* cmd: update prometheus.NewProcessCollector args.
There's a new struct `prometheus.ProcessCollectorOpts` that is expected
to be used as the sole argument to `prometheus.NewProcessCollector`. We
don't need to specify `os.Getpid` as the `PidFn` of the struct because
the default is to assume `os.Getpid`. Similarly we don't need to set the
namespace to `""` explicitly, it is the default.
* SA: reimplement db metrics as custom collector.
The modern Prometheus golang API supports translating between legacy
metric sources on the fly with a custom collector. We can use this
approach to collect the metrics from `gorp.DbMap`'s via the `sql.DB`
type's `Stats` function and the returned `sql.DbStats` struct.
This is a cleaner solution overall (we can lose the DB metrics updating
go routine) and it avoids the need to use the now-removed `Set` method
of the `prometheus.Counter` type.
* test: Update CountHistogramSamples.
The `With` function of `prometheus.HistogramVec` types we tend to use as
the argument to `test.CountHistogramSamples` changed to return
a `prometheus.Observer`. Since we only use this function in test
contexts, and only with things that cast back to
a `prometheus.Histogram` we take that approach to fix the problem
without updating call-sites.
This vendors the Prometheus client code, and exports metrics on the debug port, under `/metrics`.
This will currently export just the default metrics, like `go_goroutines`, `process_cpu_seconds_total`, `process_open_fds`, and `process_resident_memory_bytes`. Later work will start exporting Boulder-specific metrics, but this will allow Ops to start configuring scraping of Prometheus metrics in production.
Tests pass:
```
$ git diff master Godeps/ | sed -ne 's/^+.*ImportPath": "//p' | tr -d '",' | xargs go test
ok github.com/beorn7/perks/quantile 0.562s
ok github.com/matttproud/golang_protobuf_extensions/pbutil 0.003s
ok github.com/prometheus/client_golang/prometheus 34.418s
ok github.com/prometheus/client_golang/prometheus/promhttp 0.003s
? github.com/prometheus/client_model/go [no test files]
ok github.com/prometheus/common/expfmt 0.019s
ok github.com/prometheus/common/internal/bitbucket.org/ww/goautoneg 0.002s
ok github.com/prometheus/common/model 0.003s
ok github.com/prometheus/procfs 0.008s
```
Part of #2284
milgradesec
Daniel McCarney
Jacob Hoffman-Andrews