go-http-instrument

README

Simple Go net/http instrumentation for Prometheus

This library is a fork of Prometheus golang_client/prometheus/http handler proxy: https://github.com/prometheus/client_golang/blob/master/prometheus/http.go#L152

The documentation of InstrumentHandler mentions the following problems:

 - It uses Summaries rather than Histograms. Summaries are not useful if
 aggregation across multiple instances is required.

 - It uses microseconds as unit, which is deprecated and should be replaced by
 seconds.

 - The size of the request is calculated in a separate goroutine. Since this
 calculator requires access to the request header, it creates a race with
 any writes to the header performed during request handling.
 httputil.ReverseProxy is a prominent example for a handler
 performing such writes.

The first two problems are mitigated. The third one is hard and as a moment of writing I didn't find a need to implement it, thus for a sake of race condition detection it was disabled.

Additionally a gauge inflight_requests was added.

The histogram buckets:

    []float64{0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7,
              0.8, 0.9, 1., 2., 5., 10., 20., 30., 40., 50.}

Get the library:

go get github.com/orian/go-http-instrument/instrumentation

For developers

For a testing purposes I've prepared a super simple http server to run in Docker.

The bin directory contains a trivial binary. To compile:

cd bin
CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o simpleserver simpleserver.go

Than one needs to execute:

docker build -t instrument/demoserver .
docker run --rm -it --net promnet -p 8080:8080 \
    --name httpexample instrument/demoserver

Prometheus:

docker pull prom/prometheus

docker run --rm -it -p 9090:9090 --net promnet \ 
    --name prom -v $PWD/prom/prometheus.yaml:/etc/prometheus/prometheus.yml \
    prom/prometheus

To see changes in metrics run some queries. The demo server accepts two query params:

• dur - how long the request should take.
• code - what HTTP status code to return.

curl -v "localhost:8080/" &
curl -v "localhost:8080/?code=404&dur=1.5" &
curl -v "localhost:8080/?code=404&dur=15" &
curl -v "localhost:8080/?dur=105" &
curl -v "localhost:8080/?code=500&dur=50" & 
curl -v "localhost:8080/?dur=34" &
curl -v "localhost:8080/?dur=20" &