Here is a Hadoop ports using reference, and hadoop services mapping
|DataNode HTTP UI||50075|
|NameNode HTTP UI||50070|
|backup /checkpoint node||50105|
|NameNode HTTPS UI||50470|
|HDFS over HTTP (HTTPFS)||14000|
|Hadoop MapReduce||JobHistory HTTP UI||19888|
|Hadoop YARN||App Masters||random|
|NodeManager HTTP UI||8042|
|ResourceManager HTTP UI||8088|
|Oozie Server Admin Port||11001|
|Oozie Server HTTP interface||11000|
|Spark Local Client Driver HTTP UI||4040 and up, random|
|Spark Yarn Shuffle Service||7337|
|Zookeeper||2181 (client port)|
A bit more brief introduction for ports from cloudera
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= 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.
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).