tracing: fixed panic because of nil sampler (thanos-io#6066)

* fixed panic because of nil sampler

Signed-off-by: Vasiliy Rumyantsev <4119114+xBazilio@users.noreply.github.com>

* added CHANGELOG entry

Signed-off-by: Vasiliy Rumyantsev <4119114+xBazilio@users.noreply.github.com>

Signed-off-by: Vasiliy Rumyantsev <4119114+xBazilio@users.noreply.github.com>

CHANGELOG.md

@@ -10,6 +10,12 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 
 ## Unreleased
 
+## [v0.30.2](https://github.com/thanos-io/thanos/tree/release-0.30) - 28.01.2023
+
+### Fixed
+
+- [#6066](https://github.com/thanos-io/thanos/pull/6066) Tracing: fixed panic because of nil sampler
+
 ## [v0.30.1](https://github.com/thanos-io/thanos/tree/release-0.30) - 4.01.2023
 
 ### Fixed

pkg/tracing/jaeger/config_yaml.go

@@ -129,25 +129,28 @@ func getSampler(config Config) tracesdk.Sampler {
 	case "remote":
 		remoteOptions := getRemoteOptions(config)
 		sampler = jaegerremote.New(config.ServiceName, remoteOptions...)
+	// Fallback always to default (rate limiting).
 	case "ratelimiting":
+		fallthrough
+	default:
 		// The same config options are applicable to both remote and rate-limiting samplers.
 		remoteOptions := getRemoteOptions(config)
 		sampler = jaegerremote.New(config.ServiceName, remoteOptions...)
 		sampler, ok := sampler.(*rateLimitingSampler)
 		if ok {
 			sampler.Update(config.SamplerParam)
 		}
-	default:
-		var root tracesdk.Sampler
-		var parentOptions []tracesdk.ParentBasedSamplerOption
-		if config.SamplerParentConfig.LocalParentSampled {
-			parentOptions = append(parentOptions, tracesdk.WithLocalParentSampled(root))
-		}
-		if config.SamplerParentConfig.RemoteParentSampled {
-			parentOptions = append(parentOptions, tracesdk.WithRemoteParentSampled(root))
-		}
-		sampler = tracesdk.ParentBased(root, parentOptions...)
 	}
+
+	var parentOptions []tracesdk.ParentBasedSamplerOption
+	if config.SamplerParentConfig.LocalParentSampled {
+		parentOptions = append(parentOptions, tracesdk.WithLocalParentSampled(sampler))
+	}
+	if config.SamplerParentConfig.RemoteParentSampled {
+		parentOptions = append(parentOptions, tracesdk.WithRemoteParentSampled(sampler))
+	}
+	sampler = tracesdk.ParentBased(sampler, parentOptions...)
+
 	return sampler
 }