Skip to main content

Implementing a Simple Http server within Java client

I have to implement BDB replication for backup purpose. We cant afford to miss any commits. we do checkpoint every 2 mins but loosing even 2 mins of data can be catastrophic, therefore we are going to use a simple Java client that will open BDB as a replica and Master will sync every change to this guy and only then it will commit.

Now the challenge was to verify the replication I wanted to print something from this replica or I wanted to stop this replica gracefully. Implementing a shutdown hook wasn't working because kill -9 wasn't calling it and I have to implement some other operations on this Java client. Instead of juggling around with commandline or some RPC I used a simple Http server from Java.
private void init() {
        InetSocketAddress addr = new InetSocketAddress(httpServerPort);
        httpServer = HttpServer.create(addr, 0);
        HttpContext context = httpServer.createContext("/", new AdminOpsHandler());
        httpServer.setExecutor(Executors.newCachedThreadPool());
        context.getFilters().add(new HttpParameterFilter());
        httpServer.start();
        logger.info("Server is listening on http port " + httpServerPort);
}

    class AdminOpsHandler implements HttpHandler {
        @SuppressWarnings("unchecked")
        public void handle(HttpExchange exchange) throws IOException {
            String requestMethod = exchange.getRequestMethod();
            logger.info("Processing http request");
            if (requestMethod.equalsIgnoreCase("GET")) {
                Map params = (Map) exchange.getAttribute("parameters");
                String command = (String) params.get("cmd");
                Headers responseHeaders = exchange.getResponseHeaders();
                exchange.sendResponseHeaders(200, 0);
                PrintWriter responseBody = new PrintWriter(exchange.getResponseBody());
                responseHeaders.set("Content-Type", "text/plain");
                if ("stop".equals(command)) {
                    responseBody.write("Triggering stop of client");
                    logger.info("Triggering stop of client");
                    try {
                        cleanup();
                    } catch (ApplicationException e) {
                        throw new IOException(e);
                    }

                } else if ("print".equals(command)) {
                    String workgroupId = (String) params.get("wgid");
                    responseBody.write("Printing workgroupId" + workgroupId);
                }
                responseBody.close();
            }
        }
    }


The challenge was to fetch request parameters from the HttpExchange and then this post from a fellow programmer came handy. Looks like I am becoming Google programmer ;).

http://leonardom.wordpress.com/2009/08/06/getting-parameters-from-httpexchange/

Comments

  1. The main thread initializes the server and starts a number of worker threads that will handle client connections. The worker threads simply wait around idle until there's a client to service. The main thread then accepts connections from clients, passes off the connection for a worker thread to handle, and continues accepting new connections.

    ReplyDelete

Post a Comment

Popular posts from this blog

RabbitMQ java clients for beginners

Here is a sample of a consumer and producer example for RabbitMQ. The steps are
Download ErlangDownload Rabbit MQ ServerDownload Rabbit MQ Java client jarsCompile and run the below two class and you are done.
This sample create a Durable Exchange, Queue and a Message. You will have to start the consumer first before you start the for the first time.

For more information on AMQP, Exchanges, Queues, read this excellent tutorial
http://blogs.digitar.com/jjww/2009/01/rabbits-and-warrens/

+++++++++++++++++RabbitMQProducer.java+++++++++++++++++++++++++++
import com.rabbitmq.client.Connection; import com.rabbitmq.client.Channel; import com.rabbitmq.client.*; public class RabbitMQProducer { public static void main(String []args) throws Exception { ConnectionFactory factory = new ConnectionFactory(); factory.setUsername("guest"); factory.setPassword("guest"); factory.setVirtualHost("/"); factory.setHost("127.0.0.1"); factory.setPort(5672); Conne…

Logging to Graphite monitoring tool from java

We use Graphite as a tool for monitoring some stats and watch trends. A requirement is to monitor impact of new releases as build is deployed to app nodes to see if things like
1) Has the memcache usage increased.
2) Has the no of Java exceptions went up.
3) Is the app using more tomcat threads.
Here is a screenshot

We changed the installer to log a deploy event when a new build is deployed. I wrote a simple spring bean to log graphite events using java. Logging to graphite is easy, all you need to do is open a socket and send lines of events.
import org.slf4j.Logger;import org.slf4j.LoggerFactory; import java.io.OutputStreamWriter; import java.io.Writer; import java.net.Socket; import java.util.HashMap; import java.util.Map; public class GraphiteLogger { private static final Logger logger = LoggerFactory.getLogger(GraphiteLogger.class); private String graphiteHost; private int graphitePort; public String getGraphiteHost() { return graphiteHost; } public void setGraphite…

What a rocky start to labor day weekend

Woke up by earthquake at 7:00 AM in morning and then couldn't get to sleep. I took a bath, made my tea and started checking emails and saw that after last night deployment three storage node out of 100s of nodes were running into Full GC. What was special about the 3 nodes was that each one was in a different Data centre but it was named same app02.  This got me curious I asked the node to be taken out of rotation and take a heap dump.  Yesterday night a new release has happened and I had upgraded spymemcached library version as new relic now natively supports instrumentation on it so it was a suspect. And the hunch was a bullseye, the heap dump clearly showed it taking 1.3G and full GCs were taking 6 sec but not claiming anything.



I have a quartz job in each jvm that takes a thread dump every 5 minutes and saves last 300 of them, checking few of them quickly showed a common thread among all 3 data centres. It seems there was a long running job that was trying to replicate pending…