Cloudera Docs

Autoconfiguration

Cloudera Manager provides several interactive wizards to automate common workflows:
  • Add Service - used when adding a new service
  • Import MapReduce - used when migrating from MapReduce to YARN

In some of these wizards, Cloudera Manager uses a set of rules to automatically configure certain settings to best suit the characteristics of the deployment. For example, the number of hosts in the deployment drives the memory requirements for certain monitoring daemons: the more hosts, the more memory is needed. Additionally, wizards that are tasked with creating new roles will use a similar set of rules to determine an ideal host placement for those roles.

Scope

The following table shows, for each wizard, the scope of entities it affects during autoconfiguration and role-host placement.
Wizard Autoconfiguration Scope Role-Host Placement Scope
Import MapReduce Existing YARN service N/A

Certain autoconfiguration rules are unscoped, that is, they configure settings belonging to entities that aren't necessarily the entities under the wizard's scope. These exceptions are explicitly listed.

Autoconfiguration

Cloudera Manager employs several different rules to drive automatic configuration, with some variation from wizard to wizard. These rules range from the simple to the complex.

Configuration Scope

One of the points of complexity in autoconfiguration is configuration scope. The configuration hierarchy as it applies to services is as follows: configurations may be modified at the service level (affecting every role in the service), role group level (affecting every role instance in the group), or role level (affecting one role instance). A configuration found in a lower level takes precedence over a configuration found in a higher level.

With the exception of the Static Service Pools, and the Import MapReduce wizard, all Cloudera Manager wizards follow a basic pattern:
  1. Every role in scope is moved into its own, new, role group.
  2. This role group is the receptacle for the role's "idealized" configuration. Much of this configuration is driven by properties of the role's host, which can vary from role to role.
  3. Once autoconfiguration is complete, new role groups with common configurations are merged.
  4. The end result is a smaller set of role groups, each with an "idealized" configuration for some subset of the roles in scope. A subset can have any number of roles; perhaps all of them, perhaps just one, and so on.
The Static Service Pools and Import MapReduce wizards configure role groups directly and do not perform any merging.

Data Directories

Several autoconfiguration rules work with data directories, and there's a common sub-rule used by all such rules to determine, out of all the mountpoints present on a host, which are appropriate for data. The subrule works as follows:
  • The initial set of mountpoints for a host includes all those that are disk-backed. Network-backed mountpoints are excluded.
  • Mountpoints beginning with /boot, /cdrom, /usr, /tmp, /home, or /dev are excluded.
  • Mountpoints beginning with /media are excluded, unless the backing device's name contains /xvd somewhere in it.
  • Mountpoints beginning with /var are excluded, unless they are /var or /var/lib.
  • The largest mount point (in terms of total space, not available space) is determined.
  • Other mountpoints with less than 1% total space of the largest are excluded.
  • Mountpoints beginning with /var or equal to / are excluded unless they’re the largest mount point.
  • Remaining mountpoints are sorted lexicographically and retained for future use.

