Cluster Installation and Configuration

Installation

Installing a Hadoop cluster typically involves unpacking the software on all the machines in the cluster or installing RPMs.

Typically one machine in the cluster is designated as the NameNode and another machine the as ResourceManager, exclusively. These are the masters.

The rest of the machines in the cluster act as both DataNode and NodeManager. These are the slaves.

Configuration

Hadoop 2 configuration is driven by two types of important configuration files:

• Read-only default configuration – core-default.xml, hdfs-default.xml, yarn-default.xml and mapred-default.xml.
• Site-specific configuration – conf/core-site.xml, conf/hdfs-site.xml, conf/yarn-site.xml and conf/mapred-site.xml.

Additionally, you can control the Hadoop scripts found in the bin/ directory of the distribution, by setting site-specific values via the conf/hadoop-env.sh and yarn-env.sh.

Site Configuration – To configure the Hadoop cluster you will need to configure the environment in which the Hadoop daemons execute as well as the configuration parameters for the Hadoop daemons. The Hadoop daemons are NameNode/DataNode and ResourceManager/NodeManager.

Configuring Environment – Administrators should use the conf/hadoop-env.sh and conf/yarn-env.sh script to do site-specific customization of the Hadoop daemons’ process environment. At the very least you should specify the JAVA_HOME so that it is correctly defined on each remote node. In most cases you should also specify HADOOP_PID_DIR and HADOOP_SECURE_DN_PID_DIR to point to directories that can only be written to by the users that are going to run the hadoop daemons. Otherwise there is the potential for a symlink attack.

Administrators can configure individual daemons using the configuration options shown below in the table:

Daemon	Environment Variable
NameNode	HADOOP_NAMENODE_OPTS
DataNode	HADOOP_DATANODE_OPTS
Secondary NameNode	HADOOP_SECONDARYNAMENODE_OPTS
ResourceManager	YARN_RESOURCEMANAGER_OPTS
NodeManager	YARN_NODEMANAGER_OPTS
WebAppProxy	YARN_PROXYSERVER_OPTS
Map Reduce Job History Server	HADOOP_JOB_HISTORYSERVER_OPTS

For example, To configure Namenode to use parallelGC, the following statement should be added in hadoop-env.sh :

export HADOOP_NAMENODE_OPTS=”-XX:+UseParallelGC ${HADOOP_NAMENODE_OPTS}”

Other useful configuration parameters that you can customize include:

• HADOOP_LOG_DIR / YARN_LOG_DIR – The directory where the daemons’ log files are stored. They are automatically created if they don’t exist.
• HADOOP_HEAPSIZE / YARN_HEAPSIZE – The maximum amount of heapsize to use, in MB e.g. if the variable is set to 1000 the heap will be set to 1000MB. This is used to configure the heap size for the daemon. By default, the value is 1000. If you want to configure the values separately for each daemon you can use.

Daemon	Environment Variable
ResourceManager	YARN_RESOURCEMANAGER_HEAPSIZE
NodeManager	YARN_NODEMANAGER_HEAPSIZE
WebAppProxy	YARN_PROXYSERVER_HEAPSIZE
Map Reduce Job History Server	HADOOP_JOB_HISTORYSERVER_HEAPSIZE

conf/core-site.xml

Parameter	Value	Notes
fs.defaultFS	NameNode URI	hdfs://host:port/
io.file.buffer.size	131072	Size of read/write buffer used in SequenceFiles.

conf/hdfs-site.xml

Configurations for NameNode:

Parameter	Value	Notes
dfs.namenode.name.dir	Path on the local filesystem where the NameNode stores the namespace and transactions logs persistently.	If this is a comma-delimited list of directories then the name table is replicated in all of the directories, for redundancy.
dfs.namenode.hosts / dfs.namenode.hosts.exclude	List of permitted/excluded DataNodes.	If necessary, use these files to control the list of allowable datanodes.
dfs.blocksize	268435456	HDFS blocksize of 256MB for large file-systems.
dfs.namenode.handler.count	100	More NameNode server threads to handle RPCs from large number of DataNodes.

Configurations for DataNode:

Parameter	Value	Notes
dfs.datanode.data.dir	Comma separated list of paths on the local filesystem of a DataNode where it should store its blocks.	If this is a comma-delimited list of directories, then data will be stored in all named directories, typically on different devices.

conf/yarn-site.xml

Configurations for ResourceManager and NodeManager:

Parameter	Value	Notes
yarn.acl.enable	true / false	Enable ACLs? Defaults to false.
yarn.admin.acl	Admin ACL	ACL to set admins on the cluster. ACLs are of for comma-separated-usersspacecomma-separated-groups. Defaults to special value of * which means anyone. Special value of just space means no one has access.
yarn.log-aggregation-enable	false	Configuration to enable or disable log aggregation

Configurations for ResourceManager:

