Add OpenTelemetry tracing support for Redis commands

- Add RedisSpan interface in rbcs-api for opaque span handles
- Extend TelemetryController with startRedisSpan/endRedisSpan methods
- Implement Redis tracing in rbcs-server-otel via OtelController and RedisOtelSpan
- Instrument RedisCacheHandler to create spans around GET and SET commands
- Add uses directive in rbcs-server-redis module-info for ServiceLoader discovery

Redis spans are created as CLIENT spans with attributes:
db.system=redis, db.operation=GET|SET, server.address, server.port

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

@@ -0,0 +1,10 @@
+package net.woggioni.rbcs.api;
+
+import org.jetbrains.annotations.NotNull;
+
+public interface RedisSpan {
+
+    void setAttribute(@NotNull String key, @NotNull String value);
+
+    void setAttribute(@NotNull String key, long value);
+}

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

@@ -2,8 +2,15 @@ package net.woggioni.rbcs.api;
 
 import io.netty.channel.ChannelHandler;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 public interface TelemetryController {
     void initialize();
     @NotNull ChannelHandler createHandler();
+
+    @Nullable RedisSpan startRedisSpan(@NotNull String command, @NotNull String key);
+
+    void endRedisSpan(@Nullable RedisSpan span);
+
+    void endRedisSpan(@Nullable RedisSpan span, @NotNull Throwable error);
 }

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

@@ -2,10 +2,13 @@ package net.woggioni.rbcs.server.otel
 
 import io.netty.channel.ChannelHandler
 import io.opentelemetry.api.GlobalOpenTelemetry
+import io.opentelemetry.api.trace.SpanKind
+import io.opentelemetry.api.trace.StatusCode
 import io.opentelemetry.instrumentation.logback.appender.v1_0.OpenTelemetryAppender
 import io.opentelemetry.instrumentation.netty.v4_1.NettyServerTelemetry
 import io.opentelemetry.instrumentation.runtimetelemetry.RuntimeTelemetry
 import io.opentelemetry.sdk.autoconfigure.AutoConfiguredOpenTelemetrySdk
+import net.woggioni.rbcs.api.RedisSpan
 import net.woggioni.rbcs.api.TelemetryController
 import net.woggioni.rbcs.common.createLogger
 import net.woggioni.rbcs.common.info
@@ -14,6 +17,10 @@ class OtelController : TelemetryController {
 
     private val log = createLogger<OtelController>()
 
+    private val tracer by lazy {
+        GlobalOpenTelemetry.getTracer("net.woggioni.rbcs.server.redis", "0.5.0")
+    }
+
     override fun initialize() {
         log.info { "Initializing OpenTelemetry SDK with auto-configuration" }
 
@@ -36,4 +43,24 @@ class OtelController : TelemetryController {
     override fun createHandler(): ChannelHandler {
         return NettyServerTelemetry.create(GlobalOpenTelemetry.get()).createCombinedHandler()
     }
+
+    override fun startRedisSpan(command: String, key: String): RedisSpan? {
+        val span = tracer.spanBuilder(command)
+            .setSpanKind(SpanKind.CLIENT)
+            .setAttribute("db.system", "redis")
+            .setAttribute("db.operation", command)
+            .startSpan()
+        return RedisOtelSpan(span)
+    }
+
+    override fun endRedisSpan(span: RedisSpan?) {
+        (span as? RedisOtelSpan)?.delegate?.end()
+    }
+
+    override fun endRedisSpan(span: RedisSpan?, error: Throwable) {
+        val s = (span as? RedisOtelSpan)?.delegate ?: return
+        s.recordException(error)
+        s.setStatus(StatusCode.ERROR)
+        s.end()
+    }
 }

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

@@ -0,0 +1,17 @@
+package net.woggioni.rbcs.server.otel
+
+import io.opentelemetry.api.trace.Span
+import net.woggioni.rbcs.api.RedisSpan
+
+internal class RedisOtelSpan(
+    val delegate: Span,
+) : RedisSpan {
+
+    override fun setAttribute(key: String, value: String) {
+        delegate.setAttribute(key, value)
+    }
+
+    override fun setAttribute(key: String, value: Long) {
+        delegate.setAttribute(key, value)
+    }
+}

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

@@ -1,4 +1,5 @@
 import net.woggioni.rbcs.api.CacheProvider;
+import net.woggioni.rbcs.api.TelemetryController;
 
 module net.woggioni.rbcs.server.redis {
     requires net.woggioni.rbcs.common;
@@ -16,5 +17,7 @@ module net.woggioni.rbcs.server.redis {
 
     provides CacheProvider with net.woggioni.rbcs.server.redis.RedisCacheProvider;
 
+    uses TelemetryController;
+
     opens net.woggioni.rbcs.server.redis.schema;
 }

rbcs-server-redis/src/main/kotlin/net/woggioni/rbcs/server/redis/RedisCacheHandler.kt

