Add optional OpenTelemetry Netty server instrumentation

- Update lys.version to 2026.04.14

- Add optional compileOnly dependency on opentelemetry-netty-4.1 in rbcs-server

- Add runtime guard to only activate instrumentation when OTel classes are on classpath

- Insert OTel combined handler after HttpServerCodec in the Netty pipeline

- Add requires-static JPMS directives for optional module support

gradle.properties

@@ -4,7 +4,7 @@ org.gradle.caching=true
 
 rbcs.version = 0.5.0
 
-lys.version = 2026.03.26
+lys.version = 2026.04.28
 
 gitea.maven.url = https://gitea.woggioni.net/api/packages/woggioni/maven
 docker.registry.url=gitea.woggioni.net

rbcs-api/src/main/java/net/woggioni/rbcs/api/Configuration.java

@@ -16,6 +16,7 @@ import java.util.stream.Collectors;
 
 @Value
 public class Configuration {
+    boolean enableTelemetry;
     String host;
     int port;
     boolean proxyProtocolEnabled;
@@ -150,6 +151,7 @@ public class Configuration {
     }
 
     public static Configuration of(
+            boolean enableTelemetry,
             String host,
             int port,
             boolean proxyProtocolEnabled,
@@ -166,6 +168,7 @@ public class Configuration {
             Tls tls
     ) {
         return new Configuration(
+                enableTelemetry,
                 host,
                 port,
                 proxyProtocolEnabled,

rbcs-server/build.gradle

@@ -13,6 +13,11 @@ dependencies {
     implementation catalog.netty.buffer
     implementation catalog.netty.transport
     implementation catalog.netty.codec.haproxy
+    compileOnly catalog.opentelemetry.netty['4']['1']
+    compileOnly catalog.opentelemetry.sdk.extension.autoconfigure
+    compileOnly catalog.opentelemetry.logback.appender['1']['0']
+    compileOnly catalog.opentelemetry.extension.trace.propagators
+    compileOnly catalog.logback.classic
 
     api project(':rbcs-common')
     api project(':rbcs-api')

rbcs-server/src/main/java/module-info.java

@@ -17,6 +17,11 @@ module net.woggioni.rbcs.server {
     requires io.netty.common;
     requires io.netty.codec;
     requires io.netty.codec.haproxy;
+    requires static io.opentelemetry.api;
+    requires static io.opentelemetry.instrumentation.netty_4_1;
+    requires static io.opentelemetry.sdk.autoconfigure;
+    requires static io.opentelemetry.instrumentation.logback_appender_1_0;
+    requires static io.opentelemetry.extension.trace.propagation;
     requires org.slf4j;
 
     exports net.woggioni.rbcs.server;

rbcs-server/src/main/kotlin/net/woggioni/rbcs/server/RemoteBuildCacheServer.kt

@@ -68,6 +68,8 @@ import net.woggioni.rbcs.common.Xml
 import net.woggioni.rbcs.common.createLogger
 import net.woggioni.rbcs.common.debug
 import net.woggioni.rbcs.common.info
+import net.woggioni.rbcs.server.otel.OtelIntegration
+import net.woggioni.rbcs.server.otel.OtelSdkIntegration
 import net.woggioni.rbcs.server.auth.AbstractNettyHttpAuthenticator
 import net.woggioni.rbcs.server.auth.Authorizer
 import net.woggioni.rbcs.server.auth.RoleAuthorizer
@@ -431,6 +433,7 @@ class RemoteBuildCacheServer(private val cfg: Configuration) {
                 maxChunkSize = cfg.connection.chunkSize
             }
             pipeline.addLast(HttpServerCodec(httpDecoderConfig))
+            OtelIntegration.createHandler(cfg.isEnableTelemetry)?.let { pipeline.addLast(it) }
             pipeline.addLast(ReadTriggerDuplexHandler.NAME, ReadTriggerDuplexHandler())
             pipeline.addLast(MaxRequestSizeHandler.NAME, MaxRequestSizeHandler(cfg.connection.maxRequestSize))
             pipeline.addLast(HttpChunkContentCompressor(1024))
@@ -525,6 +528,7 @@ class RemoteBuildCacheServer(private val cfg: Configuration) {
     }
 
