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

Usage

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"
                                  maxEventCountPerSecond="100"
                                  maxByteCountPerSecond="4194304"/>
        </RedisAppender>
    </Appenders>
    <Loggers>
        <Root level="all">
            <AppenderRef ref="REDIS"/>
        </Root>
    </Loggers>
</Configuration>

RedisAppender is configured with the following parameters:

Parameter Name	Type	Default	Description
charset	String	UTF-8	output charset
key	String		Redis queue key
host	String	localhost	Redis host
port	int	6379	Redis port
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
debugEnabled	boolean	false	enables logging to stderr for debugging the plugin

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)
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.

Fat JAR

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.

F.A.Q.

• 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.

• 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.

Contributors

• t9t
• Yaroslav Skopets

License

Copyright © 2017-2019 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

http://www.apache.org/licenses/LICENSE-2.0

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.