[HADOOP-11656] Classpath isolation for downstream clients

• Type: New Feature
• Status: Resolved
• Priority: Blocker
• Resolution: Done
• Fix Version/s: 3.0.0-beta1
• Labels: classloading classpath dependencies scripts shell
• Target Version/s: 3.0.0-beta1
• Assignee: Sean Busbey
• Reporter: Sean Busbey
• Created: 01/Mar/15 17:47
• Updated: 28/Oct/22 22:53
• Resolved: 27/Sep/17 18:25

Description

Currently, Hadoop exposes downstream clients to a variety of third party libraries. As our code base grows and matures we increase the set of libraries we rely on. At the same time, as our user base grows we increase the likelihood that some downstream project will run into a conflict while attempting to use a different version of some library we depend on. This has already happened with i.e. Guava several times for HBase, Accumulo, and Spark (and I'm sure others).

While YARN-286 and MAPREDUCE-1700 provided an initial effort, they default to off and they don't do anything to help dependency conflicts on the driver side or for folks talking to HDFS directly. This should serve as an umbrella for changes needed to do things thoroughly on the next major version.

We should ensure that downstream clients

1) can depend on a client artifact for each of HDFS, YARN, and MapReduce that doesn't pull in any third party dependencies

2) only see our public API classes (or as close to this as feasible) when executing user provided code, whether client side in a launcher/driver or on the cluster in a container or within MR.

This provides us with a double benefit: users get less grief when they want to run substantially ahead or behind the versions we need and the project is freer to change our own dependency versions because they'll no longer be in our compatibility promises.

Project specific task jiras to follow after I get some justifying use cases written in the comments.

Issue Links

• is related to: HADOOP-14089 Automated checking for malformed client artifacts.
• is related to: HADOOP-15137 ClassNotFoundException: org.apache.hadoop.yarn.server.api.DistributedSchedulingAMProtocol when using hadoop-client-minicluster
• is related to: HADOOP-14931 Isolation of native libraries in JARs
• is related to: HADOOP-15139 [Umbrella] Improvements and fixes for Hadoop shaded client work
• is related to: HADOOP-14771 hadoop-client does not include hadoop-yarn-client
• relates to: HADOOP-1815 Separate client and server jars
• relates to: HADOOP-10893 isolated classloader on the client side
• relates to: HADOOP-13070 classloading isolation improvements for stricter dependencies
• relates to: SPARK-40939 Release a shaded version of Apache Spark / shade jars on main jar
• relates to: HADOOP-13866 Upgrade netty-all to 4.1.1.Final
• relates to: HDFS-6200 Create a separate jar for hdfs-client
• links to: HADOOP-11656_proposal (rendered)