Skip to content


Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?

Latest commit


Git stats


Failed to load latest commit information.
Latest commit message
Commit time

Actions Status Maven Central License

RedisAppender plugin provides a Log4j 2.x appender for Redis in-memory data structure store. The plugin uses Jedis as a client for Redis.


Add the log4j2-redis-appender dependency to your POM file


together with a valid log4j-core dependency:


Below you can find a sample log4j2.xml snippet employing RedisAppender.

<?xml version="1.0" encoding="UTF-8"?>
        <RedisAppender name="REDIS"
            <PatternLayout pattern="%level %msg"/>
            <RedisConnectionPoolConfig testWhileIdle="true"
            <RedisThrottlerConfig bufferSize="500"
        <Root level="all">
            <AppenderRef ref="REDIS"/>

One can make RedisAppender work against a sentinel setup using sentinelNodes and sentinelMaster parameters:

<RedisAppender name="REDIS"

Note that sentinelNodes and sentinelMaster have priority over host and port parameters.

RedisAppender is configured with the following parameters:

Parameter Name Type Default Description
charset String UTF-8 output charset
database int 0 Redis logical database
key String Redis queue key
host String localhost Redis host
port int 6379 Redis port
sentinelNodes String null Redis sentinel nodes as comma-separated list, e.g., host1:port1,host2:port2. If specified, host and port parameters are ignored.
sentinelMaster String null Redis sentinel master name
password String null Redis password
connectionTimeoutSeconds int 2 initial connection timeout in seconds
socketTimeoutSeconds int 2 socket timeout in seconds
ignoreExceptions boolean true Enabling causes exceptions encountered while appending events to be internally logged and then ignored. When set to false, exceptions will be propagated to the caller, instead. You must set this to false when wrapping this appender in a FailoverAppender.
Layout Layout PatternLayout used to format the LogEvents
RedisConnectionPoolConfig RedisConnectionPoolConfig Redis connection pool configuration
RedisThrottlerConfig RedisThrottlerConfig Redis throttler configuration

Redis Connection Pool

RedisConnectionPoolConfig is a wrapper for JedisPoolConfig which extends GenericObjectPoolConfig of Apache Commons Pool. Below is a complete list of available RedisConnectionPoolConfig attributes.

Parameter Name Type Default
maxTotal int 8
maxIdle int 8
minIdle int 0
lifo boolean true
fairness boolean false
maxWaitMillis long -1
minEvictableIdleTimeMillis long 1000 * 60
softMinEvictableIdleTimeMillis long -1
numTestsPerEvictionRun int -1
testOnCreate boolean false
testOnBorrow boolean false
testOnReturn boolean false
testWhileIdle boolean true
timeBetweenEvictionRunsMillis long 1000 * 30
evictionPolicyClassName String org.apache.commons.pool2.impl.DefaultEvictionPolicy
blockWhenExhausted boolean true
jmxEnabled boolean true
jmxNameBase String null
jmxNamePrefix String com.vlkan.log4j2.redis.appender.JedisConnectionPool

Redis Throttler

While Log4j 2 provides utilities like BurstFilter and AsyncAppender that you can wrap around any appender to facilitate throttling, the appender API falls short of communicating this intent. Hence, RedisAppender provides its own throttling mechanics to exploit batch pushes available in Redis RPUSH. This feature is configured by RedisThrottlerConfig element using the following attributes:

Parameter Name Type Description
bufferSize int LogEvent buffer size (defaults to 500)
batchSize int size of batches fed into Redis RPUSH (defaults to 100)
flushPeriodMillis long buffer flush period (defaults to 1000)
maxEventCountPerSecond double allowed maximum number of events per second (defaults to 0, that is, unlimited)
maxByteCountPerSecond double allowed maximum number of bytes per second (defaults to 0, that is, unlimited)
maxErrorCountPerSecond double allowed maximum number of errors per second propagated (defaults to 0.003, that is, approximately once every 5 minutes)
jmxBeanName String RedisThrottlerJmxBean name (defaults to org.apache.logging.log4j2:type=<loggerContextName>,component=Appenders,name=<appenderName>,subtype=RedisThrottler)

The buffer is flushed if either there are more than batchSize events queued in the buffer, or the last flush was older than flushPeriodMillis.

maxErrorCountPerSecond is there to avoid flooding logs if the application is suffering a shortage of memory, or the Redis server is unreachable.


Project also contains a log4j2-redis-appender-fatjar artifact which includes all its transitive dependencies in a separate shaded package (to avoid the JAR Hell) with the exception of log4j-core, that you need to include separately.

This might come handy if you want to use this plugin along with already compiled applications, e.g., Elasticsearch 5.x, which requires Log4j 2.x.


  • How can I connect to multiple Redis servers for failover? You can define multiple Redis appenders nested under a FailoverAppender. (Don't forget to turn off ignoreExceptions flag.)

  • How can I avoid getting AccessControlException exceptions? If you are using the plugin in a security manager enabled Java application (for instance, which is the case for Elasticsearch since version 2.3), you might be getting AccessControlException exceptions as follows:

    [2017-06-23T11:25:35,644][WARN ][o.e.b.ElasticsearchUncaughtExceptionHandler] [] uncaught exception in thread [commons-pool-EvictionTimer] access denied ("java.lang.RuntimePermission" "setContextClassLoader")
            at ~[?:1.8.0_131]
            at ~[?:1.8.0_131]
            at java.lang.SecurityManager.checkPermission( ~[?:1.8.0_131]
            at java.lang.Thread.setContextClassLoader( [?:1.8.0_131]
            at org.apache.commons.pool2.impl.BaseGenericObjectPool$ ~[log4j2-redis-appender.jar:?]
            at java.util.TimerThread.mainLoop( ~[?:1.8.0_131]
            at ~[?:1.8.0_131]

    To alleviate this, you need to grant necessary permissions using a policy file:

    grant {
        permission java.lang.RuntimePermission "setContextClassLoader";

    Then you can activate this policy for your application via either placing it under one of default policy file locations (e.g., $JAVA_HOME/lib/security/java.policy) or providing it as an argument at runtime, that is,

  • How can I access JMX bean of an appender? Once you have a reference to the relevant LoggerContext, you can access the instance of the appender and its JMX bean by its name as follows:

    Appender appender = loggerContext.getConfiguration().getAppender("REDIS");
    RedisThrottlerJmxBean jmxBean = ((RedisAppender) appender).getJmxBean();

    You can either create your own LoggerContext:

    LoggerContextResource loggerContextResource = new LoggerContextResource("/path/to/log4j2.xml");
    LoggerContext loggerContext = loggerContextResource.getLoggerContext();

    or get a handle to an existing one:

     LoggerContext logContext = (LoggerContext) LogManager.getContext(false);

    Here note that you should be using org.apache.logging.log4j.core.LoggerContext, not org.apache.logging.log4j.spi.LoggerContext.


Security policy

If you have encountered an unlisted security vulnerability or other unexpected behaviour that has security impact, please report them privately to the email address.


Copyright © 2017-2023 Volkan Yazıcı

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.