title: Walkthrough

Improvements from S4 0.5.0 include a more convenient configuration system, illustrated here: all platform and application parameters are specified when configuring/deploying the app.

Install S4

There are 2 ways:

We recommend getting the “source” release and building it

  • or checkout from the Apache git repository, by following the instructions. The 0.6.0 tag corresponds to the current release.

If you get the binary release, s4 scripts are immediately available. Otherwise you must build the project:

  • Compile and install S4 in the local maven repository: (you can also let the tests run without the -DskipTests option)

      S4:incubator-s4$ ./gradlew install -DskipTests
  .... verbose logs ...

  • Build the startup scripts:

      S4:incubator-s4$ ./gradlew s4-tools:installApp
  .... verbose logs 
  ...:s4-tools:installApp

Start a new application

S4 provides some scripts in order to simplify development and testing of applications. Let's see how to create a new project and start a sample application.

Create a new project

  • Create a new application template (here, we create it in the /tmp directory):

      S4:incubator-s4$ ./s4 newApp myApp -parentDir=/tmp
  ... some instructions on how to start ...

  • This creates a sample application in the specified directory, with the following structure:

      build.gradle  --> the template build file, that you'll need to customize
  gradlew --> references the gradlew script from the S4 installation
  s4 --> references the s4 script from the S4 installation, and adds an "adapter" task
  src/ --> sources (maven-like structure)

Have a look at the sample project content

The src/main/java/hello directory contains 3 files:

  • HelloPE.java : a very simple PE that simply prints the name contained in incoming events

#!java	

// ProcessingElement provides integration with the S4 platform
public class HelloPE extends ProcessingElement {

	// you should define downstream streams here and inject them in the app definition
	
	// PEs can maintain some state
	boolean seen = false;
	
	// This method is called upon a new Event on an incoming stream.
	// You may overload it for handling instances of your own specialized subclasses of Event
	public void onEvent(Event event) {
	    System.out.println("Hello " + (seen ? "again " : "") + event.get("name") + "!");
	    seen = true;
	}
    // skipped remaining methods
  • HelloApp.java: defines a simple application: exposes an input stream (“names”), connected to the HelloPE. See the event dispatch configuration page for more information about how events are dispatched.

#!java

// App parent class provides integration with the S4 platform
public class HelloApp extends App {
		
	@Override
	protected void onStart() {
	}
	
	@Override
	protected void onInit() {
	    // That's where we define PEs and streams
	    // create a prototype
	    HelloPE helloPE = createPE(HelloPE.class);
	    // Create a stream that listens to the "lines" stream and passes events to the helloPE instance.
	    createInputStream("names", new KeyFinder<Event>() {
	            // the KeyFinder is used to identify keys
	        @Override
	        public List<String> get(Event event) {
	            return Arrays.asList(new String[] { event.get("name") });
	        }
	    }, helloPE);
	}
// skipped remaining methods
  • HelloInputAdapter is a simple adapter that reads character lines from a socket, converts them into events, and sends the events to interested S4 apps, through the “names” stream

Run the sample app

In order to run an S4 application, you need :

  • to set-up a cluster: provision a cluster and start S4 nodes for that cluster
  • to package the app
  • to publish the app on the cluster

Set-up the cluster:

  • In 2 steps:

    1. Start a Zookeeper server instance (-clean option removes previous ZooKeeper data, if any):

       S4:incubator-s4$ ./s4 zkServer - clean
 S4:myApp$ calling referenced s4 script : /Users/S4/tmp/incubator-s4/s4
 [main] INFO  org.apache.s4.tools.ZKServer - Starting zookeeper server on port [2181]
 [main] INFO  org.apache.s4.tools.ZKServer - cleaning existing data in [/var/folders/8V/8VdgKWU3HCiy2yV4dzFpDk+++TI/-Tmp-/tmp/zookeeper/data] and [/var/folders/8V/8VdgKWU3HCiy2yV4dzFpDk+++TI/-Tmp-/tmp/zookeeper/log]

