Configuring Hadoop in Non-Secure Mode
Hadoop’s Java 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 : - etc/hadoop/core-site.xml,
etc/hadoop/hdfs-site.xml, etc/hadoop/yarn-site.xml and
etc/hadoop/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 etc/hadoop/hadoop-env.sh and
etc/hadoop/yarn-env.sh.
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.
HDFS daemons are NameNode,
SecondaryNameNode, and DataNode. YARN daemons are ResourceManager, NodeManager,
and WebAppProxy. If MapReduce is to be used, then the MapReduce Job History
Server will also be running. For large installations, these are generally
running on separate hosts.
Configuring Environment of Hadoop Daemons
Administrators
should use the etc/hadoop/hadoop-env.sh and optionally the etc/hadoop/mapred-env.sh and etc/hadoop/yarn-env.sh scripts
to do site-specific customization of the Hadoop daemons’ process environment.
|
Daemon |
Environment
Variable |
|
NameNode |
HDFS_NAMENODE_OPTS |
|
DataNode |
HDFS_DATANODE_OPTS |
|
Secondary NameNode |
HDFS_SECONDARYNAMENODE_OPTS |
|
ResourceManager |
YARN_RESOURCEMANAGER_OPTS |
|
NodeManager |
YARN_NODEMANAGER_OPTS |
|
WebAppProxy |
YARN_PROXYSERVER_OPTS |
|
Map Reduce Job History Server |
MAPRED_HISTORYSERVER_OPTS |
At
the very least, you must specify the JAVA_HOME so that it is
correctly defined on each remote node.
Administrators
can configure individual daemons using the configuration options shown below in
the table:
For
example, To configure Namenode to use parallelGC and a 8GB Java Heap, the
following statement should be added in hadoop-env.sh :
export HDFS_NAMENODE_OPTS="-XX:+UseParallelGC -Xmx8g"
See etc/hadoop/hadoop-env.sh for
other examples.
Other
useful configuration parameters that you can customize include:
HADOOP_PID_DIR -
The directory where the daemons’ process id files are stored.
HADOOP_LOG_DIR -
The directory where the daemons’ log files are stored. Log files are
automatically created if they don’t exist.
HADOOP_HEAPSIZE_MAX -
The maximum amount of memory to use for the Java heapsize. Units supported by
the JVM are also supported here. If no unit is present, it will be assumed the
number is in megabytes. By default, Hadoop will let the JVM determine how much
to use. This value can be overriden on a per-daemon basis using the
appropriate _OPTS variable listed above. For example, setting HADOOP_HEAPSIZE_MAX=1g and HADOOP_NAMENODE_OPTS="-Xmx5g" will
configure the NameNode with 5GB heap.
In
most cases, you should specify the HADOOP_PID_DIR and HADOOP_LOG_DIR directories
such that they 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.
It is also traditional to configure HADOOP_HOME in
the system-wide shell environment configuration. For example, a simple script
inside /etc/profile.d:
HADOOP_HOME=/path/to/hadoop
export HADOOP_HOME
Configuring the Hadoop Daemons
This section deals with important
parameters to be specified in the given configuration files:
etc/hadoop/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. |
etc/hadoop/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.hosts / dfs.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. |
etc/hadoop/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. Use a fully qualified class name,
e.g., org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.FairScheduler. |
|
|
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 |
|
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.hosts / dfs.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. |
etc/hadoop/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. Use a fully qualified class name,
e.g., org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.FairScheduler. |
|
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:
|
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. |
|
yarn.nodemanager.env-whitelist |
Environment
properties to be inherited by containers from NodeManagers |
For
mapreduce application in addition to the default values HADOOP_MAPRED_HOME
should to be added. Property value should
JAVA_HOME,HADOOP_COMMON_HOME,HADOOP_HDFS_HOME,HADOOP_CONF_DIR,CLASSPATH_PREPEND_DISTCACHE,HADOOP_YARN_HOME,HADOOP_MAPRED_HOME |
- 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. |
etc/hadoop/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. |
Monitoring
Health of NodeManagers
Hadoop
provides a mechanism by which administrators can configure the NodeManager to
run an administrator supplied script periodically to determine if a node is
healthy or not.
Administrators can determine if the node is in a
healthy state by performing any checks of their choice in the script. If the
script detects the node to be in an unhealthy state, it must print a line to
standard output beginning with the string ERROR. The NodeManager spawns the
script periodically and checks its output. If the script’s output contains the
string ERROR, as described above, the node’s status is reported as unhealthy and
the node is black-listed by the ResourceManager. No further tasks will be
assigned to this node. However, the NodeManager continues to run the script, so
that if the node becomes healthy again, it will be removed from the blacklisted
nodes on the ResourceManager automatically. The node’s health along with the
output of the script, if it is unhealthy, is available to the administrator in
the ResourceManager web interface. The time since the node was healthy is also
displayed on the web interface.
The
following parameters can be used to control the node health monitoring script
in etc/hadoop/yarn-site.xml.
|
Parameter |
Value |
Notes |
|
yarn.nodemanager.health-checker.script.path |
Node health script |
Script to check for node’s health
status. |
|
yarn.nodemanager.health-checker.script.opts |
Node health script options |
Options for script to check for node’s
health status. |
|
yarn.nodemanager.health-checker.interval-ms |
Node health script interval |
Time interval for running health
script. |
|
yarn.nodemanager.health-checker.script.timeout-ms |
Node health script timeout interval |
Timeout for health script execution. |
The health checker script is not supposed to give
ERROR if only some of the local disks become bad. NodeManager has the ability
to periodically check the health of the local disks (specifically checks
nodemanager-local-dirs and nodemanager-log-dirs) and after reaching the
threshold of number of bad directories based on the value set for the config
property yarn.nodemanager.disk-health-checker.min-healthy-disks, the whole node
is marked unhealthy and this info is sent to resource manager also. The boot
disk is either raided or a failure in the boot disk is identified by the health
checker script.
Slaves
File
List all worker hostnames or IP addresses in
your etc/hadoop/workers file, one per line. Helper scripts (described
below) will use the etc/hadoop/workers file to run commands on many
hosts at once. It is not used for any of the Java-based Hadoop configuration.
In order to use this functionality, ssh trusts (via either passphraseless ssh
or some other means, such as Kerberos) must be established for the accounts
used to run Hadoop.
Hadoop Rack Awareness
Many Hadoop components are rack-aware and take
advantage of the network topology for performance and safety. Hadoop daemons
obtain the rack information of the workers in the cluster by invoking an
administrator configured module. See the Rack Awareness documentation
for more specific information.
It is highly recommended configuring rack
awareness prior to starting HDFS.
Logging
Hadoop uses the Apache log4j via the Apache Commons
Logging framework for logging. Edit the etc/hadoop/log4j.properties file
to customize the Hadoop daemons’ logging configuration (log-formats and so on).
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