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Configuring Alluxio with HDFS

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This guide describes the instructions to configure HDFS as Alluxio’s under storage system.

Initial Setup

To run an Alluxio cluster on a set of machines, you must deploy Alluxio server binaries to each of these machines. You can either download the precompiled binaries directly with the correct Hadoop version (recommended), or compile the binaries from Alluxio source code (for advanced users).

Note that, when building Alluxio from source code, by default Alluxio server binaries is built to work with Apache Hadoop HDFS of version 2.2.0. To work with Hadoop distributions of other versions, one needs to specify the correct Hadoop profile and run the following in your Alluxio directory:

mvn install -P<YOUR_HADOOP_PROFILE> -DskipTests

Alluxio provides predefined build profiles including hadoop-1, hadoop-2.2, hadoop-2.3 … hadoop-2.8 for different distributions of Hadoop. If you want to build Alluxio with a specific Hadoop release version, you can also specify the version <YOUR_HADOOP_VERSION> in the command. For example,

mvn install -Phadoop-2.7 -Dhadoop.version=2.7.1 -DskipTests

would compile Alluxio for the Apache Hadoop version 2.7.1. Please visit the Building Alluxio Master Branch page for more information about support for other distributions.

If everything succeeds, you should see alluxio-assembly-server-1.5.0-jar-with-dependencies.jar created in the assembly/server/target directory and this is the jar file you can use to run both Alluxio Master and Worker.

Configuring Alluxio

You need to configure Alluxio to use under storage systems by modifying conf/alluxio-site.properties. If it does not exist, create the configuration file from the template.

cp conf/alluxio-site.properties.template conf/alluxio-site.properties

Basic Configuration

Edit conf/alluxio-site.properties file to set the under storage address to the HDFS namenode address and the HDFS directory you want to mount to Alluxio. For example, the under storage address can be hdfs://localhost:9000 if you are running the HDFS namenode locally with default port and mapping HDFS root directory to Alluxio, or hdfs://localhost:9000/alluxio/data if only the HDFS directory /alluxio/data is mapped to Alluxio.

alluxio.underfs.address=hdfs://NAMENODE:PORT

HDFS namenode HA mode

If HDFS namenodes are running in HA mode, both Alluxio servers and clients should be configured properly in order to access HDFS.

For Alluxio servers (masters and workers), copy or make symbolic links from hdfs-site.xml and core-site.xml from your hadoop installation into ${ALLUXIO_HOME}/conf. Alternatively, you can set alluxio.underfs.hdfs.configuration to the hadoop property file hdfs-site.xml (or core-site.xml) in conf/alluxio-site.properties (make sure all the relative configurations are available in the file).

Then, set the under storage address to hdfs://nameservice/ (nameservice is the name of HDFS service already configured in core-site.xml) if you are mapping HDFS root directory to Alluxio, or hdfs://nameservice/alluxio/data if only the HDFS directory /alluxio/data is mapped to Alluxio.

alluxio.underfs.address=hdfs://nameservice/

Next, for Alluxio clients, alluxio.underfs.hdfs.configuration should also be set to the hadoop property file hdfs-site.xml (or core-site.xml).

Ensure Correct Permission Mapping

Since v1.3, Alluxio supports filesystem user and permission checking by default. To ensure that the permission information of files/directories including user, group and mode in HDFS is consistent with Alluxio, the user to start Alluxio master and worker processes is required to be either case:

  1. HDFS super user. Namely, use the same user that starts HDFS namenode process to also start Alluxio master and worker processes.

  2. A member of HDFS superuser group. Edit HDFS configuration file hdfs-site.xml and check the value of configuration property dfs.permissions.superusergroup. If this property is set with a group (e.g., “hdfs”), add the user to start Alluxio process (e.g., “alluxio”) to this group (“hdfs”); if this property is not set, add a group to this property where your Alluxio running user is a member of this newly added group.

Note that, the user set above is only the identity that starts Alluxio master and worker processes. Once Alluxio servers started, it is unnecessary to run your Alluxio client applications using this user.

Running Alluxio Locally with HDFS

Before this step, please make sure your HDFS cluster is running and the directory mapped to Alluxio exists. After everything is configured, you can start up Alluxio locally to see that everything works.

bin/alluxio format
bin/alluxio-start.sh local

This should start one Alluxio master and one Alluxio worker locally. You can see the master UI at http://localhost:19999.

Next, you can run a simple example program:

bin/alluxio runTests

After this succeeds, you can visit HDFS web UI at http://localhost:50070 to verify the files and directories created by Alluxio exist. For this test, you should see files named like: /default_tests_files/BasicFile_STORE_SYNC_PERSIST

You can stop Alluxio any time by running:

bin/alluxio-stop.sh local