  1. Define a new cluster. Say a cluster named “cluster1” with 2 partitions, nodes listening to ports starting from 12000:

     S4:myApp$ ./s4 newCluster -c=cluster1 -nbTasks=2 -flp=12000
 calling referenced s4 script : /Users/S4/tmp/incubator-s4/s4
 [main] INFO  org.apache.s4.tools.DefineCluster - preparing new cluster [cluster1] with [2] node(s)
 [main] INFO  org.apache.s4.tools.DefineCluster - New cluster configuration uploaded into zookeeper
  • Alternatively you may combine these two steps into a single one, by passing the cluster configuration inline with the zkServer command:
#!bash
			
S4:incubator-s4$ ./s4 zkServer -clusters=c=cluster1:flp=12000:nbTasks=2 -clean
  • Start 2 S4 nodes with the default configuration, and attach them to cluster “cluster1” :
#!bash

S4:myApp$ ./s4 node -c=cluster1
calling referenced s4 script : /Users/S4/tmp/incubator-s4/s4
15:50:18.996 [main] INFO  org.apache.s4.core.Main - Initializing S4 node with :
- comm module class [org.apache.s4.comm.DefaultCommModule]
- comm configuration file [default.s4.comm.properties from classpath]
- core module class [org.apache.s4.core.DefaultCoreModule]
- core configuration file[default.s4.core.properties from classpath]
-extra modules: []
[main] INFO  org.apache.s4.core.Main - Starting S4 node.

This node will automatically download applications published for the cluster it belongs to and again (maybe in another shell):

S4:myApp$ ./s4 node -c=cluster1

  • Build, package and publish the app to cluster1:

    • This is done in 2 separate steps:

      1. Create an s4r archive. The following creates an archive named myApp.s4r (here you may specify an arbitrary name) in build/libs. Again specifying the app class is optional :

         ./s4 s4r -a=hello.HelloApp -b=`pwd`/build.gradle myApp

      2. Publish the s4r archive (you may first copy it to a more adequate place). The name of the app is arbitrary:

         ./s4 deploy -s4r=`pwd`/build/libs/myApp.s4r -c=cluster1 -appName=myApp

  • S4 nodes will detect the new application, download it, load it and start it. You will get something like:

