metrics.go

// Copyright © 2021 Attestant Limited.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package main

import (
	"context"

	"github.com/attestantio/dirk/services/metrics"
	"github.com/pkg/errors"
	"github.com/prometheus/client_golang/prometheus"
)

var metricsNamespace = "dirk"

var (
	releaseMetric *prometheus.GaugeVec
	readyMetric   prometheus.Gauge
)

func registerMetrics(ctx context.Context, monitor metrics.Service) error {
	if releaseMetric != nil {
		// Already registered.
		return nil
	}
	if monitor == nil {
		// No monitor.
		return nil
	}
	switch monitor.Presenter() {
	case "prometheus":
		return registerPrometheusMetrics(ctx)
	case "null":
		log.Debug().Msg("no metrics will be generated for this module")
	}
	return nil
}

func registerPrometheusMetrics(_ context.Context) error {
	startTime := prometheus.NewGauge(prometheus.GaugeOpts{
		Namespace: metricsNamespace,
		Name:      "start_time_secs",
		Help:      "The timestamp at which this instance started.",
	})
	if err := prometheus.Register(startTime); err != nil {
		return errors.Wrap(err, "failed to regsiter start_time_secs")
	}
	startTime.SetToCurrentTime()

	releaseMetric = prometheus.NewGaugeVec(prometheus.GaugeOpts{
		Namespace: metricsNamespace,
		Name:      "release",
		Help:      "The release of this instance.",
	}, []string{"version"})
	if err := prometheus.Register(releaseMetric); err != nil {
		return err
	}

	readyMetric = prometheus.NewGauge(prometheus.GaugeOpts{
		Namespace: metricsNamespace,
		Name:      "ready",
		Help:      "1 if ready to serve requests, otherwise 0.",
	})
	if err := prometheus.Register(readyMetric); err != nil {
		return errors.Wrap(err, "failed to regsiter ready")
	}

	return nil
}

// SetRelease is called when the release version is established.
func setRelease(_ context.Context, version string) {
	if releaseMetric == nil {
		return
	}

	releaseMetric.WithLabelValues(version).Set(1)
}

func setReady(_ context.Context, ready bool) {
	if readyMetric == nil {
		return
	}

	if ready {
		readyMetric.Set(1)
	} else {
		readyMetric.Set(0)
	}
}