[mod_cluster-dev] Powering down a worker

Bela Ban bban at redhat.com
Wed Jun 9 08:43:06 EDT 2010


I have the scenario where I run httpd/mod-cluster on an EC2 instance and 
a few workers on different EC2 instances.

When I "terminate" a worker instance (using the EC2 GUI), apparently the 
virtual instance is terminated *ungracefully*, ie. similar to just 
pulling the power plug. This means that the shutdown scripts (in 
/etc/rc0.d) are not run, and the open sockets (e.g. to mod-cluster) are 
not closed, so mod-cluster won't remove the worker.

When I look at mod_cluster_manager, it continues listing the killed 
worker in OK state.

My questions:

    * I recall that, unlike mod-jk, mod-cluster doesn't have
      cping/cpong, or any other heartbeating mechanism. Is this correct
      ? So would mod-cluster detect a worker's unreachability, e.g. when
      I pull the plug on the switch connecting the worker to mod-cluster ?
    * I though that the workers detect when a member has crashed and the
      cluster master then notifies the proxy. So when we have workers
      {A,B,C}, and C crashes ungracefully, wouldn't A notify the proxy
      of C's death, so the proxy can remove C ?



-- 
Bela Ban
Lead JGroups / Clustering Team
JBoss



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