tel

tel

OTLP metrics and traces for Go. The record path is allocation-sensitive; export is batched OTLP/gRPC—keep those worlds separate.

Module: github.com/gopherust-io/tel · Architecture · JetStream: nats

go get github.com/gopherust-io/tel@latest

Example

Env-first (recommended): put knobs in the process environment or a .env file. tel.Init loads .env (if present), parses config, configures the logger, and starts exporters:

package main

import (
	"context"
	"log"

	"github.com/gopherust-io/tel"
)

func main() {
	ctx := context.Background()
	t, shutdown := tel.Init(ctx) // .env + GetConfigFromEnv + ConfigureLogger + Start + SetGlobal
	defer shutdown(ctx)

	ctx = tel.WrapContext(ctx, t)
	processed, err := t.Registry().Counter("orders.processed")
	if err != nil {
		log.Fatal(err)
	}
	processed.AddWith(ctx, 1, "orders.created")
}

Local/tests without a collector: tel.InitWithConfig(ctx, tel.DefaultDebugConfig()) (skips .env).

Environment knobs

Record

Create instruments once. Use subject-keyed *With helpers—they hit AttrCache. Subjects must be a bounded set or you will blow cardinality.

r := tel.FromCtx(ctx).Registry()

count, err := r.Counter("orders.processed")
if err != nil {
	return err
}
latency, err := r.Histogram("orders.latency_seconds")
if err != nil {
	return err
}

count.AddWith(ctx, 1, "orders.created")

timer := tel.NewTimer(latency)
timer.Start()
// work
timer.StopWith(ctx, "orders.created")

Propagate

headers := tel.InjectContext(ctx, nil)
ctx = tel.ExtractContext(ctx, inboundHeaders)

Prefer MessagingSystem / MessagingSubject (and friends) over hand-rolled attribute maps.

Logging

Process-global zerolog via tel.InitLogger / tel.ConfigureLogger and tel.Info() / tel.Ctx(ctx).

LOG_ENCODE: console / text (zerolog ConsoleWriter, default) | json (compact) | pretty / json_pretty (indented JSON).

ConfigureLogger attaches resource fields when set: service, pod, namespace, environment, version.

pod comes from Config.Pod / POD_NAME, else HOSTNAME, else os.Hostname(). Set TEL_SERVICE_NAME to the app name and POD_NAME (Downward API) for the instance.

Every line includes caller as funcName:line (e.g. main.main:42). Err(err) adds a stack field (func/file/line frames) for the call path to the log site.

Trace correlation

Use context-aware helpers so log lines carry trace_id / span_id from the active span. StartSpan also stores an enriched logger on the returned context.

ctx, span := tel.FromCtx(ctx).StartSpan(ctx, "orders.create")
defer tel.EndSpan(span, err)

tel.InfoCtx(ctx).Msg("creating order")

Or wrap work with TraceFunc (span + one log line with function and duration):

err := tel.TraceFunc(ctx, "orders.create", func(ctx context.Context) error {
	return createOrder(ctx)
})

Operation metadata

start := time.Now()
// ...
tel.Duration(tel.Func(tel.InfoCtx(ctx), "HandlePay"), time.Since(start)).Msg("done")

Context fields

Immutable bag (copy-on-write). Nested WithFields appends; last key wins when logged.

ctx = tel.WithFields(ctx, tel.StrField("component", "api"), tel.IntField("user_shard", 3))
tel.InfoCtx(ctx).Msg("handling")

Log rate limits

Off by default (LOGS_MAX_MESSAGES_PER_SECOND=0). When set, ConfigureLogger installs an allocation-free RateSampler (atomics; never drops fatal/panic). Optional per-level caps: LOGS_MAX_LEVEL_MESSAGES_PER_SECOND=debug=50,info=200.

Trace sampling

TEL_TRACES_SAMPLER (default parentbased_statustraceidratio:0.1): always | never | traceidratio:N | statustraceidratio:N | parentbased_*. Status sampler force-records when start attrs/links include error (attrs at StartSpan only). DefaultDebugConfig() uses always.

fasthttp middleware

Native middleware (no net/http adaptor). Default span name is the HTTP method (low cardinality).

import telfasthttp "github.com/gopherust-io/tel/middleware/fasthttp"

h := telfasthttp.Server(next,
    telfasthttp.WithSkipPrefixes("/health", "/metrics"),
)

Knobs

Compression sets the process-wide gRPC gzip level. Default export is insecure—fine for a local collector; use TelConfig.Raw PEM for TLS/mTLS.

Lifecycle

Call Start before recording. Instruments obtained before Start are invalidated when Start runs—re-fetch via Registry() afterward. Shutdown is restart-safe (Start → Shutdown → Start → Shutdown).

Do not

1. Put network I/O, locks, or attribute allocation on the record path.
2. Pass unbounded strings (user IDs, raw URLs) as *With subjects.
3. Skip Start on a production DefaultConfig() and assume metrics still export.
4. Keep using Counter/Histogram handles created before Start.

Development

make test
make demo

CONTRIBUTING.md

License

Apache License 2.0 — see LICENSE.