f-21: mon: add prometheus data

Signed-off-by: GnomeZworc <nicolas.boufidjeline@g3e.fr>

internal/prometheus/agent/collector.go

@@ -0,0 +1,67 @@
+package agentmetrics
+
+import (
+	"strings"
+
+	"git.g3e.fr/syonad/two/pkg/db/kv"
+	"github.com/dgraph-io/badger/v4"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var allStates = []string{"creating", "created", "deleting", "deleted"}
+
+// AgentCollector implements prometheus.Collector and exposes agent metrics
+// by querying the BadgerDB on each scrape.
+type AgentCollector struct {
+	db           *badger.DB
+	vpcsTotal    *prometheus.Desc
+	subnetsTotal *prometheus.Desc
+}
+
+func NewAgentCollector(db *badger.DB) *AgentCollector {
+	return &AgentCollector{
+		db: db,
+		vpcsTotal: prometheus.NewDesc(
+			"syonad_vpcs_total",
+			"Number of VPCs by state.",
+			[]string{"state"}, nil,
+		),
+		subnetsTotal: prometheus.NewDesc(
+			"syonad_subnets_total",
+			"Number of subnets by state.",
+			[]string{"state"}, nil,
+		),
+	}
+}
+
+func (c *AgentCollector) Describe(ch chan<- *prometheus.Desc) {
+	ch <- c.vpcsTotal
+	ch <- c.subnetsTotal
+}
+
+func (c *AgentCollector) Collect(ch chan<- prometheus.Metric) {
+	c.collectStates(ch, "vpc/", c.vpcsTotal)
+	c.collectStates(ch, "subnet/", c.subnetsTotal)
+}
+
+// collectStates counts resources under the given DB prefix by their state value
+// and emits one gauge per state label.
+func (c *AgentCollector) collectStates(ch chan<- prometheus.Metric, prefix string, desc *prometheus.Desc) {
+	counts := make(map[string]float64, len(allStates))
+	for _, s := range allStates {
+		counts[s] = 0
+	}
+
+	items, err := kv.ListByPrefix(c.db, prefix)
+	if err == nil {
+		for key, val := range items {
+			if strings.HasSuffix(key, "/state") {
+				counts[val]++
+			}
+		}
+	}
+
+	for _, state := range allStates {
+		ch <- prometheus.MustNewConstMetric(desc, prometheus.GaugeValue, counts[state], state)
+	}
+}

pkg/prometheus/server.go

@@ -0,0 +1,20 @@
+package promserver
+
+import (
+	"log"
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+// Start launches the Prometheus metrics HTTP server on the given address.
+// The provided registry is used to expose metrics at /metrics.
+func Start(address string, registry *prometheus.Registry) {
+	mux := http.NewServeMux()
+	mux.Handle("/metrics", promhttp.HandlerFor(registry, promhttp.HandlerOpts{
+		EnableOpenMetrics: true,
+	}))
+	log.Printf("Prometheus server listening on %s", address)
+	log.Fatal(http.ListenAndServe(address, mux))
+}