A Log4j 2 Appender for Redis.
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README.md

Build 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.

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

License

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/.