Relaxed kafka appender for search-service logback (#1466)

ansible/roles/stack-sunbird/templates/search-service_logback.xml

@@ -32,26 +32,24 @@
 
 		<topic>{{env_name}}.telemetry.raw</topic>
 		<!-- ensure that every message sent by the executing host is partitioned to the same partition strategy -->
-        <keyingStrategy class="com.github.danielwegener.logback.kafka.keying.HostNameKeyingStrategy" />
+        <keyingStrategy class="com.github.danielwegener.logback.kafka.keying.NoKeyKeyingStrategy" />
         <!-- block the logging application thread if the kafka appender cannot keep up with sending the log messages -->
-        <deliveryStrategy class="com.github.danielwegener.logback.kafka.delivery.BlockingDeliveryStrategy">
-            <!-- wait indefinitely until the kafka producer was able to send the message -->
-            <timeout>0</timeout>
-        </deliveryStrategy>
-		
+        <deliveryStrategy class="com.github.danielwegener.logback.kafka.delivery.AsynchronousDeliveryStrategy" />
+        
 		<!-- each <producerConfig> translates to regular kafka-client config (format: key=value) -->
-		<!-- producer configs are documented here: https://kafka.apache.org/documentation.html#newproducerconfigs -->
-		<!-- bootstrap.servers is the only mandatory producerConfig -->
-		<producerConfig>bootstrap.servers={{lp_kafka_url}}</producerConfig>
-		<!-- restrict the size of the buffered batches to 8MB (default is 32MB) -->
-        <producerConfig>buffer.memory=8388608</producerConfig>
-
-        <!-- If the kafka broker is not online when we try to log, just block until it becomes available -->
-        <producerConfig>metadata.fetch.timeout.ms=99999999999</producerConfig>
+        <!-- producer configs are documented here: https://kafka.apache.org/documentation.html#newproducerconfigs -->
+        <!-- bootstrap.servers is the only mandatory producerConfig -->
+        <producerConfig>bootstrap.servers={{lp_kafka_url}}</producerConfig>
+        <!-- don't wait for a broker to ack the reception of a batch.  -->
+        <producerConfig>acks=0</producerConfig>
+        <!-- wait up to 1000ms and collect log messages before sending them as a batch -->
+        <producerConfig>linger.ms=15000</producerConfig>
+        <!-- even if the producer buffer runs full, do not block the application but start to drop messages -->
+        <producerConfig>max.block.ms=0</producerConfig>
         <!-- define a client-id that you use to identify yourself against the kafka broker -->
-        <producerConfig>client.id=${HOSTNAME}-${CONTEXT_NAME}-logback-restrictive</producerConfig>
-        <!-- Log every log message that could not be sent to kafka to STDERR -->
-        <appender-ref ref="ASYNCSTDOUT"/>
+        <producerConfig>client.id=${HOSTNAME}-${CONTEXT_NAME}-logback-relaxed</producerConfig>
+
+        <!-- there is no fallback <appender-ref>. If this appender cannot deliver, it will drop its messages. -->
 
 	</appender>