Plug-in for Singleton Service in Clustered environment and

improving failure detection methodology

Advisor: By:Dr. Chung-E-Wang Srinivasa c Kodali

Department of computer science

California state university, Sacramento

AGENDA

Importance of Singleton service in clustered environment.

Implementation of singleton service.

Need for singleton service as a plug-in

Handling failure detection

Improving failure detection methodologies

Future Developments

Importance of Singleton service in clustered environment

What is singleton service? Service which manages all the singleton objects across the clustered

application.

What are singleton objects? Singleton is a pattern which makes sure that only one instance of that object

is present at any point of time in the application.

Need for singleton services At a time if only one user need to access the JDBC connection. Chat room application in the clustered environment where multiple users

will be sending messages and broadcaster should send the messages to all the clients. Here broadcaster should be only one instance.

Implementation of Singleton Service

Implementation requires all the singleton objects to be accessible only as RMI objects.

Instances of the service code will be present in all the JVM Instances but only one instance of RMI will be started.

If the RMI service is started at one instance then update of JNDI registry should take place which tells where singleton service is running.

JNDI will maintained to know which JVM is running the service and other JVM’s running on the system.

If another server instance need access to singleton object then the instance should make RMI call to the instance where the singleton service is running by looking into the JNDI.

Implementation of Singleton Service cont’d

Service contains a set of API methods which helps to start the RMI service, binding to the JNDI and unbinding the service.

Some of the API methods that plug-in will contain are: start() - will create RMI service on particular server.

Bind() - Bind particular address to the JNDI directory.

unBind() – Un bind the address from the JNDI registry.

getServerInstances() - returns a list of server instances running at that point.

Need for developing a plug-in

Open source servers doesn’t have the singleton service implementation.

Plug-in will reduces the coding time and maintenance capabilities of singleton services in clustered environment.

Plug-in will be compatible with different kind of J2EE application servers like Tomcat, Jetty, glassfish etc.,

Handling failure detection

In clustered environment if the service running the JVM fails, all the singleton objects will not be accessible. It can become single-point failure.

If JVM running the singleton service is down, how would the system know? A monitor in the cluster will be pinging the system which is running

the singleton service at equal interval.

What if the monitor pinging the system is down? A Highly available singleton service need to developed.

How would other system know that the service is down If the monitor can’t ping the system, monitor should be able to start the

another singleton service automatically and update the JNDI directory.

Improving failure detection methodologies

Methodologies to make the singleton service highly available i.e failure detection algorithms: Heart beat method: similar to the Ping system which mentioned above. Async-BFD ( Asynchronous Bi-directional forwarding detection method) : In

this method any two nodes( can be random node, neighbor node) should be able to establish a communicate channel for a period of time. In the channel the nodes should send messages (ping) each other. If the ping node

gets the reply back then other node alive. This method can eradicate any single point failure.

Future Developments

This methodology can be extended to cluster the instances like JMS etc.,

Electing server to start the singleton service (failover detection) can be challenging task. Can use using complex distributed algorithms like leader- election algorithm.

Questions

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