[cmd/opampsupervisor]: Configurable Supervisor OpAmp server port (#36002)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
Allows the Supervisor's OpAmp server port to be configurable. This is
useful for restricted environments deploying the supervisor.

<!-- Issue number (e.g. #1234) or full URL to issue, if applicable. -->
#### Link to tracking issue
Fixes #36001 

<!--Describe what testing was performed and which tests were added.-->
#### Testing
Updated tests and added an e2e test

<!--Describe the documentation added.-->
#### Documentation
Spec was updated accordingly. Also added documentation for previously
added `health_check_port` that wasn't present in spec.

<!--Please delete paragraphs that you did not use before submitting.-->

Author: dpaasman00

.chloggen/dakotapaasman_bpop-1087-supervisor-configurable-opamp-server-port.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: opampsupervisor
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Makes the Supervisor's OpAmp server port configurable with 'agent::opamp_server_port'.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [36001]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

cmd/opampsupervisor/e2e_test.go

@@ -1443,6 +1443,71 @@ func TestSupervisorLogging(t *testing.T) {
 	require.NoError(t, logFile.Close())
 }
 
+func TestSupervisorOpAmpServerPort(t *testing.T) {
+	var agentConfig atomic.Value
+	server := newOpAMPServer(
+		t,
+		defaultConnectingHandler,
+		server.ConnectionCallbacksStruct{
+			OnMessageFunc: func(_ context.Context, _ types.Connection, message *protobufs.AgentToServer) *protobufs.ServerToAgent {
+				if message.EffectiveConfig != nil {
+					config := message.EffectiveConfig.ConfigMap.ConfigMap[""]
+					if config != nil {
+						agentConfig.Store(string(config.Body))
+					}
+				}
+
+				return &protobufs.ServerToAgent{}
+			},
+		})
+
+	supervisorOpAmpServerPort, err := findRandomPort()
+	require.NoError(t, err)
+
+	s := newSupervisor(t, "server_port", map[string]string{"url": server.addr, "supervisor_opamp_server_port": fmt.Sprintf("%d", supervisorOpAmpServerPort)})
+
+	require.Nil(t, s.Start())
+	defer s.Shutdown()
+
+	waitForSupervisorConnection(server.supervisorConnected, true)
+
+	cfg, hash, inputFile, outputFile := createSimplePipelineCollectorConf(t)
+
+	server.sendToSupervisor(&protobufs.ServerToAgent{
+		RemoteConfig: &protobufs.AgentRemoteConfig{
+			Config: &protobufs.AgentConfigMap{
+				ConfigMap: map[string]*protobufs.AgentConfigFile{
+					"": {Body: cfg.Bytes()},
+				},
+			},
+			ConfigHash: hash,
+		},
+	})
+
+	require.Eventually(t, func() bool {
+		cfg, ok := agentConfig.Load().(string)
+		if ok {
+			// The effective config may be structurally different compared to what was sent,
+			// and will also have some data redacted,
+			// so just check that it includes the filelog receiver
+			return strings.Contains(cfg, "filelog")
+		}
+
+		return false
+	}, 5*time.Second, 500*time.Millisecond, "Collector was not started with remote config")
+
+	n, err := inputFile.WriteString("{\"body\":\"hello, world\"}\n")
+	require.NotZero(t, n, "Could not write to input file")
+	require.NoError(t, err)
+
+	require.Eventually(t, func() bool {
+		logRecord := make([]byte, 1024)
+		n, _ := outputFile.Read(logRecord)
+
+		return n != 0
+	}, 10*time.Second, 500*time.Millisecond, "Log never appeared in output")
+}
+
 func findRandomPort() (int, error) {
 	l, err := net.Listen("tcp", "localhost:0")
 

