tracing: Support sampling on Elastic APM (#2049)

* support sampling on Elastic APM tracing

fixes #2039

Signed-off-by: Igor Wiedler <iwiedler@gitlab.com>

* add CHANGELOG entry

Signed-off-by: Igor Wiedler <iwiedler@gitlab.com>

* set sample_rate to default value of 0 in docs

Signed-off-by: Igor Wiedler <iwiedler@gitlab.com>

CHANGELOG.md

@@ -24,6 +24,7 @@ We use *breaking* word for marking changes that are not backward compatible (rel
 - [#1939](https://github.com/thanos-io/thanos/pull/1939) Ruler: Add TLS and authentication support for query endpoints with the `--query.config` and `--query.config-file` CLI flags. See [documentation](docs/components/rule.md/#configuration) for further information.
 - [#1982](https://github.com/thanos-io/thanos/pull/1982) Ruler: Add support for Alertmanager v2 API endpoints.
 - #2030 Query: Add `thanos_proxy_store_empty_stream_responses_total` metric for number of empty responses from stores.
+- [#2049](https://github.com/thanos-io/thanos/pull/2049) Tracing: Support sampling on Elastic APM with new sample_rate setting.
 
 ### Changed
 

docs/tracing.md

@@ -100,6 +100,7 @@ config:
   service_name: ""
   service_version: ""
   service_environment: ""
+  sample_rate: 0
 ```
 
 ### Lightstep

pkg/tracing/elasticapm/elastic_apm.go

@@ -10,9 +10,10 @@ import (
 )
 
 type Config struct {
-	ServiceName        string `yaml:"service_name"`
-	ServiceVersion     string `yaml:"service_version"`
-	ServiceEnvironment string `yaml:"service_environment"`
+	ServiceName        string  `yaml:"service_name"`
+	ServiceVersion     string  `yaml:"service_version"`
+	ServiceEnvironment string  `yaml:"service_environment"`
+	SampleRate         float64 `yaml:"sample_rate"`
 }
 
 func NewTracer(conf []byte) (opentracing.Tracer, io.Closer, error) {
@@ -28,6 +29,7 @@ func NewTracer(conf []byte) (opentracing.Tracer, io.Closer, error) {
 	if err != nil {
 		return nil, nil, err
 	}
+	tracer.SetSampler(apm.NewRatioSampler(config.SampleRate))
 	return apmot.New(apmot.WithTracer(tracer)), tracerCloser{tracer}, nil
 }