Reduce http_request_queue_time_seconds cardinality + refactor#97
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Reduce http_request_queue_time_seconds cardinality + refactor#97
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This was confusing to read, these values are seconds (floating point) and not miliseconds.
This metric is a mesure of how long a request sits in a queue after it is accepted by a frontend reverse proxy, cache server or load balancer. Dimensions like request method or response code have no bearing on this - since it is only measuring something that happens before our application starts to process the request.
The valid_header_present? method just makes this class harder to use in the callsite. I am happy here for us to return the correct value if we can, and if not return nil
I think this reads better as first non empty header value ...
This can only happen if the clock on the reverse proxy writing the header is skewed against the application server.
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Reduce the cardinality of http_request_queue_time_seconds
Currently we are recording this histogram for each action/controller/method.
This isn't really required since queue time is a function of how many requests (and how long they take to process) at the server level. The currently requested action/controller/method has no impact on this (since at the time we measure queue time we haven't even started processing the request yet).
Also a little refactoring to improve readability, I also added some specs around the middleware.