Remote Logging

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Overview

Alluxio supports sending logs to a remote log server over the network. This feature can be useful to system administrators who have to perform the task of log collection. With remote logging, the log files, e.g. master.log, worker.log, etc. on all Alluxio servers will be readily available on a designated and configurable directory on the log server. Alternatively, users can use basic logging functions provided by Alluxio rather than using remote logging.

Deploying the Log Server

Configuring the Log Server

You need to specify the directory that the log server will write logs to by setting the ALLUXIO_LOGSERVER_LOGS_DIR environment variable or adding it to ${ALLUXIO_HOME}/conf/alluxio-env.sh.

You can specify ALLUXIO_LOGSERVER_PORT to change the port the log server will be listening to. You can find the default port in table of configuration properties

Start the Log Server

On the log server, execute the following command.

$ ./bin/alluxio-start.sh logserver

Stop the Log Server

$ ./bin/alluxio-stop.sh logserver

Configuring Alluxio Server Processes

By default, remote logging is not enabled. You need to set 2 environment variables in ${ALLUXIO_HOME}/conf/alluxio-env.sh to enable it.

  1. ALLUXIO_LOGSERVER_HOSTNAME specifies the hostname of the remote log server. The equivalent Java opt is alluxio.logserver.hostname.

  2. ALLUXIO_LOGSERVER_PORT specifies the port the remote log server is listening to. The equivalent Java opt is alluxio.logserver.port.

There is no requirement on where the log server can be run, as long as the other Alluxio servers have network access to it. In our example, we run the log server on the same machine as a master.

Enabling Remote Logging with Environment Variables

The two environment variables ALLUXIO_LOGSERVER_HOSTNAME and ALLUXIO_LOGSERVER_PORT control the logging behavior of masters and workers in an Alluxio cluster.

Suppose the hostname of the log server is AlluxioLogServer, and the port is 45600. The following lines would need to be added to conf/alluxio-env.sh to enable remote logging :

ALLUXIO_LOGSERVER_HOSTNAME=AlluxioLogServer
ALLUXIO_LOGSERVER_PORT=45600

These variables propagate their values to the alluxio.logserver.hostname and alluxio.logserver.port [system properties] when set via alluxio-env.sh which are then referenced within log4j.properties

Restart Alluxio and the Log Server

After making the modification to configuration, you need to restart the log server first. Then you can start Alluxio. This ensures that the logs that Alluxio generates during start-up phase will also go to the log server.

Verify the Log Server has Started

SSH to the machine on which log server is running.

Go to the directory where the log server has been configured to store logs received from other Alluxio servers. In the above example, the directory is /tmp/alluxio_remote_logs.

$ cd /tmp/alluxio_remote_logs
$ ls
master          proxy           secondary_master    worker
$ ls -l master/
...
-rw-r--r--  1 alluxio  alluxio  26109 Sep 13 08:49 34.204.198.64.log
...

You can see that the log files are put into different folders according to their type. Master logs are put in the folder master, worker logs are put in folder worker, etc. Within each folder, log files from different workers are distinguished by the IP/hostname of the machine on which the server has been running.

Control Remote Logging Behavior with log4j.properties

The remote log server uses the default threshold of WARN, which means log4j levels below WARN will not be sent to the remote log server. This can be finer tuned by modifying ${ALLUXIO_HOME}/conf/log4j.properties.

For example, if you want to change log level for the remote logger for Alluxio master logs, you can modify the corresponding appender’s threshold.

# Remote appender for Master
log4j.appender.REMOTE_MASTER_LOGGER=org.apache.log4j.net.SocketAppender
log4j.appender.REMOTE_MASTER_LOGGER.Port=${alluxio.logserver.port}
log4j.appender.REMOTE_MASTER_LOGGER.RemoteHost=${alluxio.logserver.hostname}
log4j.appender.REMOTE_MASTER_LOGGER.ReconnectionDelay=10000
log4j.appender.REMOTE_MASTER_LOGGER.filter.ID=alluxio.AlluxioRemoteLogFilter
log4j.appender.REMOTE_MASTER_LOGGER.filter.ID.ProcessType=MASTER
# Set the threshold to your desired log level
log4j.appender.REMOTE_MASTER_LOGGER.Threshold=WARN

This enables you to further customize the appender in log4j.properties to, for example, specify the log format. How to do that is beyond the scope of this documentation.

Configuring Applications Process

Logging can be configured to send log files to a remote server via a SocketAppender

Include a SocketAppender in the logging configuration by adding it to the log4j.properties file that the compute framework utilizes for logging.

An example configuration for a SocketAppender can be found below:

# Appender to send logs to a log server
log4j.appender.CLIENT_REMOTE_LOGGER=org.apache.log4j.net.SocketAppender
log4j.appender.CLIENT_REMOTE_LOGGER.Port=<PORT_OF_LOG_SERVER>
log4j.appender.CLIENT_REMOTE_LOGGER.RemoteHost=<HOSTNAME_OF_LOG_SERVER>
log4j.appender.CLIENT_REMOTE_LOGGER.ReconnectionDelay=10000
log4j.appender.CLIENT_REMOTE_LOGGER.layout=org.apache.log4j.PatternLayout
log4j.appender.CLIENT_REMOTE_LOGGER.layout.ConversionPattern=%d{ISO8601} %-5p %c{1} - %m%n

Enable the CLIENT_REMOTE_LOGGER appender by adding it to an existing logger within the a log4j configuration:

log4j.rootLogger=DEBUG, CLIENT_REMOTE_LOGGER

Again, refer to the documentation for the corresponding framework linked in the previous section to locate the log4j configuration file.