[OpAMP] Introduce /v1/opamp endpoint behind feature flag

docs/opamp.md

@@ -0,0 +1,63 @@
+# OpAMP
+
+This section describes how to connect a OpenTelemetry Collector instance to Fleet Server over OpAMP.
+
+1. Create a deployment in Elastic Cloud.  Integrations Server is not needed as we will instead be
+   using the Fleet Server instance built from this repository so it can "speak" OpAMP to the OpenTelemetry
+   Collector.
+2. Create an Elasticsearch service account token using Kibana > Dev Tools > Console.
+   ```
+   POST /_security/service/elastic/fleet-server/credential/token/opamp
+   ```
+3. Enable the OpAMP feature flag in the `fleet-server.yml` file by adding the following snippet to the `fleet-server` input
+   section, as a sibling of the `policy.id` key:
+   ```yml
+   server:
+     feature_flags:
+       enable_opamp: true
+   ```
+
+4. Build the Fleet Server binary for your platform.
+   ```
+   mage build:local
+   ```
+5. Run the Fleet Server binary with the above configuration.
+   ```
+   ./bin/fleet-server
+   ```
+6. Create a new policy in Fleet. Copy the enrollment token for that policy.
+7. Create OpenTelemetry Collector configuration for connecting to the Fleet Server instance and save it as `otel-opamp.yaml`.
+   ```yaml
+   receivers:
+     otlp:
+       protocols:
+         grpc:
+           endpoint: 0.0.0.0:4317
+
+   exporters:
+     debug:
+       verbosity: detailed
+
+   extensions:
+     opamp:
+       server:
+         http:
+           endpoint: http://localhost:8220/v1/opamp
+           tls:
+             insecure: true
+           headers:
+             Authorization: ApiKey ${env:FLEET_ENROLLMENT_TOKEN}
+       instance_uid: "019b8d7a-2da8-7657-b52d-492a9de33319"
+
+   service:
+     pipelines:
+       logs:
+         receivers: [otlp]
+         exporters: [debug]
+         extensions: [opamp]
+   ```
+7. Download and extract an OpenTelemetry Collector Contrib release for your platform from https://github.com/open-telemetry/opentelemetry-collector-releases/releases
+8. Run the OpenTelemetry Collector with the above configuration.
+   ```
+   API_KEY=<enrollment token> ./otelcol-contrib --config ./otel-opamp.yaml
+   ```

fleet-server.reference.yml

@@ -277,6 +277,9 @@ fleet:
 #        // POLICY_CHANGE actions need an explicit ack if this is set.
 #        ignore_checkin_policy_id: false
 #
+#        // enable OpAMP endpoint
+#        enable_opamp: false
+#
 #    # monitor options are advanced configuration and should not be adjusted is most cases
 #    monitor:
 #      fetch_size: 1000 # The number of documents that each monitor may fetch at once

go.mod

@@ -23,6 +23,7 @@ require (
 	github.com/mailru/easyjson v0.9.1
 	github.com/miolini/datacounter v1.0.3
 	github.com/oapi-codegen/runtime v1.1.2
+	github.com/open-telemetry/opamp-go v0.22.0
 	github.com/pbnjay/memory v0.0.0-20210728143218-7b4eea64cf58
 	github.com/prometheus/client_golang v1.23.2
 	github.com/rs/xid v1.6.0
@@ -36,6 +37,7 @@ require (
 	go.elastic.co/apm/module/apmzerolog/v2 v2.7.3
 	go.elastic.co/apm/v2 v2.7.3
 	go.elastic.co/ecszerolog v0.2.0
+	go.opentelemetry.io/otel v1.39.0
 	go.uber.org/zap v1.27.1
 	golang.org/x/net v0.50.0
 	golang.org/x/sync v0.19.0
@@ -63,6 +65,7 @@ require (
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-ole/go-ole v1.3.0 // indirect
 	github.com/google/uuid v1.6.0 // indirect
+	github.com/gorilla/websocket v1.5.3 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/josharian/intern v1.0.0 // indirect
 	github.com/lufia/plan9stats v0.0.0-20211012122336-39d0f177ccd0 // indirect
@@ -87,7 +90,6 @@ require (
 	go.elastic.co/ecszap v1.0.3 // indirect
 	go.elastic.co/fastjson v1.5.1 // indirect
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
-	go.opentelemetry.io/otel v1.39.0 // indirect
 	go.opentelemetry.io/otel/metric v1.39.0 // indirect
 	go.opentelemetry.io/otel/trace v1.39.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect

go.sum

@@ -83,6 +83,8 @@ github.com/google/pprof v0.0.0-20230426061923-93006964c1fc h1:AGDHt781oIcL4EFk7c
 github.com/google/pprof v0.0.0-20230426061923-93006964c1fc/go.mod h1:79YE0hCXdHag9sBkw2o+N/YnZtTkXi0UT9Nnixa5eYk=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/gorilla/websocket v1.5.3 h1:saDtZ6Pbx/0u+bgYQ3q96pZgCzfhKXGPqt7kZ72aNNg=
+github.com/gorilla/websocket v1.5.3/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
 github.com/hashicorp/go-cleanhttp v0.5.2 h1:035FKYIWjmULyFRBKPs8TBQoi0x6d9G4xc9neXJWAZQ=
 github.com/hashicorp/go-cleanhttp v0.5.2/go.mod h1:kO/YDlP8L1346E6Sodw+PrpBSV4/SoxCXGY6BqNFT48=
 github.com/hashicorp/go-version v1.8.0 h1:KAkNb1HAiZd1ukkxDFGmokVZe1Xy9HG6NUp+bPle2i4=
@@ -123,6 +125,8 @@ github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
 github.com/oapi-codegen/runtime v1.1.2 h1:P2+CubHq8fO4Q6fV1tqDBZHCwpVpvPg7oKiYzQgXIyI=
 github.com/oapi-codegen/runtime v1.1.2/go.mod h1:SK9X900oXmPWilYR5/WKPzt3Kqxn/uS/+lbpREv+eCg=
+github.com/open-telemetry/opamp-go v0.22.0 h1:7UnsQgFFS7ffM09JQk+9aGVBAAlsLfcooZ9xvSYwxWM=
+github.com/open-telemetry/opamp-go v0.22.0/go.mod h1:339N71soCPrhHywbAcKUZJDODod581ZOxCpTkrl3zYQ=
 github.com/opencontainers/go-digest v1.0.0 h1:apOUWs51W5PlhuyGyz9FCeeBIOUDA/6nW8Oi/yOhh5U=
 github.com/opencontainers/go-digest v1.0.0/go.mod h1:0JzlMkj0TRzQZfJkVvzbP0HBR3IKzErnv2BNG4W4MAM=
 github.com/opencontainers/image-spec v1.0.2 h1:9yCKha/T5XdGtO0q9Q9a6T5NUCsTn/DrBg0D7ufOcFM=

internal/pkg/api/api.go

@@ -46,6 +46,12 @@ func WithStatus(st *StatusT) APIOpt {
 	}
 }
 
+func WithOpAMP(oa *OpAMPT) APIOpt {
+	return func(a *apiServer) {
+		a.oa = oa
+	}
+}
+
 func WithUpload(ut *UploadT) APIOpt {
 	return func(a *apiServer) {
 		a.ut = ut
@@ -84,6 +90,7 @@ type apiServer struct {
 	at    *ArtifactT
 	ack   *AckT
 	st    *StatusT
+	oa    *OpAMPT
 	ut    *UploadT
 	ft    *FileDeliveryT
 	pt    *PGPRetrieverT