Logback: fix otel appender install for async appenders

instrumentation/logback/logback-appender-1.0/library/build.gradle.kts

@@ -100,6 +100,30 @@ testing {
         }
       }
     }
+
+    val asyncAppenderTest by registering(JvmTestSuite::class) {
+      dependencies {
+        implementation(project(":instrumentation:logback:logback-appender-1.0:library"))
+        implementation("io.opentelemetry:opentelemetry-sdk-testing")
+        implementation(project(":testing-common"))
+
+        if (latestDepTest) {
+          implementation("ch.qos.logback:logback-classic:+")
+        } else {
+          implementation("ch.qos.logback:logback-classic") {
+            version {
+              // first version that has ch.qos.logback.classic.AsyncAppender
+              strictly("1.0.4")
+            }
+          }
+          implementation("org.slf4j:slf4j-api") {
+            version {
+              strictly("1.6.4")
+            }
+          }
+        }
+      }
+    }
   }
 }
 

instrumentation/logback/logback-appender-1.0/library/src/asyncAppenderTest/java/io/opentelemetry/instrumentation/logback/appender/v1_0/AsyncOpenTelemetryAppenderTest.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.instrumentation.logback.appender.v1_0;
+
+import io.opentelemetry.instrumentation.testing.junit.LibraryInstrumentationExtension;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+class AsyncOpenTelemetryAppenderTest {
+  private static final Logger logger = LoggerFactory.getLogger("TestLogger");
+
+  @RegisterExtension
+  private static final LibraryInstrumentationExtension testing =
+      LibraryInstrumentationExtension.create();
+
+  @BeforeEach
+  void setup() {
+    OpenTelemetryAppender.install(testing.getOpenTelemetry());
+  }
+
+  @Test
+  void captureLogMessage() {
+    logger.info("log message 1");
+
+    testing.waitAndAssertLogRecords(logRecord -> logRecord.hasBody("log message 1"));
+  }
+}

instrumentation/logback/logback-appender-1.0/library/src/asyncAppenderTest/resources/logback-test.xml

@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+
+  <appender name="console" class="ch.qos.logback.core.ConsoleAppender">
+    <encoder>
+      <pattern>
+        %d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+      </pattern>
+    </encoder>
+  </appender>
+  <appender name="OpenTelemetry"
+    class="io.opentelemetry.instrumentation.logback.appender.v1_0.OpenTelemetryAppender">
+  </appender>
+
+  <appender name="AsyncAppender" class="ch.qos.logback.classic.AsyncAppender">
+    <appender-ref ref="OpenTelemetry" />
+  </appender>
+
+  <root level="INFO">
+    <appender-ref ref="console"/>
+    <appender-ref ref="AsyncAppender"/>
+  </root>
+
+</configuration>

instrumentation/logback/logback-appender-1.0/library/src/main/java/io/opentelemetry/instrumentation/logback/appender/v1_0/OpenTelemetryAppender.java

@@ -9,7 +9,9 @@
 
 import ch.qos.logback.classic.LoggerContext;
 import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.core.Appender;
 import ch.qos.logback.core.UnsynchronizedAppenderBase;
+import ch.qos.logback.core.spi.AppenderAttachable;
 import io.opentelemetry.api.OpenTelemetry;
 import io.opentelemetry.instrumentation.logback.appender.v1_0.internal.LoggingEventMapper;
 import java.util.ArrayList;
@@ -60,14 +62,17 @@ public static void install(OpenTelemetry openTelemetry) {
     }
     LoggerContext loggerContext = (LoggerContext) loggerFactorySpi;
     for (ch.qos.logback.classic.Logger logger : loggerContext.getLoggerList()) {
-      logger
+      logger.iteratorForAppenders().forEachRemaining(appender -> install(openTelemetry, appender));
+    }
+  }
+
+  private static void install(OpenTelemetry openTelemetry, Appender<?> appender) {
+    if (appender instanceof OpenTelemetryAppender) {
+      ((OpenTelemetryAppender) appender).setOpenTelemetry(openTelemetry);
+    } else if (appender instanceof AppenderAttachable) {
+      ((AppenderAttachable<?>) appender)
           .iteratorForAppenders()
-          .forEachRemaining(
-              appender -> {
-                if (appender instanceof OpenTelemetryAppender) {
-                  ((OpenTelemetryAppender) appender).setOpenTelemetry(openTelemetry);
-                }
-              });
+          .forEachRemaining(a -> OpenTelemetryAppender.install(openTelemetry, a));
     }
   }