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.

Locating the Logs

If you start a member using the hz-start script from the Hazelcast distribution package, the logs are written to <HAZELCAST HOME>/logs directory by default. The logs are configured to roll over daily. Note that the logs are also shown in the terminal where you start the member while it is up and running.

In case you use Docker to start a member, the logs are written to stdout. You can use the docker logs <Hazelcast container ID> command to see the member logs at any point in time. The container ID can be seen using docker ps. You can also use docker logs -f <Hazelcast container ID> to follow the logs in real-time.

Setting Logging Type

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

The following shows how you can set this property:

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

YAML
XML
Java member API
JVM
System Property

hazelcast:
  properties:
    hazelcast.logging.type: log4j2yaml

<hazelcast>
    ...
    <properties>
        <property name="hazelcast.logging.type">log4j2</property>
    </properties>
    ...
</hazelcast>xml

Config config = new Config() ;
config.setProperty( "hazelcast.logging.type", "log4j2" );

java -Dhazelcast.logging.type=log4jshell

System.setProperty( "hazelcast.logging.type", "log4j" );shell

Logging Pattern

The default log output resembles the following example:

2022-02-16 11:40:52,463 [ INFO] [main] [c.h.system]: [172.18.0.2]:5701 [hello-world] [5.2.5] Copyright (c) 2008-2022, Hazelcast, Inc. All Rights Reserved.
2022-02-16 11:40:52,463 [ INFO] [main] [c.h.system]: [172.18.0.2]:5701 [hello-world] [5.2.5] Hazelcast Platform 5.2.5 (20220210 - 1d718cf) starting at [172.18.0.2]:5701
2022-02-16 11:40:52,463 [ INFO] [main] [c.h.system]: [172.18.0.2]:5701 [hello-world] [5.2.5] Cluster name: hello-worldbash

The logging pattern is shown below.

[Date and time] [Log level] [Thread name] [Logger Class Name] [Member IP and port] [Cluster name] [Platform version] [Log message]plain

You can customize the default logging pattern using the LOGGING_PATTERN environment variable while starting a member.

Here is an example usage.

CLI
Docker

LOGGING_PATTERN='{"time":"%date{ISO8601}", "logger": "%logger{36}", "level": "%level", "msg": "%enc{%m %xEx}{JSON}"}%n' bin/hz startbash

docker run \
    -e LOGGING_PATTERN='{"time":"%date{ISO8601}", "logger": "%logger{36}", "level": "%level", "msg": "%enc{%m %xEx}{JSON}"}%n' \
    hazelcast/hazelcast:5.2.5bash

Specifying Logging Configuration File

You can specify the logging configuration file using the LOGGING_CONFIG environment variable. If it is not set, the default <HAZELCAST HOME>/config/log4j2.properties is used; you can change the logging configuration by modifying this file.

Here is an example usage.

CLI
Docker

Provide the file’s relative or absolute path, or a file in the <HAZELCAST HOME>/config directory.

LOGGING_CONFIG=config/myHzConfig.properties bin/hz startbash

Provide the file’s relative or absolute path.

docker run \
    -e LOGGING_CONFIG=config/myHzConfig.properties \
    hazelcast/hazelcast:5.2.5bash

You can also provide a properties file having a path of your choice. For Log4j2, you can specify this using the following JVM argument (which is the only way for Log4j2).

-Dlog4j.configurationFile=/path/to/properties/log4j2.properties

Modifying the Default Logging

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

...
...
#Hazelcast specific logs.
#logger.com.hazelcast=debug

#logger.com.hazelcast.cluster=debug
#logger.com.hazelcast.partition=debug
...
....shell

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

logger.com.hazelcast=debug

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.

Using JSON Template

You can use JSON templates for the member log files. The JSON logging configuration file built on the default JSON template layout is <HAZELCAST HOME>/config/log4j2-json.properties.

You can use a different JSON template via the LOGGING_JSON_TEMPLATE environment variable. Here is an example usage.

CLI
Docker

LOGGING_CONFIG=log4j2-json.properties LOGGING_JSON_TEMPLATE="classpath:EcsLayout.json" bin/hz startbash

docker run \
    -e LOGGING_CONFIG=config/log4j2-json.properties \
    -e LOGGING_JSON_TEMPLATE="classpath:EcsLayout.json" \
    hazelcast/hazelcast:5.2.5bash

See Event Templates for available templates.

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.

You can change the JDK logging level as follows while starting a member.

Docker
Java member API

docker run \
    -e LOGGING_LEVEL=FINE \
    hazelcast/hazelcast:5.2.5bash

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

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.

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-client:
  properties:
    hazelcast.logging.type: log4j2yaml

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.

-Dhazelcast.logging.class=foo.bar.MyLoggingFactory

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 );java

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.