Apache Hadoop
An Apache Hadoop container image. This image is meant to be used for creating a standalone cluster with multiple DataNodes.
Custom commands
This image contains a script named start-hadoop
(included in the PATH). This script is used to initialize NamaNodes and DataNodes.
HDFS user
The custom commands require an HDFS user to be set. The user's name if read from the HDFS_USER
environment variable and the user is automatically created by the commands.
Starting a NameNode
To start a NameNode run the following command:
start-hadoop namenode
The script supports running as a daemon if the daemon
argument is passed as the last argument. This is useful when another command must be used or when the image is being used as the base for another image. To run a NameNode as a daemon use the following command:
start-hadoop namenode daemon
Starting a DataNode
To start a DataNode run the following command:
start-hadoop datanode [NameNode]
The script supports running as a daemon if the daemon
argument is passed as the last argument. This is useful when another command must be used or when the image is being used as the base for another image. To run a NameNode as a daemon use the following command:
start-hadoop datanode [NameNode] daemon
Creating a cluster with Docker Compose
The easiest way to create a standalone cluster with this image is by using Docker Compose. The following snippet can be used as a docker-compose.yml
for a simple cluster:
version: "2"
services:
namenode:
image: singularities/hadoop
command: start-hadoop namenode
hostname: namenode
environment:
HDFS_USER: hdfsuser
ports:
- "8020:8020"
- "14000:14000"
- "50070:50070"
- "50075:50075"
- "10020:10020"
- "13562:13562"
- "19888:19888"
datanode:
image: singularities/hadoop
command: start-hadoop datanode namenode
environment:
HDFS_USER: hdfsuser
links:
- namenode
Persistence
The image has a volume mounted at /opt/hdfs
. To maintain states between restarts, mount a volume at this location. This should be done for the NameNode and the DataNodes.
Scaling
If you wish to increase the number of DataNodes scale the datanode
service by running the scale
command like follows:
docker-compose scale datanode=2
The DataNodes will automatically register themselves with the NameNode.