Skip to main content

RateLimiting based on load on nodes

We are a cloud based file storage company and we allow many access point to the cloud. One of the access point is Webdav api and people can use any webdav client to access the cloud. But some of the webdav client especially on mac OS are really abusive. Though the user is not doing any abusive action, the webdav client does aggressive caching so even when you are navigating at a top directory it does PROPFINDs for depth at 5 or 6 level to make the user experience seamless as if he is navigating local drive. This makes life miserable on the server because from some clients we get more than 1000 requests in a minute. If there are 5-10 clients do the webdav activity then it causes 100 or more propfinds per sec. Luckily the server is able to process these but it hurts other activities. So we needed to rate limit this. Now as the user is really not doing any abusive action it would be bad to slow down on penalize the user in normal circumstance, however if the server is under load then it would be worth while to throttle the user for some time.

Luckily Jdk1.6 has a light weight api to get system load average.

 public double getSystemLoadAverage() {
  OperatingSystemMXBean osStats = ManagementFactory.getOperatingSystemMXBean();
  double loadAverage = osStats.getSystemLoadAverage();
  return loadAverage;
 }

And now I can write code like

  if(throttlePropFinds(req, user)) {
   logger.info("Throttling due to excessive webdav requests from user {}", user.getId());
   if(throttlingHelper.isBlockUsers()) {
    double loadAverage = SpringBeanLocator.getJvmStatsLogger().getSystemLoadAverage();
    if (loadAverage > 4) {
     logger.info("Sending 503 as loadAverage>4 and excessive webdav requests from user {}", user.getId());
           resp.sendError(WebdavStatus.SC_SERVICE_UNAVAILABLE);
           return;
    }
   }
  }

The logic I used for propfind rate limiting is simple where I keep track of all users who made>1000 requests in last 5 min and only if loadAvg is >4, I send 503. For brevity I am not putting the code to count no of request made by users in last 5 min but I am using memcache to maintain the counters in one minute buckets.

Comments

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 Erlang Download Rabbit MQ Server Download Rabbit MQ Java client jars Compile 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.se...
23 comments
Read more

Spring 3.2 quartz 2.1 Jobs added with no trigger must be durable.

I am trying to enable HA on nodes and in that process I found that in a two test node setup a job that has a frequency of 10 sec was running into deadlock. So I tried upgrading from Quartz 1.8 to 2.1 by following the migration guide but I ran into an exception that says "Jobs added with no trigger must be durable.". After looking into spring and Quartz code I figured out that now Quartz is more strict and earlier the scheduler.addJob had a replace parameter which if passed to true would skip the durable check, in latest quartz this is fixed but spring hasnt caught up to this. So what do you do, well I jsut inherited the factory and set durability to true and use that public class DurableJobDetailFactoryBean extends JobDetailFactoryBean {     public DurableJobDetailFactoryBean() {         setDurability(true);     } } and used this instead of JobDetailFactoryBean in the spring bean definition     <bean i...
7 comments
Read more

Killing a particular Tomcat thread

Update: This JSP does not work on a thread that is inside some native code.  On many occasions I had a thread stuck in JNI code and it wont work. Also in some cases thread.stop can cause jvm to hang. According to javadocs " This method is inherently unsafe. Stopping a thread with Thread.stop causes it to unlock all of the monitors that it has locked". I have used it only in some rare occasions where I wanted to avoid a system shutdown and in some cases we ended up doing system shutdown as jvm was hung so I had a 70-80% success with it.   -------------------------------------------------------------------------------------------------------------------------- We had an interesting requirement. A tomcat thread that was spawned from an ExecutorService ThreadPool had gone Rogue and was causing lots of disk churning issues. We cant bring down the production server as that would involve downtime. Killing this thread was harmless but how to kill i...
6 comments
Read more