As part of a project for my day job, I've been getting to grips with Flume. Chances are that if you've found this post, you're already aware of what Flume does, but for the uninitiated:
Flume is a distributed, reliable, and available service for efficiently collecting, aggregating, and moving large amounts of log data. Its main goal is to deliver data from applications to Hadoop’s HDFS. It has a simple and flexible architecture based on streaming data flows. It is robust and fault tolerant with tunable reliability mechanisms and many failover and recovery mechanisms. The system is centrally managed and allows for intelligent dynamic management. It uses a simple extensible data model that allows for online analytic applications.
The work that I'm doing requires me to manipulate events as they traverse a data flow. To do this I will extend Flume using its plugin functionality and a custom Decorator:
Sink decorators can add properties to the sink and can modify the data streams that pass through them. For example, you can use them to increase reliability via write ahead logging, increase network throughput via batching/compression, sampling, benchmarking, and even lightweight analytics.
Flume ships with source code for some sample plugins called HelloWorld and HBaseSink. I planned to use the Decorator component of the HelloWorld plugin as the basis for my work, but following the instructions for installing the example plugins in the Flume User Guide presented some problems:
- The rpm packages provided by Cloudera do not include the sample plugin source code
- The instructions in the Flume User Guide use ant, which require 'build.xml'. The plugin source only includes 'pom.xml'.
Not having used Java in anger for some time, I had to bring myself up to speed and work through a few issues to get up and running.
As background, here's how to install Flume 0.9.4 from rpms on a java-less RHEL 5.3 server:
- Download and install the latest Java SE rpm.bin from Oracle, available here.
Setup the new Java binary as default using alternatives:
>alternatives --install /usr/bin/java java /usr/java/jdk1.6.0_30/jre/bin/java 1000 >alternatives --config java
Setup Java environment variables in \~/.bash_profile, (logout/in for this to take effect):
# Java export JAVA_HOME=/usr/java/jdk1.6.0_30/ export PATH=$PATH:$JAVA_HOME/bin:$PATH
Check that the default java is correct:
>java -version java version "1.6.0_30" Java(TM) SE Runtime Environment (build 1.6.0_30-b12) Java HotSpot(TM) 64-Bit Server VM (build 20.5-b03, mixed mode)
- Install Flume using yum
If you've done all of this correctly, you should have a working flume installation:
>flume version Flume 0.9.4-cdh3u3 Git repository https://github.com/cloudera/flume/flume-core rev unknown Compiled by jenkins on 20120126-1114
This procedure is the same for all machines that will be part of your Flume installation, be they agent, collector or master. You will now be able to work through the examples in the User Guide.
Installing Apache Maven
Now, to set up an environment for building the example plugins. The user guide instructs us to use Apache Ant to build these, but at some stage the Flume dev team have dropped Ant in favour of Apache Maven. Whereas Ant uses a build.xml file to define a project, Maven uses pom.xml.
So before we can build the plugins, we need to install Maven:
Download and unpack Maven:
>elinks http://www.apache.org/dyn/closer.cgi/maven/binaries/apache-maven-3.0.4-bin.zip >unzip apache-maven-3.0.4-bin.zip >cd /usr/local/ >mv ~/apache-maven-3.0.4 ./ >chmod 755 apache-maven-3.0.4/
Setup Maven environment variables in \~/.bash_profile, (logout/in for this to take effect):
# Maven export M2_HOME=/usr/apache-maven-3.0.4 export M2=$M2_HOME/bin export PATH=$M2:$PATH
Check that Maven is set up correctly:
>mvn --version Apache Maven 3.0.4 (r1232337; 2012-01-17 19:44:56+1100) Maven home: /usr/apache-maven-3.0.4 Java version: 1.6.0_30, vendor: Sun Microsystems Inc. Java home: /usr/java/jdk1.6.0_30/jre Default locale: en_US, platform encoding: UTF-8 OS name: "linux", version: "2.6.18-128.el5", arch: "amd64", family: "unix"
Build Example Plugin
With Flume and Maven installed, we can finally build an example plugin. These aren't included in the rpm install, so we download the Flume tar.gz and build the plugin from the source code within.
For this example we build the HelloWorld plugin:
Download the flume tar.gz:
>elinks http://archive.cloudera.com/cdh/3/flume-0.9.4-cdh3u3.tar.gz >tar -xzvf flume-0.9.4-cdh3u3.tar.gz
Use maven to build the plugin as a jar file:
>cd flume-0.9.4-cdh3u3/plugins/flume-plugin-helloworld >mvn install
Install Example Plugin
Now we install and configure the newly-built plugin:
Copy the .jar that we just created to your Flume library, (look at the output of the mvn command to check where the .jar was dumped). It's possible to set a Flume environment variable pointing at the location of your plugins, but this way is simpler:
>cp /root/.m2/repository/com/cloudera/flume/plugin/flume-plugin-helloworld/0.9.4-cdh3u3/flume-plugin-helloworld-0.9.4-cdh3u3.jar /usr/lib/flume/lib/
Each Flume node is configured by the file flume-site.xml. The rpm ships with a template, which we rename to use:
>cd /usr/lib/flume/conf >mv flume-site.xml.template flume-site.xml
Edit/uncomment the plugin property in flume-site.xml so that it contains at least the following:
<configuration> <property> <name>flume.plugin.classes</name> <value>helloworld.HelloWorldSink,helloworld.HelloWorldSource,helloworld.HelloWorldDecorator</value> <description>Comma separated list of plugins</description> </property> </configuration>
Finally we're ready to roll. Start flume with
The following output confirms that the plugin is loading correctly:
2012-03-15 17:11:37,268 [main] INFO conf.SourceFactoryImpl: Found source builder helloWorldSource in helloworld.HelloWorldSource 2012-03-15 17:11:37,329 [main] INFO conf.SinkFactoryImpl: Found sink builder helloWorldSink in helloworld.HelloWorldSink 2012-03-15 17:11:37,330 [main] INFO conf.SinkFactoryImpl: Found sink decorator helloWorldDecorator in helloworld.HelloWorldDecorator
You'll need to scp the .jar file to all other machines that will use the plugin, (agents, collectors and masters) and repeat the steps above.
To confirm that the plugin is loaded correctly on the master, go to http://\<master_server>:35871/masterext.jsp. You should see the HelloWorld Source, Sink and Decorator listed.
That's it! You can now configure your Flume streams using the HellowWorld plugins. Next I'll post how I modified these example plugins to create the much-requested Flume filtering decorator.