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Configuring Logging

Hazelcast has a flexible logging configuration and does not depend on any logging framework except JDK logging. It has built-in adapters for a number of logging frameworks and it also supports custom loggers by providing logging interfaces.

Logging for Member

By default, a Hazelcast member writes logs into the logs directory of the distribution. The logs are configured to roll over daily. You can change the logging configuration by modifying config/log4j.properties.

To use the built-in adapters, set the hazelcast.logging.type property to one of the predefined types below:

  • jdk: JDK logging (default)

  • log4j: Log4j

  • log4j2: Log4j2

  • slf4j: Slf4j

  • none: disable logging

You can set hazelcast.logging.type through declarative configuration, programmatic configuration or JVM system property.

If you choose to use log4j, log4j2, or slf4j, you should include the proper dependencies in the classpath.

Declarative Configuration:

  • XML

  • YAML

        <property name="hazelcast.logging.type">log4j</property>
    hazelcast.logging.type: log4j

Programmatic Configuration

Config config = new Config() ;
config.setProperty( "hazelcast.logging.type", "log4j" );

System Property

  • using the java -Dhazelcast.logging.type=slf4j JVM parameter

  • using the System.setProperty( "hazelcast.logging.type", "none" ); system class

Logging for Client and Embedded Mode

When using Hazelcast through the client or in embedded mode, Hazelcast doesn’t automatically add any dependencies to any logging framework and allows configuration of which facade the logging should be done through.

To configure the logging facade to use, you need to set a property in the configuration file:

    hazelcast.logging.type: log4j2

Alternatively, you can use the system property -Dhazelcast.logging.type to configure the logging framework to use.

Using a Custom Logger

If the provided logging mechanisms are not satisfactory, you can implement your own using the custom logging feature. To use it, implement the com.hazelcast.logging.LoggerFactory and com.hazelcast.logging.ILogger interfaces and set the system property hazelcast.logging.class as your custom LoggerFactory class name.


Listening to Logging Events

You can also listen to logging events generated by Hazelcast runtime by registering LogListeners to LoggingService.

LogListener listener = new LogListener() {
  public void log( LogEvent logEvent ) {
    // do something
HazelcastInstance instance = Hazelcast.newHazelcastInstance();
LoggingService loggingService = instance.getLoggingService();
loggingService.addLogListener( Level.INFO, listener );

Through the LoggingService, you can get the currently used ILogger implementation and log your own messages too.

If you are not using command line for configuring logging, you should be careful about Hazelcast classes. They may be defaulted to jdk logging before newly configured logging is read. When logging mechanism is selected, it will not change.

Changing Log Levels for JDK Logging

As mentioned in the introduction of this section above, the default logging type of Hazelcast is JDK logging. The default logging level is INFO. To change the level in case you want to use the default logging, you can take the following snippet as a reference:

java.util.logging.Logger rootLogger = LogManager.getLogManager().getLogger("");
for (Handler h : rootLogger.getHandlers()) {

Dynamically Changing Log Levels

You can change log levels without the need of restarting the cluster members. This may be useful while monitoring or diagnosing the events in your cluster.

This feature is supported for the default (JDK/JUL), Log4j, and Log4j2 frameworks. The Slf4j framework is not supported since it does not provide any log level changing APIs.

You can use either of the following ways to dynamically change the level of your cluster’s logs:

  • Using JMX API: The logging service exposes its JMX MBean as LoggingServiceMBean. You can retrieve, set, and reset the level. See the Monitoring with JMX section.

  • Using REST API: You can use the /hazelcast/rest/log-level REST endpoint to retrieve (GET), set (POST), and reset (DELETE) the level. See the REST Endpoint Groups section.

Example Configuration Files

Below are example configurations for Log4j2 and Log4j. Note that Hazelcast does not recommend any specific logging library, these examples are provided only to demonstrate how to configure the logging. You can use your custom logging as explained above.

First, specify the logging type as Log4j2 or Log4j and a separate logging configuration file as shown below.

Using JVM arguments:

-Dhazelcast.logging.type=log4j2 (or log4j)
-Dlog4j.configurationFile=/path/to/properties/log4j2.properties (or log4j)

Using declarative configuration (hazelcast.xml/yaml):

  • XML

  • YAML

        <property name="hazelcast.logging.type">log4j2</property>
    hazelcast.logging.type: log4j2
Specifying a separated configuration file is only possible using the JVM argument approach as shown above.

Following is an example log4j2.properties file:


appenders = console, file

appender.console.type = Console
appender.console.name = STDOUT
appender.console.layout.type = PatternLayout
appender.console.layout.pattern = %d{yyyy-MM-dd HH:mm:ss} %-5p %c\{1}:%L - %m%n
appender.file.layout.pattern = %d{yyyy-MM-dd HH:mm:ss} %-5p %c\{1}:%L - %m%n

rootLogger.appenderRefs= STDOUT
rootLogger.appenderRef.stdout.ref = STDOUT

#Hazelcast specific logs.


To enable the debug logs for all Hazelcast operations uncomment the below line in the above configuration file:


If you do not need detailed logs, the default settings are enough. Using the Hazelcast specific lines in the above configuration file, you can select to see specific logs (cluster, partition, hibernate, etc.) in desired levels.

You can also use the hazelcast.logging.details.enabled property to specify whether the name, IP address and version of the cluster are included in the logs. When there are lots of log lines, it may be hard to follow. When set to false, those information will not appear.

And, the following is an example log4j.properties file:


log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %p [%c\{1}] - %m%n