druid/docs/content/Indexing-Service.md

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The indexing service is a highly-available, distributed service that runs indexing related tasks. Indexing service tasks create (and sometimes destroy) Druid segments. The indexing service has a master/slave like architecture.

The indexing service is composed of three main components: a peon component that can run a single task, a middle manager component that manages peons, and an overlord component that manages task distribution to middle managers. Overlords and middle managers may run on the same node or across multiple nodes while middle managers and peons always run on the same node.

Quick Start

Run:

io.druid.cli.Main server overlord

With the following JVM configuration:

-server
-Xmx2g
-Duser.timezone=UTC
-Dfile.encoding=UTF-8

-Ddruid.host=localhost
-Ddruid.port=8080
-Ddruid.service=overlord

-Ddruid.zk.service.host=localhost

-Ddruid.db.connector.connectURI=jdbc:mysql://localhost:3306/druid
-Ddruid.db.connector.user=druid
-Ddruid.db.connector.password=diurd

-Ddruid.selectors.indexing.serviceName=overlord
-Ddruid.indexer.runner.javaOpts="-server -Xmx1g"
-Ddruid.indexer.runner.startPort=8081
-Ddruid.indexer.fork.property.druid.computation.buffer.size=268435456

You can now submit simple indexing tasks to the indexing service.

Indexing Service Overview

Overlord Node

The overlord node is responsible for accepting tasks, coordinating task distribution, creating locks around tasks, and returning statuses to callers.

Usage

Tasks are submitted to the overlord node in the form of JSON objects. Tasks can be submitted via POST requests to:

http://<OVERLORD_IP>:<port>/druid/indexer/v1/task

Tasks can cancelled via POST requests to:

http://<OVERLORD_IP>:<port>/druid/indexer/v1/task/{taskId}/shutdown

Issuing the cancel request will kill –9 the task.

Task statuses can be retrieved via GET requests to:

http://<OVERLORD_IP>:<port>/druid/indexer/v1/task/{taskId}/status

Task segments can be retrieved via GET requests to:

http://<OVERLORD_IP>:<port>/druid/indexer/v1/task/{taskId}/segments

Console

The overlord console can be used to view pending tasks, running tasks, available workers, and recent worker creation and termination. The console can be accessed at:

http://<OVERLORD_IP>:8080/console.html

Autoscaling

The Autoscaling mechanisms currently in place are tightly coupled with our deployment infrastructure but the framework should be in place for other implementations. We are highly open to new implementations or extensions of the existing mechanisms. In our own deployments, middle manager nodes are Amazon AWS EC2 nodes and they are provisioned to register themselves in a galaxy environment.

If autoscaling is enabled, new middle managers may be added when a task has been in pending state for too long. Middle managers may be terminated if they have not run any tasks for a period of time.

JVM Configuration

In addition to the configuration of some of the default modules in Configuration, the overlord module requires the following basic configs to run in remote mode:

Property	Description	Default
druid.indexer.runner.type	Choices "local" or "remote". Indicates whether tasks should be run locally or in a distributed environment.	local
druid.indexer.storage.type	Choices are "local" or "db". Indicates whether incoming tasks should be stored locally (in heap) or in a database. Storing incoming tasks in a database allows for tasks to be bootstrapped if the overlord should fail.	local

The following configs only apply if the overlord is running in remote mode:

Property	Description	Default
druid.indexer.runner.taskAssignmentTimeout	How long to wait after a task as been assigned to a middle manager before throwing an error.	PT5M
druid.indexer.runner.minWorkerVersion	The minimum middle manager version to send tasks to.	none
druid.indexer.runner.compressZnodes	Indicates whether or not the overlord should expect middle managers to compress Znodes.	false
druid.indexer.runner.maxZnodeBytes	The maximum size Znode in bytes that can be created in Zookeeper.	524288

There are additional configs for autoscaling (if it is enabled):

Property	Description	Default
druid.indexer.autoscale.doAutoscale	If set to "true" autoscaling will be enabled.	false
druid.indexer.autoscale.provisionPeriod	How often to check whether or not new middle managers should be added.	PT1M
druid.indexer.autoscale.terminatePeriod	How often to check when middle managers should be removed.	PT1H
druid.indexer.autoscale.originTime	The starting reference timestamp that the terminate period increments upon.	2012-01-01T00:55:00.000Z
druid.indexer.autoscale.strategy	Choices are "noop" or "ec2". Sets the strategy to run when autoscaling is required.	noop
druid.indexer.autoscale.workerIdleTimeout	How long can a worker be idle (not a run task) before it can be considered for termination.	PT10M
druid.indexer.autoscale.maxScalingDuration	How long the overlord will wait around for a middle manager to show up before giving up.	PT15M
druid.indexer.autoscale.numEventsToTrack	The number of autoscaling related events (node creation and termination) to track.	10
druid.indexer.autoscale.pendingTaskTimeout	How long a task can be in "pending" state before the overlord tries to scale up.	PT30S
druid.indexer.autoscale.workerVersion	If set, will only create nodes of set version during autoscaling. Overrides dynamic configuration.	null
druid.indexer.autoscale.workerPort	The port that middle managers will run on.	8080

Dynamic Configuration

Overlord dynamic configuration is mainly for autoscaling. The overlord reads a worker setup spec as a JSON object from the Druid MySQL config table. This object contains information about the version of middle managers to create, the maximum and minimum number of middle managers in the cluster at one time, and additional information required to automatically create middle managers.

