metrics: add initial job metrics

Add job metrics to track the number of
pending/running jobs, the duration of
the jobs and how long the jobs spent in
the job queue.

internal/prometheus/job_metrics.go

@@ -0,0 +1,46 @@
+package prometheus
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+const workerSubsystem = "composer_worker"
+
+var (
+	PendingJobs = promauto.NewGaugeVec(prometheus.GaugeOpts{
+		Name:      "pending_jobs",
+		Namespace: namespace,
+		Subsystem: workerSubsystem,
+		Help:      "Currently pending jobs",
+	}, []string{"type"})
+)
+
+var (
+	RunningJobs = promauto.NewGaugeVec(prometheus.GaugeOpts{
+		Name:      "running_jobs",
+		Namespace: namespace,
+		Subsystem: workerSubsystem,
+		Help:      "Currently running jobs",
+	}, []string{"type"})
+)
+
+var (
+	JobDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Name:      "job_duration_seconds",
+		Namespace: namespace,
+		Subsystem: workerSubsystem,
+		Help:      "Duration spent by workers on a job.",
+		Buckets:   []float64{.1, .2, .5, 1, 2, 4, 8, 16, 32, 64, 96, 128, 160, 192, 224, 256, 320, 382, 448, 512, 640, 768, 896, 1024, 1280, 1536, 1792, 2049},
+	}, []string{"type"})
+)
+
+var (
+	JobWaitDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Name:      "job_wait_duration_seconds",
+		Namespace: namespace,
+		Subsystem: workerSubsystem,
+		Help:      "Duration a job spends on the queue.",
+		Buckets:   []float64{.1, .2, .5, 1, 2, 4, 8, 16, 32, 64, 96, 128, 160, 192, 224, 256, 320, 382, 448, 512, 640, 768, 896, 1024, 1280, 1536, 1792, 2049},
+	}, []string{"type"})
+)