Move source-tag to toplevel maglev.source-tag config, defaulting to short hostname, v1.1.2

Makefile

@@ -15,7 +15,7 @@ FRONTEND_WEB_SRC := $(shell find cmd/frontend/web/src -type f 2>/dev/null) \
 FRONTEND_WEB_DIST := cmd/frontend/web/dist/index.html
 
 NATIVE_ARCH  := $(shell go env GOARCH)
-VERSION      := 1.1.0
+VERSION      := 1.1.2
 COMMIT_HASH  := $(shell git rev-parse --short HEAD 2>/dev/null || echo unknown)
 DATE         := $(shell date -u +%Y-%m-%dT%H:%M:%SZ)
 LDFLAGS      := -X '$(MODULE)/cmd.version=$(VERSION)' \

cmd/server/main.go

@@ -150,7 +150,7 @@ func run() error {
 		if vppClient != nil {
 			vppSrc = vppClient
 		}
-		metrics.Register(reg, chkr, vppSrc)
+		metrics.Register(reg, chkr, vppSrc, cfg.SourceTag)
 		reg.MustRegister(grpcMetrics)
 
 		mux := http.NewServeMux()

internal/config/config.go

@@ -17,6 +17,7 @@ import (
 
 // Config is the top-level parsed and validated configuration.
 type Config struct {
+	SourceTag     string // this node's nginx source tag; defaults to the short hostname
 	HealthChecker HealthCheckerConfig
 	VPP           VPPConfig
 	HealthChecks  map[string]HealthCheck
@@ -163,6 +164,7 @@ type rawConfig struct {
 }
 
 type rawMaglev struct {
+	SourceTag     string                    `yaml:"source-tag"`
 	HealthChecker rawHealthCheckerCfg       `yaml:"healthchecker"`
 	VPP           rawVPPCfg                 `yaml:"vpp"`
 	HealthChecks  map[string]rawHealthCheck `yaml:"healthchecks"`
@@ -299,6 +301,18 @@ func parse(data []byte) (*Config, error) {
 func convert(r *rawMaglev) (*Config, error) {
 	cfg := &Config{}
 
+	// ---- source-tag -----------------------------------------------------------
+	cfg.SourceTag = r.SourceTag
+	if cfg.SourceTag == "" {
+		if h, err := os.Hostname(); err == nil {
+			if dot := strings.IndexByte(h, '.'); dot > 0 {
+				cfg.SourceTag = h[:dot]
+			} else {
+				cfg.SourceTag = h
+			}
+		}
+	}
+
 	// ---- healthchecker --------------------------------------------------------
 	cfg.HealthChecker.Netns = r.HealthChecker.Netns
 	cfg.HealthChecker.TransitionHistory = r.HealthChecker.TransitionHistory

internal/metrics/metrics.go

@@ -131,9 +131,11 @@ var (
 // on each scrape. This avoids stale label sets when backends are added or
 // removed by a config reload.
 type Collector struct {
-	src StateSource
-	vpp VPPSource // optional; nil when VPP integration is disabled
+	src       StateSource
+	vpp       VPPSource // optional; nil when VPP integration is disabled
+	sourceTag string
 
+	maglevInfo     *prometheus.Desc
 	backendState   *prometheus.Desc
 	backendHealth  *prometheus.Desc
 	backendEnabled *prometheus.Desc
@@ -152,10 +154,16 @@ type Collector struct {
 // NewCollector creates a Collector backed by the given StateSource. vpp may
 // be nil when VPP integration is disabled; in that case vpp_* metrics are
 // simply not emitted.
-func NewCollector(src StateSource, vpp VPPSource) *Collector {
+func NewCollector(src StateSource, vpp VPPSource, sourceTag string) *Collector {
 	return &Collector{
-		src: src,
-		vpp: vpp,
+		src:       src,
+		vpp:       vpp,
+		sourceTag: sourceTag,
+		maglevInfo: prometheus.NewDesc(
+			"maglev_info",
+			"Static maglevd instance metadata. Always 1; metadata is conveyed via labels.",
+			[]string{"source_tag"}, nil,
+		),
 		backendState: prometheus.NewDesc(
 			"maglev_backend_state",
 			"Current backend state (1 = active for the given state label).",
@@ -216,6 +224,7 @@ func NewCollector(src StateSource, vpp VPPSource) *Collector {
 
 // Describe implements prometheus.Collector.
 func (c *Collector) Describe(ch chan<- *prometheus.Desc) {
+	ch <- c.maglevInfo
 	ch <- c.backendState
 	ch <- c.backendHealth
 	ch <- c.backendEnabled
@@ -231,6 +240,8 @@ func (c *Collector) Describe(ch chan<- *prometheus.Desc) {
 
 // Collect implements prometheus.Collector.
 func (c *Collector) Collect(ch chan<- prometheus.Metric) {
+	ch <- prometheus.MustNewConstMetric(c.maglevInfo, prometheus.GaugeValue, 1.0, c.sourceTag)
+
 	states := []health.State{
 		health.StateUnknown,
 		health.StateUp,
@@ -343,8 +354,8 @@ func (c *Collector) Collect(ch chan<- prometheus.Metric) {
 
 // Register registers all metrics with the given registry. vpp may be nil
 // to disable VPP-related metrics.
-func Register(reg prometheus.Registerer, src StateSource, vpp VPPSource) *Collector {
-	coll := NewCollector(src, vpp)
+func Register(reg prometheus.Registerer, src StateSource, vpp VPPSource, sourceTag string) *Collector {
+	coll := NewCollector(src, vpp, sourceTag)
 	reg.MustRegister(coll)
 	reg.MustRegister(ProbeTotal)
 	reg.MustRegister(ProbeDuration)