Add Jaeger remote sampler

.github/dependabot.yml

@@ -674,6 +674,24 @@ updates:
     schedule:
       interval: "weekly"
       day: "sunday"
+  - package-ecosystem: "gomod"
+    directory: "/samplers/jaegerremote"
+    labels:
+      - dependencies
+      - go
+      - "Skip Changelog"
+    schedule:
+      interval: "weekly"
+      day: "sunday"
+  - package-ecosystem: "gomod"
+    directory: "/samplers/jaegerremote/example"
+    labels:
+      - dependencies
+      - go
+      - "Skip Changelog"
+    schedule:
+      interval: "weekly"
+      day: "sunday"
   - package-ecosystem: "gomod"
     directory: "/tools"
     labels:

samplers/jaegerremote/Makefile

@@ -0,0 +1,11 @@
+PROTOC=docker run --rm -v${PWD}:${PWD} -w${PWD} otel/build-protobuf:latest --proto_path=${PWD}
+
+PROTO_INCLUDES=-I/usr/include/github.com/gogo/protobuf
+
+.PHONY: proto-gen
+proto-gen:
+	mkdir -p internal/proto-gen
+
+	$(PROTOC) $(PROTO_INCLUDES) \
+	    --gogo_out=$(PWD)/internal/proto-gen \
+	    ${PWD}/jaeger-idl/proto/api_v2/sampling.proto

samplers/jaegerremote/README.md

@@ -0,0 +1,38 @@
+# Jaeger Remote Sampler
+
+This package implements [Jaeger remote sampler](https://www.jaegertracing.io/docs/latest/sampling/#collector-sampling-configuration).
+
+## Example
+
+[example/](./example) shows how to host remote sampling strategies using the OpenTelemetry Collector.
+The Collector uses the Jaeger receiver to host the strategy file, note you do not need to send Jaeger to make use of the Jaeger remote sampling protocol. 
+
+Run the OpenTelemetry Collector using docker-compose:
+
+```shell
+$ docker-compose up -d
+```
+
+You can fetch the strategy file using curl:
+
+```shell
+$ curl 'localhost:5778/sampling?service=foo'
+$ curl 'localhost:5778/sampling?service=myService'
+```
+
+Run the Go program.
+This program will start with an initial sampling percentage of 50% and tries to fetch the sampling strategies from the OpenTelemetry Collector.
+It will print the entire Jaeger remote sampler structure every 10 seconds, this allows you to observe the internal sampler.
+
+```shell
+$ go run .
+```
+
+## Update generated Jaeger code
+
+Code is generated using the .proto files from [jaeger-idl](https://github.com/jaegertracing/jaeger-idl).
+In case [sampling.proto](./jaeger-idl/proto/api_v2/sampling.proto) is modified these have to be regenerated.
+
+```shell
+$ make proto-gen
+```

samplers/jaegerremote/constants.go

@@ -0,0 +1,32 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Copyright (c) 2021 The Jaeger Authors.
+// Copyright (c) 2017 Uber Technologies, Inc.
+
+package jaegerremote
+
+import (
+	"fmt"
+)
+
+const (
+	// defaultSamplingServerPort is the default port to fetch sampling config from, via http
+	defaultSamplingServerPort = 5778
+)
+
+var (
+	// defaultSamplingServerURL is the default url to fetch sampling config from, via http
+	defaultSamplingServerURL = fmt.Sprintf("http://127.0.0.1:%d/sampling", defaultSamplingServerPort)
+)

samplers/jaegerremote/doc.go

@@ -0,0 +1,16 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package jaegerremote implements the Jaeger Remote protocol.
+package jaegerremote // import "go.opentelemetry.io/contrib/samplers/jaegerremote"

samplers/jaegerremote/example/docker-compose.yaml

@@ -0,0 +1,11 @@
+version: "3"
+services:
+
+  otel-collector:
+    image: otel/opentelemetry-collector:latest
+    command: [ "--config=/etc/otel-collector.yaml" ]
+    volumes:
+      - ./otel-collector.yaml:/etc/otel-collector.yaml
+      - ./strategies.json:/etc/strategies.json
+    ports:
+      - "5778:5778"  # default jaeger remote sampling port

samplers/jaegerremote/example/go.mod

@@ -0,0 +1,13 @@
+module go.opentelemetry.io/contrib/samplers/jaegerremote/example
+
+go 1.16
+
+require (
+	github.com/davecgh/go-spew v1.1.1
+	go.opentelemetry.io/contrib/samplers/jaegerremote v0.22.0
+	go.opentelemetry.io/otel v1.1.0
+	go.opentelemetry.io/otel/exporters/stdout/stdouttrace v1.1.0
+	go.opentelemetry.io/otel/sdk v1.1.0
+)
+
+replace go.opentelemetry.io/contrib/samplers/jaegerremote => ../