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

<dependency>
    <groupId>com.vlkan.log4j2</groupId>
    <artifactId>log4j2-redis-appender</artifactId>
    <version>${log4j2-redis-appender.version}</version>
</dependency>

together with a valid log4j-core dependency:

<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>${log4j2.version}</version>
</dependency>

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

<?xml version="1.0" encoding="UTF-8"?>
<Configuration name="RedisAppenderTest">
    <Appenders>
        <RedisAppender name="REDIS"
                       key="log4j2-messages"
                       host="localhost"
                       port="6379">
            <PatternLayout pattern="%level %msg"/>
            <RedisConnectionPoolConfig testWhileIdle="true"
                                       minEvictableIdleTimeMillis="60000"
                                       timeBetweenEvictionRunsMillis="30000"
                                       numTestsPerEvictionRun="-1"/>
            <RedisThrottlerConfig bufferSize="500"
                                  batchSize="100"
                                  flushPeriodMillis="1000"
                                  maxByteCountPerSecond="100"/>
        </RedisAppender>
    </Appenders>
    <Loggers>
        <Root level="all">
            <AppenderRef ref="REDIS"/>
        </Root>
    </Loggers>
</Configuration>

RedisAppender is configured with the following parameters:

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

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:

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

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] [tst-store-001.data] uncaught exception in thread [commons-pool-EvictionTimer]
  java.security.AccessControlException: access denied ("java.lang.RuntimePermission" "setContextClassLoader")
          at java.security.AccessControlContext.checkPermission(AccessControlContext.java:472) ~[?:1.8.0_131]
          at java.security.AccessController.checkPermission(AccessController.java:884) ~[?:1.8.0_131]
          at java.lang.SecurityManager.checkPermission(SecurityManager.java:549) ~[?:1.8.0_131]
          at java.lang.Thread.setContextClassLoader(Thread.java:1474) [?:1.8.0_131]
          at org.apache.commons.pool2.impl.BaseGenericObjectPool$Evictor.run(BaseGenericObjectPool.java:1052) ~[log4j2-redis-appender.jar:?]
          at java.util.TimerThread.mainLoop(Timer.java:555) ~[?:1.8.0_131]
          at java.util.TimerThread.run(Timer.java:505) ~[?: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, -Djava.security.policy=someURL.

Copyright © 2017 Volkan Yazıcı

log4j2-redis-appender is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

log4j2-redis-appender is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.