There is already some schema and code in place for counters; however it is not used. It was a PoC that received little attention after it was implemented. We need to introduce support for counters as a first class type. This doc describes the schema changes, and design that are needed to implement counters in metrics-core. It does not address the REST API. That is tracked in a separate ticket.
The design doc will be broken down into multiple tickets. This will serve as an umbrella ticket for those tasks.