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Zoodiscovery
Contents
What is ZooDiscovery?
ZooDiscovery is a discovery mechanism that runs as an OSGi service. It leverage Apache ZooKeeper robustness and implements Eclipse ECF Discovery API.(Hence the name!). ZooDiscovery is flexible and easy to configure.
This work is funded and made open by Remain Software and Industrial-TSI
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Downland both bundles: org.apache.zookeeper & org.eclipse.ecf.provider.zookeeper
from CVS server at [1]
Anonymous CVS info: :pserver:anonymous@ecf1.osuosl.org:/ecf
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The concept in some words
ZooDiscovery implements both ECF discovery interfaces: IDiscoveryAdvertiser and IDiscoveryLocator. That is, ZooDiscovery can publish our services and gets us noticed about
discovered services. Perfect! But how?
A ZooDiscovery instance running at your machine does its job by exchanging data with other ZooDiscovery instance(s) running elsewhere. So each running ZooDiscovery service must know where that other "elsewhere" exactly is. This is why we should first make our ZooDiscovery happy, giving it an IP address to play with.
To keep it smooth, let's take it step by step following these cases:
Learn by asking
How to tell ZooDiscovery the target I want to connect to?
/*We use the property "discovery.flavor.standalone" to specify we're going to run as standalone(more about this later) and its value is the remote location's IP address we intend to connect to . Please replace with usable IP address(es) when applicable. A comma separated list of one or more IP addresses is valid as well. Something like: "discovery.flavor.standalone=192.1.32.10,192.1.32.11" means our ZooDiscovery instance will connect to both address 192.1.32.10 and 192.1.32.11 where other ZooDiscovery services are running. */ IContainer container = null; try { //"ecf.discovery.zookeeper" is the container name we want to initiate. container = ContainerFactory.getDefault().createContainer("ecf.discovery.zookeeper"); } catch(ContainerCreateException e1){ // TODO } ID target = container.getConnectNamespace().createInstance( new String[] { "discovery.flavor.standalone=192.1.32.10" });
How to get ZooDiscovery service?
IContainer container = null; try { //"ecf.discovery.zookeeper" is the container name we want to initiate. container = ContainerFactory.getDefault().createContainer("ecf.discovery.zookeeper"); } catch(ContainerCreateException e1){ // TODO } ID target = container.getConnectNamespace().createInstance( new String[] { "discovery.flavor.standalone=192.1.32.10" }); try { //we then try and connect. container.connect(target, null); } catch (ContainerConnectException e1) { // TODO } // Connected! Our provider is ready then.
// To advertise services we need adapting our container this way: IDiscoveryAdvertiser discoveryAdvertiser = (IDiscoveryAdvertiser) container.getAdapter(IDiscoveryAdvertiser.class); //then we enjoy calling IDiscoveryAdvertiser contract methods
// To localize/discover services we need adapting it this way: IDiscoveryLocator discoveryLocator = (IDiscoveryLocator) container.getAdapter(IDiscoveryLocator.class); //then we enjoy calling IDiscoveryLocator contract methods
How to build a ServiceInfo object and publish it
//Some service location URI uri = URI uri = URI.create("http://www.example.com/discovery"); //Some service priority int priority = 0; //Some service weight int weight = 3; //Some random service properties ServiceProperties serviceProperties = new ServiceProperties(); serviceProperties.setProperty("foobar", new String("foobar")); serviceProperties.setPropertyBytes("foobar1", new byte[] { 1, 2, 3 }); IServiceTypeID serviceTypeID = null; try { serviceTypeID = ServiceIDFactory.getDefault().createServiceTypeID( DiscoveryContainer.getSingleton().getConnectNamespace(),new String[] {"service1","service2"}, new String[] {"someProtocol"}); } catch (IDCreateException e) {//TODO } //build a service info instance to be published ServiceInfo serviceInfo = new ServiceInfo(uri, "myServiceName", serviceTypeID, priority, weight, serviceProperties); //advertise the service discoveryAdvertiser.registerService(serviceInfo);
I want to get notified about discovered services
You get notified about discovered services by registering yourself as an IServiceListener. Let's take it for a ride and make an inner listener class to see how lightweight its contract is:
IServiceListener sl = new IServiceListener() { public void serviceUndiscovered(IServiceEvent anEvent) { // service lost, do something.. } public void serviceDiscovered(IServiceEvent anEvent) { // new service is in, do something.. } }; //register to get informed discoveryLocator.addServiceListener(sl);
//To register for specific service types discoveries, you might consider registering under IServiceTypeListener
NOTE: ZooDiscovery tracks OSGi services being registered under IServiceListener or IServiceTypeListener, and add them as listeners so that (if you choose to) you don't have to add them explicitly the way we did just above. This is handy when your design is a bit more dynamic/component driven.
Advanced configuration
ZooDiscovery Flavors
Standalone mode: discovery.flavor.standalone
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Centralized mode: discovery.flavor.centralized
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Replicated mode: discovery.flavor.replicated
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Fine tuning the underlying ZooKeeper
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