     fun run(): ServerHandle {
+        OtelSdkIntegration.initialize(cfg.isEnableTelemetry)
         // Create the multithreaded event loops for the server
         val bossGroup = MultiThreadIoEventLoopGroup(1, NioIoHandler.newFactory())
         val channelFactory = ChannelFactory<SocketChannel> { NioSocketChannel() }

rbcs-server/src/main/kotlin/net/woggioni/rbcs/server/configuration/Parser.kt

@@ -46,6 +46,8 @@ object Parser {
         var groups = emptyMap<String, Group>()
         var tls: Tls? = null
         val serverPath = root.renderAttribute("path")
+        var enableTelemetry = root.renderAttribute("enable-telemetry")
+            ?.let(String::toBoolean) ?: false
         var incomingConnectionsBacklogSize = 1024
         var authentication: Authentication? = null
         for (child in root.asIterable()) {
@@ -233,6 +235,7 @@ object Parser {
             }
         }
         return Configuration.of(
+            enableTelemetry,
             host,
             port,
             proxyProtocolEnabled,

rbcs-server/src/main/kotlin/net/woggioni/rbcs/server/configuration/Serializer.kt

@@ -29,6 +29,7 @@ object Serializer {
                 ?.let { serverPath ->
                 attr("path", serverPath)
             }
+            attr("enable-telemetry", conf.isEnableTelemetry.toString())
             node("bind") {
                 attr("host", conf.host)
                 attr("port", conf.port.toString())

rbcs-server/src/main/kotlin/net/woggioni/rbcs/server/otel/OtelIntegration.kt

@@ -0,0 +1,32 @@
+package net.woggioni.rbcs.server.otel
+
+import io.netty.channel.ChannelHandler
+import io.opentelemetry.api.GlobalOpenTelemetry
+import io.opentelemetry.instrumentation.netty.v4_1.NettyServerTelemetry
+import net.woggioni.rbcs.common.createLogger
+import net.woggioni.rbcs.common.warn
+
+object OtelIntegration {
+
+    private val log = createLogger<OtelIntegration>()
+
+    val isAvailable: Boolean by lazy {
+        runCatching {
+            Class.forName("io.opentelemetry.api.OpenTelemetry")
+        }.fold(
+            onSuccess = { true },
+            onFailure = {
+                log.warn { "OpenTelemetry classes not on classpath, instrumentation disabled" }
+                false
+            },
+        )
+    }
+
+    fun createHandler(enabled: Boolean): ChannelHandler? {
+        return if (enabled && isAvailable) createHandlerInternal() else null
+    }
+
+    private fun createHandlerInternal(): ChannelHandler {
+        return NettyServerTelemetry.create(GlobalOpenTelemetry.get()).createCombinedHandler()
+    }
+}