Memory

The rules used to autoconfigure memory reservations are perhaps the most complicated rules employed by Cloudera Manager. When configuring memory, Cloudera Manager must take into consideration which roles are likely to enjoy more memory, and must not over commit hosts if at all possible. To that end, it needs to consider each host as an entire unit, partitioning its available RAM into segments, one segment for each role. To make matters worse, some roles have more than one memory segment. For example, a Solr server has two memory segments: a JVM heap used for most memory allocation, and a JVM direct memory pool used for HDFS block caching. Here is the overall flow during memory autoconfiguration:
  1. The set of participants includes every host under scope as well as every {role, memory segment} pair on those hosts. Some roles are under scope while others are not.
  2. For each {role, segment} pair where the role is under scope, a rule is run to determine four different values for that pair:
    • Minimum memory configuration. Cloudera Manager must satisfy this minimum, possibly over-committing the host if necessary.
    • Minimum memory consumption. Like the above, but possibly scaled to account for inherent overhead. For example, JVM memory values are multiplied by 1.3 to arrive at their consumption value.
    • Ideal memory configuration. If RAM permits, Cloudera Manager will provide the pair with all of this memory.
    • Ideal memory consumption. Like the above, but scaled if necessary.
  3. For each {role, segment} pair where the role is not under scope, a rule is run to determine that pair's existing memory consumption. Cloudera Manager will not configure this segment but will take it into consideration by setting the pair's "minimum" and "ideal" to the memory consumption value.
  4. For each host, the following steps are taken:
    1. 20% of the host's available RAM is subtracted and reserved for the OS.
    2. sum(minimum_consumption) and sum(ideal_consumption) are calculated.
    3. An "availability ratio" is built by comparing the two sums against the host's available RAM.
      1. If RAM < sum(minimum) ratio = 0
      2. If RAM >= sum(ideal) ratio = 1
    4. If the host has more available memory than the total of the ideal memory for all roles assigned to the host, each role is assigned its ideal memory and autoconfiguration is finished.
    5. Cloudera Manager assigns all available host memory by setting each {role, segment} pair to the same consumption value, except in cases where that value is below the minimum memory or above the ideal memory for that pair. In that case, it is set to the minimum memory or the ideal memory as appropriate. This ensures that pairs with low ideal memory requirements are completely satisfied before pairs with higher ideal memory requirements.
  5. The {role, segment} pair is set with the value from the previous step. In the Static Service Pools wizard, the role group is set just once (as opposed to each role).
  6. Custom post-configuration rules are run.

Customization rules are applied in steps 2, 3 and 7. In step 2, there's a generic rule for most cases, as well as a series of custom rules for certain {role, segment} pairs. Likewise, there's a generic rule to calculate memory consumption in step 3 as well as some custom consumption functions for certain {role, segment} pairs.

Step 2 Generic Rule

For every {role, segment} pair where the segment defines a default value, the pair's minimum is set to the segment's minimum value (or 0 if undefined), and the ideal is set to the segment's default value.

Step 2 Custom Rules

HDFS

For the NameNode and Secondary NameNode JVM heaps, the minimum is 50 MB and the ideal is max(4 GB, sum_over_all(DataNode mountpoints’ available space) / 0.000008).

MapReduce

For the JobTracker JVM heap, the minimum is 50 MB and the ideal is max(1 GB, round((1 GB * 2.3717181092 * ln(number of TaskTrackers in MapReduce service)) - 2.6019933306)). If the number of TaskTrackers <= 5, the ideal is 1 GB.

For the mapper JVM heaps, the minimum is 1 and the ideal is the number of cores, including hyperthreads, on the TaskTracker host. Memory consumption is scaled by mapred_child_java_opts_max_heap (the size of a task's heap).

For the reducer JVM heaps, the minimum is 1 and the ideal is (number of cores, including hyperthreads, on the TaskTracker host) / 2. Memory consumption is scaled by mapred_child_java_opts_max_heap (the size of a task's heap).

HBase

For the memory total allowed for HBase RegionServer JVM heap, the minimum is 50 MB and the ideal is min (31 GB ,(total RAM on region server host) * 0.64)

YARN

For the memory total allowed for containers, the minimum is 1 GB and the ideal is (total RAM on NodeManager host) * 0.64.

Hue

With the exception of the Beeswax Server (only in CDH 4), Hue roles do not have memory limits. Therefore, Cloudera Manager treats them as roles that consume a fixed amount of memory by setting their minimum and ideal consumption values, but not their configuration values. The two consumption values are set to 256 MB.

Impala

With the exception of the Impala daemon, Impala roles do not have memory limits. Therefore, Cloudera Manager treats them as roles that consume a fixed amount of memory by setting their minimum/ideal consumption values, but not their configuration values. The two consumption values are set to 150 MB for the Catalog Server and 64 MB for the StateStore.

For the Impala Daemon memory limit, the minimum is 256 MB and the ideal is (total RAM on daemon host) * 0.64.

Solr

For the Solr Server JVM heap, the minimum is 50 MB and the ideal is min(64 GB, (total RAM on Solr Server host) * 0.64) / 2.6. For the Solr Server JVM direct memory segment, the minimum is 256 MB and the ideal is min(64 GB, (total RAM on Solr Server host) * 0.64) / 2.

