syslog-ng Open Source Edition 3.22 - Administration Guide

Prerequisites

To send messages from syslog-ng OSE to HDFS, complete the following steps.

How syslog-ng OSE interacts with HDFS

The syslog-ng OSE application sends the log messages to the official HDFS client library, which forwards the data to the HDFS nodes. The way syslog-ng OSE interacts with HDFS is described in the following steps.

1. After syslog-ng OSE is started and the first message arrives to the hdfs destination, the hdfs destination tries to connect to the HDFS NameNode. If the connection fails, syslog-ng OSE will repeatedly attempt to connect again after the period set in time-reopen() expires.

2. syslog-ng OSE checks if the path to the logfile exists. If a directory does not exist syslog-ng OSE automatically creates it. syslog-ng OSE creates the destination file (using the filename set in the syslog-ng OSE configuration file, with a UUID suffix to make it unique, for example, /usr/hadoop/logfile.txt.3dc1c59e-ab3b-4b71-9e81-93db477ed9d9) and writes the message into the file. After the file is created, syslog-ng OSE will write all incoming messages into the hdfs destination.

   NOTE: When the hdfs-append-enabled() option is set to true, syslog-ng OSE will not assign a new UUID suffix to an existing file, because it is then possible to open a closed file and append data to that.

   NOTE: You cannot set when log messages are flushed. Hadoop performs this action automatically, depending on its configured block size, and the amount of data received. There is no way for the syslog-ng OSE application to influence when the messages are actually written to disk. This means that syslog-ng OSE cannot guarantee that a message sent to HDFS is actually written to disk. When using flow-control, syslog-ng OSE acknowledges a message as written to disk when it passes the message to the HDFS client. This method is as reliable as your HDFS environment.

3. If the HDFS client returns an error, syslog-ng OSE attempts to close the file, then opens a new file and repeats sending the message (trying to connect to HDFS and send the message), as set in the retries() parameter. If sending the message fails for retries() times, syslog-ng OSE drops the message.

4. The syslog-ng OSE application closes the destination file in the following cases:

   • syslog-ng OSE is reloaded

   • syslog-ng OSE is restarted

   • The HDFS client returns an error.

5. If the file is closed and you have set an archive directory, syslog-ng OSE moves the file to this directory. If syslog-ng OSE cannot move the file for some reason (for example, syslog-ng OSE cannot connect to the HDFS NameNode), the file remains at its original location, syslog-ng OSE will not try to move it again.

Storing messages with MapR-FS

The syslog-ng OSE application is also compatible with MapR File System (MapR-FS). MapR-FS provides better performance, reliability, efficiency, maintainability, and ease of use compared to the default Hadoop Distributed Files System (HDFS). To use MapR-FS with syslog-ng OSE, complete the following steps:

1. Install MapR libraries. Instead of the official Apache HDFS libraries, MapR uses different libraries. The supported version is MapR 4.x.

   1. Download the libraries from the Maven Repository and Artifacts for MapR or get it from an already existing MapR installation.

   2. Install MapR. If you do not know how to install MapR, follow the instructions on the MapR website.

2. In a default MapR installation, the required libraries are installed in the following path: /opt/mapr/lib.

   Enter the path where MapR was installed in the class-path option of the hdfs destination, for example:

   class-path("/opt/mapr/lib/")

   If the libraries were downloaded from the Maven Repository, the following additional libraries will be requiered. Note that the version numbers in the filenames can be different in the various Hadoop releases:commons-collections-3.2.1.jar, commons-logging-1.1.3.jar, hadoop-auth-2.5.1.jar, log4j-1.2.15.jar, slf4j-api-1.7.5.jar, commons-configuration-1.6.jar, guava-13.0.1.jar, hadoop-common-2.5.1.jar, maprfs-4.0.2-mapr.jar, slf4j-log4j12-1.7.5.jar, commons-lang-2.5.jar, hadoop-0.20.2-dev-core.jar, json-20080701.jar, protobuf-java-2.5.0.jar, zookeeper-3.4.5-mapr-1406.jar.

3. Configure the hdfs destination in syslog-ng OSE.

   Example: Storing logfiles with MapR-FS

   The following example defines an hdfs destination for MapR-FS using only the required parameters.

   @module mod-java
   @include "scl.conf"
   
   destination d_mapr {
       hdfs(
           client-lib-dir("/opt/syslog-ng/lib/syslog-ng/java-modules/:/opt/mapr/lib/")
           hdfs-uri("maprfs://10.140.32.80")
           hdfs-file("/user/log/logfile.txt")
       );
   };
   

Kerberos authentication with syslog-ng hdfs() destination

Version 3.10 and later supports Kerberos authentication to authenticate the connection to your Hadoop cluster. syslog-ng OSE assumes that you already have a Hadoop and Kerberos infrastructure.

destination d_hdfs {
    hdfs(client-lib-dir("/hdfs-libs/lib")
    hdfs-uri("hdfs://hdp-kerberos.syslog-ng.example:8020")
    kerberos-keytab-file("/opt/syslog-ng/etc/hdfs.headless.keytab")
    kerberos-principal("hdfs-hdpkerberos@MYREALM")
    hdfs-file("/var/hdfs/test.log"));
};