Is it 50030 or 50300 for that JobTracker UI? I can never remember!
Hadoop’s daemons expose a handful of ports over TCP. Some of these ports are used by Hadoop’s daemons to communicate amongst themselves (to schedule jobs, replicate blocks, etc.). Others ports are listening directly to users, either via an interposed Java client, which communicates via internal protocols, or via plain old HTTP.
This post summarizes the ports that Hadoop uses; it’s intended to be a quick reference guide both for users, who struggle with remembering the correct port number, and systems administrators, who need to configure firewalls accordingly.
Web UIs for the Common User
The default Hadoop ports are as follows:
|❋ Replaces secondarynamenode in 0.21.
Hadoop daemons expose some information over HTTP. All Hadoop daemons expose the following:
- Exposes, for downloading, log files in the Java system property hadoop.log.dir.
- Allows you to dial up or down log4j logging levels. This is similar to hadoop daemonlog on the command line.
- Stack traces for all threads. Useful for debugging.
- Metrics for the server. Use /metrics?format=json to retrieve the data in a structured form. Available in 0.21.
Individual daemons expose extra daemon-specific endpoints as well. Note that these are not necessarily part of Hadoop’s public API, so they tend to change over time.
The Namenode exposes:
- Shows information about the namenode as well as the HDFS. There’s a link from here to browse the filesystem, as well.
- Shows lists of nodes that are disconnected from (DEAD) or connected to (LIVE) the namenode.
- Runs the “fsck” command. Not recommended on a busy cluster.
- Returns an XML-formatted directory listing. This is useful if you wish (for example) to poll HDFS to see if a file exists. The URL can include a path (e.g., /listPaths/user/philip) and can take optional GET arguments: /listPaths?recursive=yes will return all files on the file system; /listPaths/user/philip?filter=s.* will return all files in the home directory that start with s; and /listPaths/user/philip?exclude=.txt will return all files except text files in the home directory. Beware that filter and exclude operate on the directory listed in the URL, and they ignore the recursive flag.
- /data and /fileChecksum
- These forward your HTTP request to an appropriate datanode, which in turn returns the data or the checksum.
Datanodes expose the following:
- /browseBlock.jsp, /browseDirectory.jsp, tail.jsp, /streamFile, /getFileChecksum
- These are the endpoints that the namenode redirects to when you are browsing filesystem content. You probably wouldn’t use these directly, but this is what’s going on underneath.
- Every datanode verifies its blocks at configurable intervals. This endpoint provides a listing of that check.
The secondarynamenode exposes a simple status page with information including which namenode it’s talking to, when the last checkpoint was, how big it was, and which directories it’s using.
The jobtracker’s UI is commonly used to look at running jobs, and, especially, to find the causes of failed jobs. The UI is best browsed starting at /jobtracker.jsp. There are over a dozen related pages providing details on tasks, history, scheduling queues, jobs, etc.
Tasktrackers have a simple page (/tasktracker.jsp), which shows running tasks. They also expose /taskLog?taskid=<id> to query logs for a specific task. They use /mapOutput to serve the output of map tasks to reducers, but this is an internal API.
Under the Covers for the Developer and the System Administrator
Internally, Hadoop mostly uses Hadoop IPC to communicate amongst servers. (Part of the goal of the Apache Avro project is to replace Hadoop IPC with something that is easier to evolve and more language-agnostic; HADOOP-6170 is the relevant ticket.) Hadoop also uses HTTP (for the secondarynamenode communicating with the namenode and for the tasktrackers serving map outputs to the reducers) and a raw network socket protocol (for datanodes copying around data).
The following table presents the ports and protocols (including the relevant Java class) that Hadoop uses. This table does not include the HTTP ports mentioned above.
||Filesystem metadata operations.
||Custom Hadoop Xceiver: DataNode and DFSClient
||DFS data transfer
||IPC: InterDatanodeProtocol, ClientDatanodeProtocol
|Block metadata operations and recovery
||Same as namenode
||HDFS Metadata Operations
||IPC: JobSubmissionProtocol, InterTrackerProtocol
||Job submission, task tracker heartbeats.
||Communicating with child jobs
|✾ This is the port part of hdfs://host:8020/.
❖ Default is not well-defined. Common values are 8021, 9001, or 8012. See MAPREDUCE-566.
¤ Binds to an unused local port.
That’s quite a few ports! I hope this quick overview has been helpful.
Reference from http://www.cloudera.com/blog/2009/08/hadoop-default-ports-quick-reference/