Warn on missing telegraf relations on the input side

[zxhdaze]

The telegraf charm supports relating to various charms on the input side beyond the simple juju-info interface:

requires:   amqp:     interface: rabbitmq     scope: container   apache:     interface: apache-website     scope: container   elasticsearch:     interface: elasticsearch     scope: container   exec:     interface: telegraf-exec     scope: container   haproxy:     interface: statistics     scope: container   influxdb-api:     interface: influxdb-api   juju-info:     interface: juju-info     scope: container   memcached:     interface: memcache     scope: container   mongodb:     interface: mongodb     scope: container   mysql:     interface: mysql-root   postgresql:     interface: pgsql   redis:     interface: redis     scope: container   sentry:     interface: sentry-metrics     scope: container

We should warn whenever those relations are missing as we're missing the chance of generating more useful metrics.

Note that at least in some case both the juju-info and the more specific relation need to be present. See the telegraf readme for details.

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Imported from Launchpad using lp2gh.

• date created: 2022-09-07T18:14:25Z

• owner: aieri

• assignee: None

• the launchpad url

[zxhdaze]

(by eric-chen) This charm is no longer being actively maintained