Cloudera Management Service
  • Alert Publisher JVM heap - Treated as if it consumed a fixed amount of memory by setting the minimum/ideal consumption values, but not the configuration values. The two consumption values are set to 256 MB.
  • Service and Host Monitor JVM heaps - The minimum is 50 MB and the ideal is either 256 MB (10 or fewer managed hosts), 1 GB (100 or fewer managed hosts), or 2 GB (over 100 managed hosts).
  • Event Server, Reports Manager, and Navigator Audit Server JVM heaps - The minimum is 50 MB and the ideal is 1 GB.
  • Navigator Metadata Server JVM heap - The minimum is 512 MB and the ideal is 2 GB.
  • Service and Host Monitor off-heap memory segments - The minimum is either 768 MB (10 or fewer managed hosts), 2 GB (100 or fewer managed hosts), or 6 GB (over 100 managed hosts). The ideal is always twice the minimum.

Step 2 Generic Rule for Static Service Pools Wizard

For every {role, segment} pair where the segment defines a default value and an autoconfiguration share, the pair's minimum is set to the segment's default value, and the ideal is set to min((segment soft max (if exists) or segment max (if exists) or 2^63-1), (total RAM on role's host * 0.8 / segment scale factor * service percentage chosen in wizard * segment autoconfiguration share)).

Autoconfiguration shares are defined as follows:
  • HBase RegionServer JVM heap: 1
  • HDFS DataNode JVM heap: 1 in CDH 4, 0.2 in CDH 5
  • HDFS DataNode maximum locked memory: 0.8 (CDH 5 only)
  • Solr Server JVM heap: 0.5
  • Solr Server JVM direct memory: 0.5
  • Spark Standalone Worker JVM heap: 1
  • Accumulo Tablet Server JVM heap: 1
  • Add-on services: any

Roles not mentioned here do not define autoconfiguration shares and thus aren't affected by this rule.

Additionally, there's a generic rule to handle cgroup.memory_limit_in_bytes, which is unused by Cloudera services but is available for add-on services. Its behavior varies depending on whether the role in question has segments or not.

With Segments

The minimum is the min(cgroup.memory_limit_in_bytes_min (if exists) or 0, sum_over_all(segment minimum consumption)), and the ideal is the sum of all segment ideal consumptions.

Without Segments

The minimum is cgroup.memory_limit_in_bytes_min (if exists) or 0, and the ideal is (total RAM on role's host * 0.8 * service percentage chosen in wizard).

Step 3 Custom Rules for Static Service Pools Wizard

YARN

For the memory total allowed for containers, the minimum is 1 GB and the ideal is min(8 GB, (total RAM on NodeManager host) * 0.8 * service percentage chosen in wizard).

Impala

For the Impala Daemon memory limit, the minimum is 256 MB and the ideal is ((total RAM on Daemon host) * 0.8 * service percentage chosen in wizard).

MapReduce
  • Mapper JVM heaps - the minimum is 1 and the ideal is (number of cores, including hyperthreads, on the TaskTracker host * service percentage chosen in wizard). Memory consumption is scaled by mapred_child_java_opts_max_heap (the size of a given task's heap).
  • Reducer JVM heaps - the minimum is 1 and the ideal is (number of cores, including hyperthreads on the TaskTracker host * service percentage chosen in wizard) / 2. Memory consumption is scaled by mapred_child_java_opts_max_heap (the size of a given task's heap).

Step 3 Generic Rule

For every {role, segment} pair, the segment's current value is converted into bytes, and then multiplied by the scale factor (1.0 by default, 1.3 for JVM heaps, and freely defined for Custom Service Descriptor services).

Step 3 Custom Rules

Impala

For the Impala Daemon, the memory consumption is 0 if YARN Service for Resource Management is set. If the memory limit is defined but not -1, its value is used verbatim. If it's defined but -1, the consumption is equal to the total RAM on the Daemon host. If it is undefined, the consumption is (total RAM * 0.8).

Solr

For the Solr Server JVM direct memory segment, the consumption is equal to the value verbatim provided solr.hdfs.blockcache.enable and solr.hdfs.blockcache.direct.memory.allocation are both true. Otherwise, the consumption is 0.