      [ZkClient-EventThread-15-localhost:2181] INFO  o.a.s.d.DistributedDeploymentManager - Detected new application(s) to deploy {}[myApp]
  [ZkClient-EventThread-15-localhost:2181] INFO  org.apache.s4.core.Server - Local app deployment: using s4r file name [myApp] as application name
  [ZkClient-EventThread-15-localhost:2181] INFO  org.apache.s4.core.Server - App class name is: hello.HelloApp
  [ZkClient-EventThread-15-localhost:2181] INFO  o.a.s4.comm.topology.ClusterFromZK - Changing cluster topology to { nbNodes=0,name=unknown,mode=unicast,type=,nodes=[]} from null
  [ZkClient-EventThread-15-localhost:2181] INFO  o.a.s4.comm.topology.ClusterFromZK - Adding topology change listener:org.apache.s4.comm.tcp.TCPEmitter@79b2591c
  [ZkClient-EventThread-15-localhost:2181] INFO  o.a.s.comm.topology.AssignmentFromZK - New session:87684175268872203; state is : SyncConnected
  [ZkClient-EventThread-19-localhost:2181] INFO  o.a.s4.comm.topology.ClusterFromZK - Changing cluster topology to { nbNodes=1,name=cluster1,mode=unicast,type=,nodes=[{partition=0,port=12000,machineName=myMachine.myNetwork,taskId=Task-0}]} from { nbNodes=0,name=unknown,mode=unicast,type=,nodes=[]}
  [ZkClient-EventThread-15-localhost:2181] INFO  o.a.s.comm.topology.AssignmentFromZK - Successfully acquired task:Task-1 by myMachine.myNetwork
  [ZkClient-EventThread-19-localhost:2181] INFO  o.a.s4.comm.topology.ClusterFromZK - Changing cluster topology to { nbNodes=2,name=cluster1,mode=unicast,type=,nodes=[{partition=0,port=12000,machineName=myMachine.myNetwork,taskId=Task-0}, {partition=1,port=12001,machineName=myMachine.myNetwork,taskId=Task-1}]} from { nbNodes=1,name=cluster1,mode=unicast,type=,nodes=[{partition=0,port=12000,machineName=myMachine.myNetwork,taskId=Task-0}]}
  [ZkClient-EventThread-15-localhost:2181] INFO  o.a.s4.comm.topology.ClustersFromZK - New session:87684175268872205
  [ZkClient-EventThread-15-localhost:2181] INFO  o.a.s4.comm.topology.ClustersFromZK - Detected new stream [names]
  [ZkClient-EventThread-15-localhost:2181] INFO  o.a.s4.comm.topology.ClustersFromZK - New session:87684175268872206
  [ZkClient-EventThread-15-localhost:2181] INFO  o.a.s4.comm.topology.ClusterFromZK - Changing cluster topology to { nbNodes=2,name=cluster1,mode=unicast,type=,nodes=[{partition=0,port=12000,machineName=myMachine.myNetwork,taskId=Task-0}, {partition=1,port=12001,machineName=myMachine.myNetwork,taskId=Task-1}]} from null
  [ZkClient-EventThread-15-localhost:2181] INFO  org.apache.s4.core.Server - Loaded application from file /tmp/deploy-test/cluster1/myApp.s4r
  [ZkClient-EventThread-15-localhost:2181] INFO  o.a.s.d.DistributedDeploymentManager - Successfully installed application myApp
  [ZkClient-EventThread-15-localhost:2181] DEBUG o.a.s.c.g.OverloadDispatcherGenerator - Dumping generated overload dispatcher class for PE of class [class hello.HelloPE]
  [ZkClient-EventThread-15-localhost:2181] DEBUG o.a.s4.comm.topology.ClustersFromZK - Adding input stream [names] for app [-1] in cluster [cluster1]
  [ZkClient-EventThread-15-localhost:2181] INFO  org.apache.s4.core.App - Init prototype [hello.HelloPE].

Great! The application is now deployed on 2 S4 nodes.

You can check the status of the application, nodes and streams with the “status” command:

./s4 status

Now what we need is some input!

We can get input through an adapter, i.e. an S4 app that converts an external stream into S4 events, and injects the events into S4 clusters. In the sample application, the adapter is a very basic class, that extends App, listens to an input socket on port 15000, and converts each received line of characters into a generic S4 event, in which the line data is kept in a “name” field. We specify :

  • the adapter class
  • the name of the output stream
  • the cluster where to deploy this app

For easy testing, we provide a facility to start a node with an adapter app without having to package the adapter app.

  • First, we need to define a new S4 subcluster for that app:

      S4:myApp$ ./s4 newCluster -c=cluster2 -nbTasks=1 -flp=13000

  • Then we configure the application:

    • we specify the adapter class (app class)

    • we use “names” for identifying the output stream (this is the same name used as input by the myApp app)

    • there is also a -s4r parameter, indicating where to fetch the application package from. We don't need it here, since we skip that step and use a special “adapter” tool

        ./s4 deploy -appClass=hello.HelloInputAdapter -p=s4.adapter.output.stream=names -c=cluster2 -appName=adapter

  • Then we simply start the adapter (there is no packaging and copying of the S4R package)

The adapter command must be run from the root of your S4 project (myApp dir in our case).

	./s4 adapter -c=cluster2

  • Now let's just provide some data to the external stream (our adapter is listening to port 15000):

      S4:~$ echo "Bob" | nc localhost 15000

  • One of the nodes should output in its console:

      Hello Bob!

If you keep sending messages, nodes will alternatively display the “hello” messages because the adapter app sends keyless events on the “names” stream in a round-robin fashion by default.

What happened?

The following figures illustrate the various steps we have taken. The local file system is used as the S4 application repository in our example.

image

What next?

We suggest you take a look at a more comprehensive example application.