Parameter	Value	Notes
yarn.resourcemanager.address	ResourceManager host:port for clients to submit jobs.	host:port If set, overrides the hostname set in yarn.resourcemanager.hostname.
yarn.resourcemanager.scheduler.address	ResourceManager host:port for ApplicationMasters to talk to Scheduler to obtain resources.	host:port If set, overrides the hostname set in yarn.resourcemanager.hostname.
yarn.resourcemanager.resource-tracker.address	ResourceManager host:port for NodeManagers.	host:port If set, overrides the hostname set in yarn.resourcemanager.hostname.
yarn.resourcemanager.admin.address	ResourceManager host:port for administrative commands.	host:port If set, overrides the hostname set in yarn.resourcemanager.hostname.
yarn.resourcemanager.webapp.address	ResourceManager web-ui host:port.	host:port If set, overrides the hostname set in yarn.resourcemanager.hostname.
yarn.resourcemanager.hostname	ResourceManager host.	host Single hostname that can be set in place of setting all yarn.resourcemanager*address resources. Results in default ports for ResourceManager components.
yarn.resourcemanager.scheduler.class	ResourceManager Scheduler class.	CapacityScheduler (recommended), FairScheduler (also recommended), or FifoScheduler
yarn.scheduler.minimum-allocation-mb	Minimum limit of memory to allocate to each container request at the Resource Manager.	In MBs
yarn.scheduler.maximum-allocation-mb	Maximum limit of memory to allocate to each container request at the Resource Manager.	In MBs
yarn.resourcemanager.nodes.include-path / yarn.resourcemanager.nodes.exclude-path	List of permitted/excluded NodeManagers.	If necessary, use these files to control the list of allowable NodeManagers.

Configurations for NodeManager:

Parameter	Value	Notes
yarn.nodemanager.resource.memory-mb	Resource i.e. available physical memory, in MB, for given NodeManager	Defines total available resources on the NodeManager to be made available to running containers
yarn.nodemanager.vmem-pmem-ratio	Maximum ratio by which virtual memory usage of tasks may exceed physical memory	The virtual memory usage of each task may exceed its physical memory limit by this ratio. The total amount of virtual memory used by tasks on the NodeManager may exceed its physical memory usage by this ratio.
yarn.nodemanager.local-dirs	Comma-separated list of paths on the local filesystem where intermediate data is written.	Multiple paths help spread disk i/o.
yarn.nodemanager.log-dirs	Comma-separated list of paths on the local filesystem where logs are written.	Multiple paths help spread disk i/o.
yarn.nodemanager.log.retain-seconds	10800	Default time (in seconds) to retain log files on the NodeManager Only applicable if log-aggregation is disabled.
yarn.nodemanager.remote-app-log-dir	/logs	HDFS directory where the application logs are moved on application completion. Need to set appropriate permissions. Only applicable if log-aggregation is enabled.
yarn.nodemanager.remote-app-log-dir-suffix	logs	Suffix appended to the remote log dir. Logs will be aggregated to ${yarn.nodemanager.remote-app-log-dir}/${user}/${thisParam} Only applicable if log-aggregation is enabled.
yarn.nodemanager.aux-services	mapreduce_shuffle	Shuffle service that needs to be set for Map Reduce applications.

Configurations for History Server (Needs to be moved elsewhere):

Parameter	Value	Notes
yarn.log-aggregation.retain-seconds	-1	How long to keep aggregation logs before deleting them. -1 disables. Be careful, set this too small and you will spam the name node.
yarn.log-aggregation.retain-check-interval-seconds	-1	Time between checks for aggregated log retention. If set to 0 or a negative value then the value is computed as one-tenth of the aggregated log retention time. Be careful, set this too small and you will spam the name node.

conf/mapred-site.xml

Configurations for MapReduce Applications:

Parameter	Value	Notes
mapreduce.framework.name	yarn	Execution framework set to Hadoop YARN.
mapreduce.map.memory.mb	1536	Larger resource limit for maps.
mapreduce.map.java.opts	-Xmx1024M	Larger heap-size for child jvms of maps.
mapreduce.reduce.memory.mb	3072	Larger resource limit for reduces.
mapreduce.reduce.java.opts	-Xmx2560M	Larger heap-size for child jvms of reduces.
mapreduce.task.io.sort.mb	512	Higher memory-limit while sorting data for efficiency.
mapreduce.task.io.sort.factor	100	More streams merged at once while sorting files.
mapreduce.reduce.shuffle.parallelcopies	50	Higher number of parallel copies run by reduces to fetch outputs from very large number of maps.

Configurations for MapReduce JobHistory Server:

Parameter	Value	Notes
mapreduce.jobhistory.address	MapReduce JobHistory Server host:port	Default port is 10020.
mapreduce.jobhistory.webapp.address	MapReduce JobHistory Server Web UI host:port	Default port is 19888.
mapreduce.jobhistory.intermediate-done-dir	/mr-history/tmp	Directory where history files are written by MapReduce jobs.
mapreduce.jobhistory.done-dir	/mr-history/done	Directory where history files are managed by the MR JobHistory Server.