Hi Lei, that's a good question -- DOS attack. We had a few cases where clients were creating infinite numbers of sessions and never closing them due to programming bugs. This results in the ZK service maxing out resources (typically file descriptors) and failing. This is very bad from an availability perspective so to protect against this we added a limit. The good thing is that this limit was made configurable, so you can set it however you like:

See "maxClientCnxns" here: http://bit.ly/9nAowJ


On 04/27/2010 05:17 PM, Lei Zhang wrote:
Sorry for hijacking this thread.

By default the server will only allow 10 sessions to be active from a
particular client (ip), perhaps you hit this and it triggered the storm?

I am very surprise to hear about this limit. Our system has a number of
daemons using zookeeper service, each daemon maintaining a zk session. I am
in the process of changing to each thread of each daemon maintaining a zk
session. That means we will hit this 10 session limit very easily.

Patrick - what is the rationale for this 10 session limit?


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