The JSON object can be submitted to the overlord via a POST request at:

http://<COORDINATOR_IP>:<port>/druid/indexer/v1/worker/setup

A sample worker setup spec is shown below:

{
  "minVersion":"some_version",
  "minNumWorkers":"0",
  "maxNumWorkers":"10",
  "nodeData": {
    "type":"ec2",
    "amiId":"ami-someId",
    "instanceType":"m1.xlarge",
    "minInstances":"1",
    "maxInstances":"1",
    "securityGroupIds":["securityGroupIds"],
    "keyName":"keyName"
  },
  "userData":{
    "classType":"galaxy",
    "env":"druid",
    "version":"druid_version",
    "type":"sample_cluster/worker"
  }
}

Issuing a GET request at the same URL will return the current worker setup spec that is currently in place. The worker setup spec list above is just a sample and it is possible to extend the code base for other deployment environments. A description of the worker setup spec is shown below.

Property	Description	Default
minVersion	The coordinator only assigns tasks to workers with a version greater than the minVersion. If this is not specified, the minVersion will be the same as the coordinator version.	none
minNumWorkers	The minimum number of workers that can be in the cluster at any given time.	0
maxNumWorkers	The maximum number of workers that can be in the cluster at any given time.	0
nodeData	A JSON object that contains metadata about new nodes to create.	none
userData	A JSON object that contains metadata about how the node should register itself on startup. This data is sent with node creation requests.	none

Running

io.druid.cli.Main server overlord

Note: When running the overlord in local mode, all middle manager and peon configurations must be provided as well.

MiddleManager Node

The middle manager node is a worker node that executes submitted tasks. Middle Managers forward tasks to peons that run in separate JVMs. Each peon is capable of running only one task at a time, however, a middle manager may have multiple peons.

JVM Configuration

Middle managers pass their configurations down to their child peons. The middle manager module requires the following configs:

Property	Description	Default
druid.worker.ip	The IP of the worker.	localhost
druid.worker.version	Version identifier for the middle manager.	0
druid.worker.capacity	Maximum number of tasks the middle manager can accept.	Number of available processors - 1
druid.indexer.runner.compressZnodes	Indicates whether or not the middle managers should compress Znodes.	false
druid.indexer.runner.maxZnodeBytes	The maximum size Znode in bytes that can be created in Zookeeper.	524288
druid.indexer.runner.taskDir	Temporary intermediate directory used during task execution.	/tmp/persistent
druid.indexer.runner.javaCommand	Command required to execute java.	java
druid.indexer.runner.javaOpts	-X Java options to run the peon in its own JVM.	""
druid.indexer.runner.classpath	Java classpath for the peon.	System.getProperty("java.class.path")
druid.indexer.runner.startPort	The port that peons begin running on.	8080
druid.indexer.runner.allowedPrefixes	Whitelist of prefixes for configs that can be passed down to child peons.	"com.metamx", "druid", "io.druid", "user.timezone","file.encoding"

Running

io.druid.cli.Main server middleManager

Peons

Peons run a single task in a single JVM. Peons are a part of middle managers and should rarely (if ever) be run on their own.

JVM Configuration

Although peons inherit the configurations of their parent middle managers, explicit child peon configs can be set by prefixing them with:

druid.indexer.fork.property

Additional peon configs include:

Property	Description	Default
druid.peon.mode	Choices are "local" and "remote". Setting this to local means you intend to run the peon as a standalone node (Not recommended).	remote
druid.indexer.task.baseDir	Base temporary working directory.	/tmp
druid.indexer.task.baseTaskDir	Base temporary working directory for tasks.	/tmp/persistent/tasks
druid.indexer.task.hadoopWorkingPath	Temporary working directory for Hadoop tasks.	/tmp/druid-indexing
druid.indexer.task.defaultRowFlushBoundary	Highest row count before persisting to disk. Used for indexing generating tasks.	50000
druid.indexer.task.chathandler.type	Choices are "noop" and "announce". Certain tasks will use service discovery to announce an HTTP endpoint that events can be posted to.	noop

If the peon is running in remote mode, there must be an overlord up and running. Running peons in remote mode require the following configurations:

Property	Description	Default
druid.peon.taskActionClient.retry.minWait	The minimum retry time to communicate with overlord.	PT1M
druid.peon.taskActionClient.retry.maxWait	The maximum retry time to communicate with overlord.	PT10M
druid.peon.taskActionClient.retry.maxRetryCount	The maximum number of retries to communicate with overlord.	10

Running

The peon should very rarely ever be run independent of the middle manager.

io.druid.cli.Main internal peon <task_file> <status_file>

The task file contains the task JSON object. The status file indicates where the task status will be output.

Tasks

See Tasks.