@@ -3,6 +3,7 @@ package net.woggioni.rbcs.server.redis
 import java.io.ByteArrayOutputStream
 import java.io.ObjectInputStream
 import java.io.ObjectOutputStream
+import java.net.InetSocketAddress
 import java.nio.ByteBuffer
 import java.nio.channels.Channels
 import java.nio.channels.FileChannel
@@ -35,8 +36,11 @@ import net.woggioni.rbcs.api.message.CacheMessage.CachePutResponse
 import net.woggioni.rbcs.api.message.CacheMessage.CacheValueFoundResponse
 import net.woggioni.rbcs.api.message.CacheMessage.CacheValueNotFoundResponse
 import net.woggioni.rbcs.api.message.CacheMessage.LastCacheContent
+import net.woggioni.rbcs.api.RedisSpan
+import net.woggioni.rbcs.api.TelemetryController
 import net.woggioni.rbcs.common.ByteBufInputStream
 import net.woggioni.rbcs.common.ByteBufOutputStream
+import net.woggioni.rbcs.common.RBCS.loadService
 import net.woggioni.rbcs.common.RBCS.processCacheKey
 import net.woggioni.rbcs.common.RBCS.toIntOrNull
 import net.woggioni.rbcs.common.createLogger
@@ -60,6 +64,10 @@ class RedisCacheHandler(
         private val log = createLogger<RedisCacheHandler>()
     }
 
+    private val telemetryController by lazy {
+        loadService(TelemetryController::class.java).firstOrNull()
+    }
+
     private interface InProgressRequest
 
     private inner class InProgressGetRequest(
@@ -242,8 +250,10 @@ class RedisCacheHandler(
         }
         val keyBytes = processCacheKey(msg.key, keyPrefix, digestAlgorithm)
         val keyString = String(keyBytes, StandardCharsets.UTF_8)
+        val redisSpan = telemetryController?.startRedisSpan("GET", keyString)
         val responseHandler = object : RedisResponseHandler {
             override fun responseReceived(response: RedisMessage) {
+                try {
                     when (response) {
                         is FullBulkStringRedisMessage -> {
                             if (response === FullBulkStringRedisMessage.NULL_INSTANCE || response.content().readableBytes() == 0) {
@@ -263,9 +273,9 @@ class RedisCacheHandler(
                         }
 
                         is ErrorRedisMessage -> {
-                        this@RedisCacheHandler.exceptionCaught(
+                            val ex = RedisException("Redis error for GET ${msg.key}: ${response.content()}")
-                            ctx, RedisException("Redis error for GET ${msg.key}: ${response.content()}")
+                            telemetryController?.endRedisSpan(redisSpan, ex)
-                        )
+                            this@RedisCacheHandler.exceptionCaught(ctx, ex)
                         }
 
                         else -> {
@@ -275,13 +285,22 @@ class RedisCacheHandler(
                             sendMessageAndFlush(ctx, CacheValueNotFoundResponse(msg.key))
                         }
                     }
+                } finally {
+                    telemetryController?.endRedisSpan(redisSpan)
+                }
             }
 
             override fun exceptionCaught(ex: Throwable) {
+                telemetryController?.endRedisSpan(redisSpan, ex)
                 this@RedisCacheHandler.exceptionCaught(ctx, ex)
             }
         }
         client.sendCommand(keyBytes, ctx.alloc(), responseHandler).thenAccept { channel ->
+            val remoteAddr = channel.remoteAddress()
+            if (remoteAddr is InetSocketAddress) {
+                remoteAddr.hostString?.let { redisSpan?.setAttribute("server.address", it) }
+                redisSpan?.setAttribute("server.port", remoteAddr.port.toLong())
+            }
             log.trace(ctx) {
                 "Sending GET request for key ${msg.key} to Redis"
             }
@@ -342,8 +361,11 @@ class RedisCacheHandler(
 
                 val expirySeconds = maxAge.toSeconds().toString()
 
+                val redisSpan = telemetryController?.startRedisSpan("SET", request.keyString)
+
                 val responseHandler = object : RedisResponseHandler {
                     override fun responseReceived(response: RedisMessage) {
+                        try {
                             when (response) {
                                 is SimpleStringRedisMessage -> {
                                     log.debug(ctx) {
@@ -353,26 +375,35 @@ class RedisCacheHandler(
                                 }
 
                                 is ErrorRedisMessage -> {
-                                this@RedisCacheHandler.exceptionCaught(
+                                    val ex = RedisException("Redis error for SET ${request.keyString}: ${response.content()}")
-                                    ctx, RedisException("Redis error for SET ${request.keyString}: ${response.content()}")
+                                    telemetryController?.endRedisSpan(redisSpan, ex)
-                                )
+                                    this@RedisCacheHandler.exceptionCaught(ctx, ex)
                                 }
 
                                 else -> {
-                                this@RedisCacheHandler.exceptionCaught(
+                                    val ex = RedisException("Unexpected response for SET ${request.keyString}: ${response.javaClass.name}")
-                                    ctx, RedisException("Unexpected response for SET ${request.keyString}: ${response.javaClass.name}")
+                                    telemetryController?.endRedisSpan(redisSpan, ex)
-                                )
+                                    this@RedisCacheHandler.exceptionCaught(ctx, ex)
                                 }
                             }
+                        } finally {
+                            telemetryController?.endRedisSpan(redisSpan)
+                        }
                     }
 
                     override fun exceptionCaught(ex: Throwable) {
+                        telemetryController?.endRedisSpan(redisSpan, ex)
                         this@RedisCacheHandler.exceptionCaught(ctx, ex)
                     }
                 }
 
                 // Use a ByteBuf key for server selection
                 client.sendCommand(keyBytes, ctx.alloc(), responseHandler).thenAccept { channel ->
+                    val remoteAddr = channel.remoteAddress()
+                    if (remoteAddr is InetSocketAddress) {
+                        remoteAddr.hostString?.let { redisSpan?.setAttribute("server.address", it) }
+                        redisSpan?.setAttribute("server.port", remoteAddr.port.toLong())
+                    }
                     log.trace(ctx) {
                         "Sending SET request to Redis"
                     }