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Objective

Apache NiFi provides the option of starting an embedded ZooKeeper server. However, NiFi can also be configured to run with an external ZooKeeper server. This article describes how to install and configure a 3 host ZooKeeper ensemble to work with a 2 node NiFi cluster.

Environment

This tutorial was tested using the following environment and components:

  • Mac OS X 10.11.6
  • Apache ZooKeeper 3.4.6
  • Apache NiFi 1.3.0

ZooKeeper

ZooKeeper Version

The version of ZooKeeper chosen for this tutorial is Release 3.4.6.

Note: ZooKeeper 3.4.6 is the version supported by the latest and previous versions of Hortonworks HDF as shown in the "Component Availability In HDF" table of the HDF 3.0.1.1 Release Notes.

ZooKeeper Download

Go to http://www.apache.org/dyn/closer.cgi/zookeeper/ to determine the best Apache mirror site to download a stable ZooKeeper distribution. From that mirror site, select the zookeeper-3.4.6 directory and download the zookeeper-3.4.6.tar.gz file.

Unzip the tar.gz file and create 3 copies of the distribution directory, one for each host in the ZooKeeper ensemble. For example:

 /zookeeper-1
 /zookeeper-2
 /zookeeper-3

Note: In this tutorial, we are running multiple servers on the same machine.

ZooKeeper Configuration

"zoo.cfg" file

Next we need to create three config files. In the conf directory of zookeeper-1, create a zoo.cfg file with the following contents:

 tickTime=2000
 dataDir=/usr/local/zookeeper1
 clientPort=2181
 initLimit=5
 syncLimit=2
 server.1=localhost:2888:3888
 server.2=localhost:2889:3889
 server.3=localhost:2890:3890

Because we are running multiple ZooKeeper servers on a single machine, we specified the servername as localhost with unique quorum & leader election ports (i.e. 2888:3888, 2889:3889, 2890:3890) for each server.X.

Create similar zoo.cfg files in the conf directories of zookeeper-2 and zookeeper-3 with modified values for dataDir and clientPort properties as separate dataDirs and distinct clientPorts are necessary.

"myid" file

Every machine that is part of the ZooKeeper ensemble needs to know about every other machine in the ensemble. As such, we need to attribute a server id to each machine by creating a file named myid, one for each server, which resides in that server's data directory, as specified by the configuration file parameter dataDir.

For example, create a myid file in /usr/local/zookeeper1 that consists of a single line with the text "1" and nothing else. Create the other myid files in the /usr/local/zookeeper2 and /usr/local/zookeeper3 directories with the contents of "2" and "3" respectively.

Note: More information about ZooKeper configuration settings can be found in the ZooKeeper Getting Started Guide.

ZooKeeper Startup

Start up each ZooKeeper host, by navigating to the /bin directory of each and applying the following command:

 ./zkServer.sh start

NiFi

NiFi Configuration

For a two node NiFi cluster, in each conf directory modify the following properties in the nifi.properties file:

 nifi.state.management.embedded.zookeeper.start=false
 nifi.zookeeper.connect.string=localhost:2181,localhost:2182,localhost:2183

The first property configures NiFi to not use its embedded ZooKeeper. As a result, the zookeeper.properties and state-management.xml files in the conf directory are ignored. The second property must be specified to join the cluster as it lists all the ZooKeeper instances in the ensemble.

NiFi Startup

You can now start up each NiFi node. When the UI is available, create or upload a flow that has processors that capture state information. For example, import and setup the flow from the Change Data Capture (CDC) with Apache NiFi series:

34667-1-cdc-template.png

In addition to the other setup steps from the CDC article, since this environment is a cluster, for the CaptureChangeMySQL processor, go to the Scheduling tab on the Configure Processor dialog. Change the Execution setting to "Primary node" from "All nodes":

34668-2-primarynode.png

Run the flow and select "View State" from the CaptureChangeMySQL and/or EnforceOrder processors to verify that state information is managed properly by the external ZooKeeper ensemble:

34669-3-viewstate.png

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Comments

Hello,

I have a question if you can help answer that would be great.

Can we run Nifi in standalone mode (not cluster) in an Open Shift Pod but manage state in zookeeper to ensure if the openshift pod reboots the states of the stateful processors are not lost? it appears to me that NiFi architecture does not fit containerization.

Thoughts?

New Contributor

i am getting zookeeper already running on pid.  how to fix it?

Community Manager

@nifi_pista , as this is an older article, you would have a better chance of receiving a resolution by starting a new thread. This will also provide the opportunity to provide details specific to your environment that could aid others in providing a more accurate answer to your question. 

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‎08-17-2019 11:20 AM
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