Issues due to direct dependency on prom-client library when used for nodejs cluster

[pp05]

Hello @lance
First of all thanks for the https://github.com/nodeshift/opossum library which seems to have work pretty well for us so far as a circuit breaker library. 👍
We have also opted to use the https://github.com/nodeshift/opossum-prometheus for monitoring the circuit breakers.
Our nodejs application runs on a cluster mode with a configurable number of worker threads.

• When we tested we found that opossum-prometheus collects the metrics per worker thread
• Where as in a cluster one would be probably interested in the aggregated metrics of the cluster
• Which means doing something like this https://github.com/siimon/prom-client/blob/master/example/cluster.js
  When we brought in the direct dependency of the prom-client library in our application we noticed the data coming back from the prom-client AggregateRegistry::getClusterMetrics() was in coherent and not the aggregated value as expected.
  On further debugging we found that the worker threads were responding multiple times to a single message from the cluster master.

The root cause seems to be the multiple dependency on prom-client brought in because of direct dependency of opossum-prometheus & our own dependency to use the AggregateRegistry.
This seems to be a known problem e.g. if you notice this one slanatech/swagger-stats#114 express-prom-bundle have made a fix to the same effect and made prom-client a peer dependency.

A similar approach here would work as well.
I might give it a shot and open a PR for this as well a bit later when I have some time.

[lance]

@pp05 thanks for that detailed explanation. If you have the time and energy for a PR it would definitely be appreciated!

[iamelevich]

You can check my implementation with no direct dependency on prom-client, so you can provide that you need https://github.com/iamelevich/opossum-prometheus