GeoMesa Kafka Quick Start

This tutorial is the fastest and easiest way to get started with GeoMesa using Kafka for streaming data. It is a good stepping-stone on the path to the other tutorials, that present increasingly involved examples of how to use GeoMesa.

About this Tutorial

In the spirit of keeping things simple, the code in this tutorial only does a few small things:

  1. Establishes a new (static) SimpleFeatureType
  2. Prepares the Kafka topic to write this type of data
  3. Creates a few thousand example SimpleFeatures
  4. Writes these SimpleFeatures to the Kafka topic
  5. Visualize the changing data in GeoServer (optional)
  6. Creates event listeners for SimpleFeature updates (optional)

The quick start operates by simultaneously querying and writing several thousand feature updates. The same feature identifier is used for each update, so there will only be a single “live” feature at any one time.

The data used is from New York City taxi activity data published by the University of Illinois. More information about the dataset is available here.

For this demo, only a single taxi is being tracked.

Background

Apache Kafka is “publish-subscribe messaging rethought as a distributed commit log.”

In the context of GeoMesa, Kafka is a useful tool for working with streams of geospatial data. Interaction with Kafka in GeoMesa occurs through the KafkaDataStore which implements the GeoTools DataStore interface.

Prerequisites

Before you begin, you must have the following installed and configured:

  • Java JDK 1.8
  • Apache Maven 3.5.2 or later
  • a GitHub client
  • a Kafka instance version 0.9.x or later

Ensure your Kafka and Zookeeper instances are running. You can use Kafka’s quickstart to get Kafka/Zookeeper instances up and running quickly.

Configure GeoServer (optional)

You can use GeoServer to access and visualize the data stored in GeoMesa. In order to use GeoServer, download and install version 2.12.x. Then follow the instructions in Installing GeoMesa Kafka in GeoServer to enable GeoMesa.

Download and Build the Tutorial

Pick a reasonable directory on your machine, and run:

$ git clone https://github.com/geomesa/geomesa-tutorials.git
$ cd geomesa-tutorials

Warning

Make sure that you download or checkout the version of the tutorials project that corresponds to your GeoMesa version. See About Tutorial Versions for more details.

To ensure that the quick start works with your environment, modify the pom.xml to set the appropriate versions for Kafka, Zookeeper, etc.

For ease of use, the project builds a bundled artifact that contains all the required dependencies in a single JAR. To build, run:

$ mvn clean install -pl geomesa-tutorials-kafka/geomesa-tutorials-kafka-quickstart -am

Running the Tutorial

On the command line, run:

$ java -cp geomesa-tutorials-kafka/geomesa-tutorials-kafka-quickstart/target/geomesa-tutorials-kafka-quickstart-$VERSION.jar \
    org.geomesa.example.kafka.KafkaQuickStart \
    --kafka.brokers <brokers>                 \
    --kafka.zookeepers <zookeepers>

where you provide the following arguments:

  • <brokers> your Kafka broker instances, comma separated. For a local install, this would be localhost:9092
  • <zookeepers> your Zookeeper nodes, comma separated. For a local install, this would be localhost:2181

Optionally, you can also specify that the quick start should delete its data upon completion. Use the --cleanup flag when you run to enable this behavior.

Once run, the quick start will create the Kafka topic, then pause and prompt you to register the layer in GeoServer. If you do not want to use GeoServer, you can skip this step. Otherwise, follow the instructions in the next section before returning here.

Once you continue, the tutorial should run for approximately thirty seconds. You should see the following output:

Loading datastore

Creating schema: taxiId:String,dtg:Date,geom:Point

Generating test data

Feature type created - register the layer 'tdrive-quickstart' in geoserver with bounds: MinX[116.22366] MinY[39.72925] MaxX[116.58804] MaxY[40.09298]
Press <enter> to continue

Writing features to Kafka... refresh GeoServer layer preview to see changes
Current consumer state:
1277=1277|2008-02-03T04:32:53.000Z|POINT (116.35 39.90003)
Current consumer state:
1277=1277|2008-02-03T17:58:49.000Z|POINT (116.38812 39.93196)
Current consumer state:
1277=1277|2008-02-04T06:46:26.000Z|POINT (116.40218 39.94439)
Current consumer state:
1277=1277|2008-02-04T19:55:45.000Z|POINT (116.3631 39.94646)
Current consumer state:
1277=1277|2008-02-05T09:39:48.000Z|POINT (116.58264 40.07556)
Current consumer state:
1277=1277|2008-02-05T22:24:50.000Z|POINT (116.34112 39.95363)
Current consumer state:
1277=1277|2008-02-06T14:17:29.000Z|POINT (116.54203 39.91476)
Current consumer state:
1277=1277|2008-02-07T02:53:55.000Z|POINT (116.35683 39.89809)
Current consumer state:
1277=1277|2008-02-07T15:48:47.000Z|POINT (116.36785 39.99471)
Current consumer state:
1277=1277|2008-02-08T04:20:19.000Z|POINT (116.42872 39.91531)
Current consumer state:
1277=1277|2008-02-08T17:14:15.000Z|POINT (116.34609 39.93924)

Done

Visualize Data With GeoServer (optional)

You can use GeoServer to access and visualize the data stored in GeoMesa. In order to use GeoServer, download and install version 2.12.x. Then follow the instructions in Installing GeoMesa Kafka in GeoServer to enable GeoMesa.