Step 7 Custom Rules

HDFS
  • NameNode JVM heaps are equalized. For every pair of NameNodes in an HDFS service with different heap sizes, the larger heap size is reset to the smaller one.
  • JournalNode JVM heaps are equalized. For every pair of JournalNodes in an HDFS service with different heap sizes, the larger heap size is reset to the smaller one.
  • NameNode and Secondary NameNode JVM heaps are equalized. For every {NameNode, Secondary NameNode} pair in an HDFS service with different heap sizes, the larger heap size is reset to the smaller one.
HBase

Master JVM heaps are equalized. For every pair of Masters in an HBase service with different heap sizes, the larger heap size is reset to the smaller one.

Impala

If an Impala service has YARN Service for Resource Management set, every Impala Daemon memory limit is set to the value of (yarn.nodemanager.resource.memory-mb * 1 GB) if there's a YARN NodeManager co-located with the Impala Daemon.

MapReduce

JobTracker JVM heaps are equalized. For every pair of JobTrackers in an MapReduce service with different heap sizes, the larger heap size is reset to the smaller one.

Oozie

Oozie Server JVM heaps are equalized. For every pair of Oozie Servers in an Oozie service with different heap sizes, the larger heap size is reset to the smaller one.

YARN

ResourceManager JVM heaps are equalized. For every pair of ResourceManagers in a YARN service with different heap sizes, the larger heap size is reset to the smaller one.

ZooKeeper

ZooKeeper Server JVM heaps are equalized. For every pair of servers in a ZooKeeper service with different heap sizes, the larger heap size is reset to the smaller one.

General Rules

HBase

  • hbase.replication - For each HBase service, set to true if there's a Key-Value Store Indexer service in the cluster. This rule is unscoped; it can fire even if the HBase service is not under scope.
  • replication.replicationsource.implementation - For each HBase service, set to com.ngdata.sep.impl.SepReplicationSource if there's a Keystore Indexer service in the cluster. This rule is unscoped; it can fire even if the HBase service is not under scope.

HDFS

  • dfs.datanode.du.reserved - For each DataNode, set to min((total space of DataNode host largest mountpoint) / 10, 10 GB).
  • dfs.namenode.name.dir - For each NameNode, set to the first two mountpoints on the NameNode host with /dfs/nn appended.
  • dfs.namenode.checkpoint.dir - For each Secondary NameNode, set to the first mountpoint on the Secondary NameNode host with /dfs/snn appended.
  • dfs.datanode.data.dir - For each DataNode, set to all the mountpoints on the host with /dfs/dn appended.
  • dfs.journalnode.edits.dir - For each JournalNode, set to the first mountpoint on the JournalNode host with /dfs/jn appended.
  • dfs.datanode.failed.volumes.tolerated - For each DataNode, set to (number of mountpoints on DataNode host) / 2.
  • dfs.namenode.service.handler.count and dfs.namenode.handler.count - For each NameNode, set to ln(number of DataNodes in this HDFS service) * 20.
  • dfs.datanode.hdfs-blocks-metadata.enabled - For each HDFS service, set to true if there's an Impala service in the cluster. This rule is unscoped; it can fire even if the HDFS service is not under scope.
  • dfs.client.read.shortcircuit - For each HDFS service, set to true if there's an Impala service in the cluster. This rule is unscoped; it can fire even if the HDFS service is not under scope.
  • dfs.datanode.data.dir.perm - For each DataNode, set to 755 if there's an Impala service in the cluster and the cluster isn’t Kerberized. This rule is unscoped; it can fire even if the HDFS service is not under scope.
  • fs.trash.interval - For each HDFS service, set to 1.

Hue

  • WebHDFS dependency - For each Hue service, set to either the first HttpFS role in the cluster, or, if there are none, the first NameNode in the cluster.
  • HBase Thrift Server dependency- For each Hue service in a CDH 4.4 or higher cluster, set to the first HBase Thrift Server in the cluster.

Impala

For each Impala service, set Enable Audit Collection and Enable Lineage Collection to true if there's a Cloudera Management Service with a Navigator Audit Server and Navigator Metadata Server roles. This rule is unscoped; it can fire even if the Impala service is not under scope.

