prometheus: Add basic metrics for alerting

- Detect if we're falling behind while downloading
- Detect if there are any found certificates alerting

1 files changed, 71 insertions, 0 deletions

diff --git a/internal/metrics/metrics.go b/internal/metrics/metrics.go
new file mode 100644
index 0000000..113d28c
--- /dev/null
+++ b/internal/metrics/metrics.go
@@ -0,0 +1,71 @@
+package metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"rgdd.se/silentct/internal/monitor"
+	"rgdd.se/silentct/pkg/storage/index"
+)
+
+type Metrics struct {
+	logSize          *prometheus.GaugeVec
+	logIndex         *prometheus.GaugeVec
+	logTimestamp     *prometheus.GaugeVec
+	certificateAlert *prometheus.GaugeVec
+}
+
+func NewMetrics(registry *prometheus.Registry) *Metrics {
+	m := &Metrics{
+		logSize: prometheus.NewGaugeVec(
+			prometheus.GaugeOpts{
+				Name: "silentct_log_size",
+				Help: "The number of entries in the log.",
+			},
+			[]string{"id"},
+		),
+		logIndex: prometheus.NewGaugeVec(
+			prometheus.GaugeOpts{
+				Name: "silentct_log_index",
+				Help: "The next log entry to be downloaded.",
+			},
+			[]string{"id"},
+		),
+		logTimestamp: prometheus.NewGaugeVec(
+			prometheus.GaugeOpts{
+				Name: "silentct_log_timestamp",
+				Help: "The log's UNIX timestamp in ms.",
+			},
+			[]string{"id"},
+		),
+		certificateAlert: prometheus.NewGaugeVec(
+			prometheus.GaugeOpts{
+				Name: "silentct_certificate_alert",
+				Help: "The time the certificate without allowlisting was found.",
+			},
+			[]string{"stored_at"},
+		),
+	}
+
+	registry.MustRegister(m.logSize, m.logIndex, m.logTimestamp, m.certificateAlert)
+	return m
+}
+
+func (m *Metrics) LogState(state monitor.State) {
+	id := state.LogID.Base64String()
+	m.logIndex.WithLabelValues(id).Set(float64(state.NextIndex))
+	m.logSize.WithLabelValues(id).Set(float64(state.TreeSize))
+	m.logTimestamp.WithLabelValues(id).Set(float64(state.Timestamp))
+}
+
+func (m *Metrics) RemoveLogState(state monitor.State) {
+	id := state.LogID.Base64String()
+	m.logIndex.Delete(prometheus.Labels{"id": id})
+	m.logSize.Delete(prometheus.Labels{"id": id})
+	m.logTimestamp.Delete(prometheus.Labels{"id": id})
+}
+
+func (m *Metrics) CertificateAlert(alerts []index.CertificateInfo) {
+	m.certificateAlert.Reset()
+	for _, alert := range alerts {
+		m.certificateAlert.WithLabelValues(alert.StoredAt).Set(float64(alert.ObservedAt.Unix()))
+	}
+}