Register the GeoMesa Store with GeoServer

Log into GeoServer using your user and password credentials. Click “Stores” and “Add new Store”. Select the Kafka (GeoMesa) vector data source, and fill in the required parameters.

Basic store info:

  • workspace this is dependent upon your GeoServer installation
  • data source name pick a sensible name, such as geomesa_quick_start
  • description this is strictly decorative; GeoMesa quick start

Connection parameters:

  • these are the same parameter values that you supplied on the command line when you ran the tutorial; they describe how to connect to the Kafka instance where your data reside

Click “Save”, and GeoServer will search Zookeeper for any GeoMesa-managed feature types.

Publish the Layer

If you have already run the command to start the tutorial, then GeoServer should recognize the tdrive-quickstart feature type, and should present that as a layer that can be published. Click on the “Publish” link. If not, then run the tutorial as described above in Running the Tutorial. When the tutorial pauses, go to “Layers” and “Add new Layer”. Select the GeoMesa Kafka store you just created, and then click “publish” on the tdrive-quickstart layer.

You will be taken to the Edit Layer screen. You will need to enter values for the data bounding boxes. For this demo, use the values MinX: 116.22366, MinY: 39.72925, MaxX: 116.58804, MaxY: 40.09298.

Click on the “Save” button when you are done.

Take a Look

Click on the “Layer Preview” link in the left-hand gutter. If you don’t see the quick-start layer on the first page of results, enter the name of the layer you just created into the search box, and press <Enter>.

At first, there will be no data displayed. Once you have reached this point, return to the quick start console and hit “<enter>” to continue the tutorial. As the data is updated in Kafka, you can refresh the layer preview page to see the feature moving around.

What’s Happening in GeoServer

The layer preview of GeoServer uses the KafkaFeatureStore to show a real time view of the current state of the data stream. There is a single SimpleFeature being updated over time in Kafka which is reflected in the GeoServer display.

As you refresh the page, you should see the SimpleFeature move around. Due to the nature of the taxi’s routes, and the speed up of time in replaying the data, there isn’t much of a pattern to the movement.

Looking at the Code

The source code is meant to be accessible for this tutorial. The logic is contained in the generic org.geomesa.example.quickstart.GeoMesaQuickStart in the geomesa-quickstart-common module, and the Kafka-specific org.geomesa.example.kafka.KafkaQuickStart in the geomesa-quickstart-kafka module. Some relevant methods are:

  • createDataStore get a datastore instance from the input configuration
  • createSchema create the schema in the datastore, as a pre-requisite to writing data
  • writeFeatures overridden in the KafkaQuickStart to simultaneously write and read features from Kafka
  • queryFeatures not used in this tutorial
  • cleanup delete the sample data and dispose of the datastore instance

The quickstart uses a small subset of taxi data. Code for parsing the data into GeoTools SimpleFeatures is contained in org.geomesa.example.data.TDriveData:

  • getSimpleFeatureType creates the SimpleFeatureType representing the data
  • getTestData parses an embedded CSV file to create SimpleFeature objects
  • getTestQueries not used in this tutorial

Listening for Feature Events (optional)

The GeoTools API also includes a mechanism to fire off a FeatureEvent each time there is an event in a DataStore (typically when the data is changed). A client may implement a FeatureListener, which has a single method called changed() that is invoked as each FeatureEvent is fired.

The code in KafkaListener implements a simple FeatureListener that prints the messages received. Open up a second terminal window and run:

$ java -cp geomesa-tutorials-kafka/geomesa-tutorials-kafka-quickstart/target/geomesa-tutorials-kafka-quickstart-$VERSION.jar \
    org.geomesa.example.kafka.KafkaListener \
    --kafka.brokers <brokers>               \
    --kafka.zookeepers <zookeepers>

Use the same settings for <brokers> and <zookeepers> that you did previously. Then in the original terminal window, re-run the KafkaQuickStart code as before. The KafkaListener terminal should produce messages like the following:

Received FeatureEvent from schema 'tdrive-quickstart' of type 'CHANGED'
1277=1277|2008-02-02T13:34:51.000Z|POINT (116.32674 39.89577)

The KafkaListener code will run until interrupted (typically with ctrl-c).

The portion of KafkaListener that creates and implements the FeatureListener is:

FeatureListener listener = featureEvent -> {
    System.out.println("Received FeatureEvent from schema '" + typeName + "' of type '" + featureEvent.getType() + "'");
    if (featureEvent.getType() == FeatureEvent.Type.CHANGED &&
        featureEvent instanceof KafkaFeatureChanged) {
        System.out.println(DataUtilities.encodeFeature(((KafkaFeatureChanged) featureEvent).feature()));
    } else if (featureEvent.getType() == FeatureEvent.Type.REMOVED) {
        System.out.println("Received Delete for filter: " + featureEvent.getFilter());
    }
};
datastore.getFeatureSource(typeName).addFeatureListener(listener);

(note the use of a lambda expression to create the listener)