Gather metrics from all connected subscribers #50
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joedixon
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This was referenced Apr 19, 2024
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This PR aims to solve an issue with gathering metrics when running Reverb on multiple servers.
In a scenario when a request is made to
/connectionsand with Reverb running in a load balanced configuration, at the moment, only the connections for the server selected to handle that request will be counted.To resolve this, we can use the existing Redis pub/sub implementation to ask the other servers to report their status.
When a request to any of the metrics endpoints is made, we delegate to the
MetricsHandlerclass. When running in a multi-server setup, the handler will publish an event with typemetricswhich signals all subscribers to gather their results for the given metric and publish their response using themetrics-retrievedevent. When the initial request is made, the total number of subscribers is stored and used to track responses. When all responses are received, the metrics are merged and returned in the HTTP response.One big difference here is the need for promises. Due to having to wait for responses from all subscribers (or a timeout in case of any issue), there is a requirement to only return the response when the promise resolves.