MapReduce

  • mapred.local.dir - For each JobTracker, set to the first mountpoint on the JobTracker host with /mapred/jt appended.
  • mapred.local.dir - For each TaskTracker, set to all the mountpoints on the host with /mapred/local appended.
  • mapred.reduce.tasks - For each MapReduce service, set to max(1, sum_over_all(TaskTracker number of reduce tasks (determined via mapred.tasktracker.reduce.tasks.maximum for that TaskTracker, which is configured separately)) / 2).
  • mapred.job.tracker.handler.count - For each JobTracker, set to max(10, ln(number of TaskTrackers in this MapReduce service) * 20).
  • mapred.submit.replication - If there's an HDFS service in the cluster, for each MapReduce service, set to max(min(number of DataNodes in the HDFS service, value of HDFS Replication Factor), sqrt(number of DataNodes in the HDFS service)).
  • mapred.tasktracker.instrumentation - If there's a management service, for each MapReduce service, set to org.apache.hadoop.mapred.TaskTrackerCmonInst. This rule is unscoped; it can fire even if the MapReduce service is not under scope.

YARN

  • yarn.nodemanager.local-dirs - For each NodeManager, set to all the mountpoints on the NodeManager host with /yarn/nm appended.
  • yarn.nodemanager.resource.cpu-vcores - For each NodeManager, set to the number of cores (including hyperthreads) on the NodeManager host.
  • mapred.reduce.tasks - For each YARN service, set to max(1,sum_over_all(NodeManager number of cores, including hyperthreads) / 2).
  • yarn.resourcemanager.nodemanagers.heartbeat-interval-ms - For each NodeManager, set to max(100, 10 * (number of NodeManagers in this YARN service)).
  • yarn.scheduler.maximum-allocation-vcores - For each ResourceManager, set to max_over_all(NodeManager number of vcores (determined via yarn.nodemanager.resource.cpu-vcores for that NodeManager, which is configured separately)).
  • yarn.scheduler.maximum-allocation-mb - For each ResourceManager, set to max_over_all(NodeManager amount of RAM (determined via yarn.nodemanager.resource.memory-mb for that NodeManager, which is configured separately)).
  • mapreduce.client.submit.file.replication - If there's an HDFS service in the cluster, for each YARN service, set to max(min(number of DataNodes in the HDFS service, value of HDFS Replication Factor), sqrt(number of DataNodes in the HDFS service)).

All Services

If a service dependency is unset, and a service with the desired type exists in the cluster, set the service dependency to the first such target service. Applies to all service dependencies except YARN Service for Resource Management. Applies only to the Installation and Add Cluster wizards.

Role-Host Placement

Cloudera Manager employs the same role-host placement rule regardless of wizard. The set of hosts considered depends on the scope. If the scope is a cluster, all hosts in the cluster are included. If a service, all hosts in the service's cluster are included. If the Cloudera Management Service, all hosts in the deployment are included. The rules are as follows:
  1. The hosts are sorted from most to least physical RAM. Ties are broken by sorting on hostname (ascending) followed by host identifier (ascending).
  2. The overall number of hosts is used to determine which arrangement to use. These arrangements are hard-coded, each dictating for a given "master" role type, what index (or indexes) into the sorted host list in step 1 to use.
  3. Master role types are included based on several factors:
    • Is this role type part of the service (or services) under scope?
    • Does the service already have the right number of instances of this role type?
    • Does the cluster's CDH version support this role type?
    • Does the installed license allow for this role type to exist?
  4. Master roles are placed on each host using the indexes and the sorted host list. If a host already has a given master role, it is skipped.
  5. An HDFS DataNode is placed on every host outside of the arrangement described in step 2, provided HDFS is one of the services under scope.
  6. Certain "worker" roles are placed on every host where an HDFS DataNode exists, either because it existed there prior to the wizard, or because it was added in the previous step. The supported worker role types are:
    • MapReduce TaskTrackers
    • YARN NodeManagers
    • HBase RegionServers
    • Impala Daemons
    • Spark Workers
  7. Hive gateways are placed on every host, provided a Hive service is under scope and a gateway didn’t already exist on a given host.
  8. Spark on YARN gateways are placed on every host, provided a Spark on YARN service is under scope and a gateway didn’t already exist on a given host.
This rule merely dictates the default placement of roles; you are free to modify it before it is applied by the wizard.