Kafka reporter

[nbozic-zz]

We are starting to develop Sentinel infra to accept measurements. Can you double check KafkaReport is it ok after changes we did and can you check if it will work when we spin up Sentinel infra.

[nbozic-zz]

Check #228 as well while you review this

[nbozic-zz]

Also #227 which Nikola added

[mgobec]

Currently measurement is reported as:

• topic: measurement name
• partition key: hostname
• value: measurement json representation

At this moment it looks ok for the initial metrics push to Sentinel. Higher level of configurability should be considered going forward (topics, partitioning, serialization,...)

[nivancevic]

MetricsModule uses actual Cassandra metrics' names as destination Kafka topic name. It means that dozens of Kafka topics and consumers needed to exists in order to receive all measurements. Should we change the module behavior or modify the kafka reporter?

[mgobec]

We need to update metrics module to generate complex measurements instead of simple measurement for each metric collected.

[nivancevic]

Created a new issue for complex measurements in Metrics module (#246).