Working with different versions of Hadoop may require a bit of extra work for the time being. We will make changes to support different Hadoop versions in the near future. If you have problems outside of these instructions, please feel free to contact us in IRC or on the [forum](https://groups.google.com/forum/#!forum/druid-development).
Working with Hadoop 2.x
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The default version of Hadoop bundled with Druid is 2.3. This should work out of the box.
To override the default Hadoop version, both the Hadoop Index Task and the standalone Hadoop indexer support the parameter `hadoopDependencyCoordinates`. You can pass another set of Hadoop coordinates through this parameter (e.g. You can specify coordinates for Hadoop 2.4.0 as `["org.apache.hadoop:hadoop-client:2.4.0"]`).
The Hadoop Index Task takes this parameter has part of the task JSON and the standalone Hadoop indexer takes this parameter as a command line argument.
If you are still having problems, include all relevant hadoop jars at the beginning of the classpath of your indexing or historical nodes.
Members of the community have reported dependency conflicts between the version of Jackson used in CDH and Druid. Currently, our best workaround is to edit Druid's pom.xml dependencies to match the version of Jackson in your hadoop version and recompile Druid.
For more about building Druid, please see [Building Druid](../development/build.html).
Another workaround solution is to build a custom fat jar of Druid using [sbt](http://www.scala-sbt.org/), which manually excludes all the conflicting Jackson dependencies, and then put this fat jar in the classpath of the command that starts overlord indexing service. To do this, please follow the following steps.
(1) Download and install sbt.
(2) Make a new directory named 'druid_build'.
(3) Cd to 'druid_build' and create the build.sbt file with the content [here](./use_sbt_to_build_fat_jar.md).
You can always add more building targets or remove the ones you don't need.
(4) In the same directory creat a new directory named 'project'.
(5) Put the druid source code into 'druid_build/project'.
(6) Create a file 'druid_build/project/assembly.sbt' with content as follows.
(7) In the 'druid_build' directory, run 'sbt assembly'.
(8) In the 'druid_build/target/scala-2.10' folder, you will find the fat jar you just build.
(9) Make sure the jars you've uploaded has been completely removed. The hdfs directory is by default '/tmp/druid-indexing/classpath'.
(10) Include the fat jar in the classpath when you start the indexing service. Make sure you've removed 'lib/*' from your classpath because now the fat jar includes all you need.
We recommend recompiling Druid with your particular version of Hadoop by changing the dependencies in Druid's pom.xml files. Make sure to also either override the default `hadoopDependencyCoordinates` in the code or pass your Hadoop version in as part of indexing.
