prometheus-wai-middleware

Use this library to track HTTP status code counts and request handling times in your web application. We depend on prometheus rather than prometheus-client (see here if you use prometheus-client). The metrics are

• http_requests_total with codes labeled by http_response_code
• http_request_duration_milliseconds

Here is an example of the metrics generated:

# TYPE http_request_duration_milliseconds histogram
http_request_duration_milliseconds_bucket{app="example_server",le="1.0"} 2.0
...
http_request_duration_milliseconds_sum{app="example_server"} 0.0
http_request_duration_milliseconds_count{app="example_server"} 2
# TYPE http_requests_total counter
http_requests_total{app="example_server",http_response_code="100"} 0
...
http_requests_total{app="example_server",http_response_code="200"} 1
...

Examples

See exec/Main.hs for an example of how to instrument a Wai Application. With a bit more legwork you can also instrument individual endpoints. For each endpoint you wish to instrument, simply create an ApplicationMetrics value using applicationMetrics and update it with countStatusCode and observeLatency.