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 = 2026.04.14
 
 gitea.maven.url = https://gitea.woggioni.net/api/packages/woggioni/maven
 docker.registry.url=gitea.woggioni.net

rbcs-server/build.gradle

@@ -13,6 +13,7 @@ dependencies {
     implementation catalog.netty.buffer
     implementation catalog.netty.transport
     implementation catalog.netty.codec.haproxy
+    compileOnly catalog.opentelemetry.netty['4']['1']
 
     api project(':rbcs-common')
     api project(':rbcs-api')

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

@@ -17,6 +17,8 @@ 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 org.slf4j;
 
     exports net.woggioni.rbcs.server;

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

@@ -68,6 +68,7 @@ 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.auth.AbstractNettyHttpAuthenticator
 import net.woggioni.rbcs.server.auth.Authorizer
 import net.woggioni.rbcs.server.auth.RoleAuthorizer
@@ -431,6 +432,7 @@ class RemoteBuildCacheServer(private val cfg: Configuration) {
                 maxChunkSize = cfg.connection.chunkSize
             }
             pipeline.addLast(HttpServerCodec(httpDecoderConfig))
+            OtelIntegration.createHandler()?.let { pipeline.addLast(it) }
             pipeline.addLast(ReadTriggerDuplexHandler.NAME, ReadTriggerDuplexHandler())
             pipeline.addLast(MaxRequestSizeHandler.NAME, MaxRequestSizeHandler(cfg.connection.maxRequestSize))
             pipeline.addLast(HttpChunkContentCompressor(1024))

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(): ChannelHandler? {
+        return if (isAvailable) createHandlerInternal() else null
+    }
+
+    private fun createHandlerInternal(): ChannelHandler {
+        return NettyServerTelemetry.create(GlobalOpenTelemetry.get()).createCombinedHandler()
+    }
+}