:58:26 INFO juju-log replica-set:8: enable_replset: trying to get lock on: /etc/init/mongodb.conf
2015-10-25 04:58:26 DEBUG juju-log replica-set:8: enable_replset: lock acquired
2015-10-25 04:58:26 DEBUG juju-log replica-set:8: enable_replset: --replset not preset, enabling
2015-10-25 04:58:27 INFO juju-log replica-set:8: regex_sub
2015-10-25 04:58:27 DEBUG juju-log replica-set:8: update_file: /etc/init/mongodb.conf
2015-10-25 04:58:27 DEBUG juju-log replica-set:8: enable_replset will return: True
2015-10-25 04:58:27 DEBUG juju-log replica-set:8: Restarting mongodb after config change (enable replset)
2015-10-25 04:58:28 INFO replica-set-relation-joined mongodb stop/waiting
2015-10-25 04:58:28 INFO replica-set-relation-joined mongodb start/running, process 3566
2015-10-25 04:58:28 INFO replica-set-relation-joined mongodb start/running, process 3566
2015-10-25 04:58:28 INFO juju-log replica-set:8: port_check: Unable to connect to 172.16.9.131:27017/TCP.
2015-10-25 04:58:28 INFO juju-log replica-set:8: port_check: Exception: [Errno 111] Connection refused
2015-10-25 04:58:28 INFO juju-log replica-set:8: restart_mongod: Waiting for MongoDB to be ready (0/5)
2015-10-25 04:58:39 INFO replica-set-relation-joined mongodb start/running, process 3566
2015-10-25 04:58:39 INFO juju-log replica-set:8: port_check: 172.16.9.131:27017/TCP is open
2015-10-25 04:58:39 INFO replica-set-relation-joined mongodb start/running, process 3566
2015-10-25 04:58:39 INFO juju-log replica-set:8: port_check: 172.16.9.131:27017/TCP is open
2015-10-25 04:58:40 INFO juju-log replica-set:8: replica_set_relation_joined-finish
2015-10-25 04:58:43 INFO juju-log replica-set:8: replica_set_relation_changed-start
2015-10-25 04:58:43 DEBUG juju-log replica-set:8: local unit: 172.16.9.131, joining_unit: 172.16.9.144
2015-10-25 04:58:44 INFO juju-log replica-set:8: Initializing replicaset
2015-10-25 04:58:44 DEBUG juju-log re...

[Mario Splivalo (mariosplivalo)]

Hi, Casey.

Just for clarification:

1. For the 'myset' name, you would like that one set inside relaction, regardless of replicaset being formed or not? The charm does not initialize replicaset is there is only a single unit of mongodb deployed.

2. I'm assuming that the reason of relation-changed hook not firing is because you can not (easily) change the replicaset name once replicaset has been initialized - if one wishes to change the replicaset name system collections need to be updated and mongod stopped.
If I change the replica set name with something like 'juju set mongodb replicaset=foo' after relating to mongodb:database , the relation changed hook does not fire.
What would be, in your opinion, desired behavior here?