Ilia Denisov
111 lines
3.4 KiB
Go
111 lines
3.4 KiB
Go
// Package metrics emits per-request OpenTelemetry counters and histograms
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// scoped by route group.
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//
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// The metric names are fixed by `backend/README.md` §15:
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//
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// - http_requests_total{group, method, route, status}
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// - http_request_duration_seconds{group, method, route, status}
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//
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// One Middleware instance per route group keeps the `group` attribute stable
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// across requests while allowing the gin router to share the same Meter.
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package metrics
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import (
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"strconv"
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"time"
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"github.com/gin-gonic/gin"
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"go.opentelemetry.io/otel/attribute"
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"go.opentelemetry.io/otel/metric"
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)
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// Group identifies the route family that emits the metric. The set is closed
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// and matches the prefixes registered by router.New.
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type Group string
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const (
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// GroupRoot covers `/healthz`, `/readyz`, and unmatched routes.
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GroupRoot Group = "root"
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// GroupProbes covers the readiness/liveness probes when reported separately
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// from other root-level traffic.
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GroupProbes Group = "probes"
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// GroupPublic covers `/api/v1/public/*` endpoints.
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GroupPublic Group = "public"
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// GroupUser covers `/api/v1/user/*` endpoints.
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GroupUser Group = "user"
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// GroupAdmin covers `/api/v1/admin/*` endpoints.
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GroupAdmin Group = "admin"
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// GroupInternal covers `/api/v1/internal/*` endpoints.
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GroupInternal Group = "internal"
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)
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// Instruments holds the shared metric instruments used by every Group-scoped
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// middleware. The instruments are constructed once per Meter; the
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// per-middleware closure binds them to the right `group` attribute.
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type Instruments struct {
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requestsTotal metric.Int64Counter
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requestDuration metric.Float64Histogram
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}
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// NewInstruments builds the shared metric instruments from meter. A nil meter
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// returns nil instruments and disables metric emission.
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func NewInstruments(meter metric.Meter) (*Instruments, error) {
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if meter == nil {
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return nil, nil
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}
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requestsTotal, err := meter.Int64Counter(
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"http_requests_total",
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metric.WithDescription("Number of HTTP requests served by the backend, partitioned by route group, method, route, and response status."),
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metric.WithUnit("1"),
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)
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if err != nil {
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return nil, err
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}
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requestDuration, err := meter.Float64Histogram(
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"http_request_duration_seconds",
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metric.WithDescription("Duration of HTTP requests served by the backend, partitioned by route group, method, route, and response status."),
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metric.WithUnit("s"),
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)
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if err != nil {
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return nil, err
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}
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return &Instruments{
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requestsTotal: requestsTotal,
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requestDuration: requestDuration,
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}, nil
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}
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// Middleware returns a gin middleware that records request counters and
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// duration histograms with the `group` attribute fixed to group. A nil
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// instruments value yields a no-op middleware so that metric emission is
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// strictly opt-in.
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func Middleware(instruments *Instruments, group Group) gin.HandlerFunc {
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if instruments == nil {
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return func(c *gin.Context) { c.Next() }
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}
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return func(c *gin.Context) {
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start := time.Now()
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c.Next()
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duration := time.Since(start)
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route := c.FullPath()
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if route == "" {
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route = "unmatched"
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}
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attrs := metric.WithAttributes(
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attribute.String("group", string(group)),
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attribute.String("method", c.Request.Method),
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attribute.String("route", route),
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attribute.String("status", strconv.Itoa(c.Writer.Status())),
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)
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instruments.requestsTotal.Add(c.Request.Context(), 1, attrs)
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instruments.requestDuration.Record(c.Request.Context(), duration.Seconds(), attrs)
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}
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}
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