Error message for "cluster-relation-change" hook failure is unclear for user

[a-velasco]

Issue

Mongos' message hook failed: "cluster-relation-changed" and error status are not very informative for an end user.

Example

On a sharded cluster, I deployed data-integrator without any config specifications:

juju deploy data-integrator
juju deploy mongos --channel 6/edge

which leaves it in a blocked state.

While still blocked, I tried to integrate it with mongos:

juju integrate mongos data-integrator

This gave the following juju status output for mongos:

App              Version  Status   Scale  Charm            Channel  Rev  Exposed  Message
config-server             active       1  mongodb          6/beta   149  no       Primary
data-integrator           blocked      1  data-integrator  stable    19  no       Please specify either topic, index, or database name
mongos                    error        1  mongos           6/edge     5  no       hook failed: "cluster-relation-changed"
shard0                    active       1  mongodb          6/beta   149  no       Primary
shard1                    active       1  mongodb          6/beta   149  no       Primary

Solution

As suggested by @MiaAltieri, the status for this event could instead go into blocked with a more explanatory error message.