cmd/opampsupervisor/specification/README.md

@@ -160,7 +160,14 @@ agent:
       client.id: "01HWWSK84BMT7J45663MBJMTPJ"
     non_identifying_attributes:
       custom.attribute: "custom-value"
-      
+
+  # The port the Collector's health check extension will be configured to use
+  health_check_port:
+
+  # The port the Supervisor will start its OpAmp server on and the Collector's 
+  # OpAmp extension will connect to
+  opamp_server_port: 
+
 ```
 
 ### Operation When OpAMP Server is Unavailable

cmd/opampsupervisor/supervisor/config/config.go

@@ -155,6 +155,7 @@ type Agent struct {
 	Description             AgentDescription `mapstructure:"description"`
 	BootstrapTimeout        time.Duration    `mapstructure:"bootstrap_timeout"`
 	HealthCheckPort         int              `mapstructure:"health_check_port"`
+	OpAMPServerPort         int              `mapstructure:"opamp_server_port"`
 	PassthroughLogs         bool             `mapstructure:"passthrough_logs"`
 }
 
@@ -171,6 +172,10 @@ func (a Agent) Validate() error {
 		return errors.New("agent::health_check_port must be a valid port number")
 	}
 
+	if a.OpAMPServerPort < 0 || a.OpAMPServerPort > 65535 {
+		return errors.New("agent::opamp_server_port must be a valid port number")
+	}
+
 	if a.Executable == "" {
 		return errors.New("agent::executable must be specified")
 	}

cmd/opampsupervisor/supervisor/config/config_test.go

@@ -227,7 +227,7 @@ func TestValidate(t *testing.T) {
 			expectedError: "agent::orphan_detection_interval must be positive",
 		},
 		{
-			name: "Invalid port number",
+			name: "Invalid health check port number",
 			config: Supervisor{
 				Server: OpAMPServer{
 					Endpoint: "wss://localhost:9090/opamp",
@@ -254,7 +254,7 @@ func TestValidate(t *testing.T) {
 			expectedError: "agent::health_check_port must be a valid port number",
 		},
 		{
-			name: "Zero value port number",
+			name: "Zero value health check port number",
 			config: Supervisor{
 				Server: OpAMPServer{
 					Endpoint: "wss://localhost:9090/opamp",
@@ -280,7 +280,7 @@ func TestValidate(t *testing.T) {
 			},
 		},
 		{
-			name: "Normal port number",
+			name: "Normal health check port number",
 			config: Supervisor{
 				Server: OpAMPServer{
 					Endpoint: "wss://localhost:9090/opamp",
@@ -331,6 +331,53 @@ func TestValidate(t *testing.T) {
 			},
 			expectedError: "agent::bootstrap_timeout must be positive",
 		},
+		{
+			name: "Invalid opamp server port number",
+			config: Supervisor{
+				Server: OpAMPServer{
+					Endpoint: "wss://localhost:9090/opamp",
+					Headers: http.Header{
+						"Header1": []string{"HeaderValue"},
+					},
+				},
+				Agent: Agent{
+					Executable:              "${file_path}",
+					OrphanDetectionInterval: 5 * time.Second,
+					OpAMPServerPort:         65536,
+					BootstrapTimeout:        5 * time.Second,
+				},
+				Capabilities: Capabilities{
+					AcceptsRemoteConfig: true,
+				},
+				Storage: Storage{
+					Directory: "/etc/opamp-supervisor/storage",
+				},
+			},
+			expectedError: "agent::opamp_server_port must be a valid port number",
+		},
+		{
+			name: "Zero value opamp server port number",
+			config: Supervisor{
+				Server: OpAMPServer{
+					Endpoint: "wss://localhost:9090/opamp",
+					Headers: http.Header{
+						"Header1": []string{"HeaderValue"},
+					},
+				},
+				Agent: Agent{
+					Executable:              "${file_path}",
+					OrphanDetectionInterval: 5 * time.Second,
+					OpAMPServerPort:         0,
+					BootstrapTimeout:        5 * time.Second,
+				},
+				Capabilities: Capabilities{
+					AcceptsRemoteConfig: true,
+				},
+				Storage: Storage{
+					Directory: "/etc/opamp-supervisor/storage",
+				},
+			},
+		},
 	}
 
 	// create some fake files for validating agent config

cmd/opampsupervisor/supervisor/supervisor.go

@@ -263,7 +263,7 @@ func (s *Supervisor) createTemplates() error {
 // shuts down the Collector. This only needs to happen
 // once per Collector binary.
 func (s *Supervisor) getBootstrapInfo() (err error) {
-	s.opampServerPort, err = s.findRandomPort()
+	s.opampServerPort, err = s.getSupervisorOpAMPServerPort()
 	if err != nil {
 		return err
 	}
@@ -457,7 +457,7 @@ func (s *Supervisor) startOpAMPServer() error {
 	s.opampServer = server.New(newLoggerFromZap(s.logger))
 
 	var err error
-	s.opampServerPort, err = s.findRandomPort()
+	s.opampServerPort, err = s.getSupervisorOpAMPServerPort()
 	if err != nil {
 		return err
 	}
@@ -1345,6 +1345,13 @@ func (s *Supervisor) agentConfigFilePath() string {
 	return filepath.Join(s.config.Storage.Directory, agentConfigFileName)
 }
 
+func (s *Supervisor) getSupervisorOpAMPServerPort() (int, error) {
+	if s.config.Agent.OpAMPServerPort != 0 {
+		return s.config.Agent.OpAMPServerPort, nil
+	}
+	return s.findRandomPort()
+}
+
 func (s *Supervisor) findRandomPort() (int, error) {
 	l, err := net.Listen("tcp", "localhost:0")
 

cmd/opampsupervisor/testdata/supervisor/supervisor_server_port.yaml

@@ -0,0 +1,17 @@
+server:
+  endpoint: ws://{{.url}}/v1/opamp
+
+capabilities:
+  reports_effective_config: true
+  reports_own_metrics: true
+  reports_health: true
+  accepts_remote_config: true
+  reports_remote_config: true
+  accepts_restart_command: true
+
+storage:
+  directory: '{{.storage_dir}}'
+
+agent:
+  executable: ../../bin/otelcontribcol_{{.goos}}_{{.goarch}}{{.extension}}
+  opamp_server_port: {{ .supervisor_opamp_server_port }}