rbcs-server/src/main/kotlin/net/woggioni/rbcs/server/otel/OtelSdkIntegration.kt

@@ -0,0 +1,58 @@
+package net.woggioni.rbcs.server.otel
+
+import net.woggioni.rbcs.common.createLogger
+import net.woggioni.rbcs.common.info
+
+object OtelSdkIntegration {
+
+    private val log = createLogger<OtelSdkIntegration>()
+
+    private val isAvailable: Boolean by lazy {
+        runCatching {
+            Class.forName("io.opentelemetry.sdk.autoconfigure.AutoConfiguredOpenTelemetrySdk")
+        }.fold(
+            onSuccess = { true },
+            onFailure = {
+                log.info { "OpenTelemetry SDK autoconfigure not on classpath" }
+                false
+            },
+        )
+    }
+
+    private val appenderAvailable: Boolean by lazy {
+        runCatching {
+            Class.forName("io.opentelemetry.instrumentation.logback.appender.v1_0.OpenTelemetryAppender")
+        }.fold(
+            onSuccess = { true },
+            onFailure = {
+                log.info { "OpenTelemetry logback appender not on classpath" }
+                false
+            },
+        )
+    }
+
+    fun initialize(enabled: Boolean) {
+        if (!enabled || !isAvailable) return
+
+        log.info { "Initializing OpenTelemetry SDK with auto-configuration" }
+
+        val sdk = io.opentelemetry.sdk.autoconfigure.AutoConfiguredOpenTelemetrySdk.builder()
+            .setResultAsGlobal()
+            .build()
+            .openTelemetrySdk
+
+        if (appenderAvailable) {
+            runCatching {
+                val clazz = Class.forName("io.opentelemetry.instrumentation.logback.appender.v1_0.OpenTelemetryAppender")
+                clazz.getMethod("install", Class.forName("io.opentelemetry.api.OpenTelemetry"))
+                    .invoke(null, sdk)
+                log.info { "OpenTelemetry logback appender installed" }
+            }.onFailure { ex ->
+                val msg = ex.localizedMessage ?: ex.javaClass.name
+                log.info { "Failed to install OpenTelemetry logback appender: $msg" }
+            }
+        }
+
+        log.info { "OpenTelemetry SDK initialized successfully" }
+    }
+}

rbcs-server/src/main/resources/net/woggioni/rbcs/server/rbcs-default.xml

@@ -2,7 +2,8 @@
 <rbcs:server
              xmlns:xs="http://www.w3.org/2001/XMLSchema-instance"
              xmlns:rbcs="urn:net.woggioni.rbcs.server"
-             xs:schemaLocation="urn:net.woggioni.rbcs.server jpms://net.woggioni.rbcs.server/net/woggioni/rbcs/server/schema/rbcs-server.xsd">
+             xs:schemaLocation="urn:net.woggioni.rbcs.server jpms://net.woggioni.rbcs.server/net/woggioni/rbcs/server/schema/rbcs-server.xsd"
+             enable-telemetry="false">
     <bind host="127.0.0.1" port="8080" incoming-connections-backlog-size="1024"/>
     <cache xs:type="rbcs:fileSystemCacheType" path="${sys:java.io.tmpdir}/rbcs" max-age="P7D"/>
 </rbcs:server>

rbcs-server/src/main/resources/net/woggioni/rbcs/server/schema/rbcs-server.xsd

@@ -59,6 +59,14 @@
                 </xs:documentation>
             </xs:annotation>
         </xs:attribute>
+        <xs:attribute name="enable-telemetry" type="xs:boolean" use="optional" default="false">
+            <xs:annotation>
+                <xs:documentation>
+                    Enable OpenTelemetry distributed tracing for the server.
+                    Even when enabled, telemetry only activates if OpenTelemetry classes are present on the classpath.
+                </xs:documentation>
+            </xs:annotation>
+        </xs:attribute>
     </xs:complexType>
 
     <xs:complexType name="bindType">

rbcs-server/src/test/kotlin/net/woggioni/rbcs/server/test/AbstractBasicAuthServerTest.kt

@@ -32,6 +32,7 @@ abstract class AbstractBasicAuthServerTest : AbstractServerTest() {
     override fun setUp() {
         this.cacheDir = testDir.resolve("cache")
         cfg = Configuration.of(
+            false,
             "127.0.0.1",
             getFreePort(),
             false,

rbcs-server/src/test/kotlin/net/woggioni/rbcs/server/test/AbstractTlsServerTest.kt

@@ -138,6 +138,7 @@ abstract class AbstractTlsServerTest : AbstractServerTest() {
         this.cacheDir = testDir.resolve("cache")
         createKeyStoreAndTrustStore()
         cfg = Configuration(
+            false,
             "127.0.0.1",
             getFreePort(),
             false,

rbcs-server/src/test/kotlin/net/woggioni/rbcs/server/test/NoAuthServerTest.kt

@@ -32,6 +32,7 @@ class NoAuthServerTest : AbstractServerTest() {
     override fun setUp() {
         this.cacheDir = testDir.resolve("cache")
         cfg = Configuration(
+            false,
             "127.0.0.1",
             getFreePort(),
             false,