Manage Tomcat queued connections

[herau]

Adding two tomcat server properties:

• server.tomcat.accept-count
• server.tomcat.max-connections

Fixes #6433

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[philwebb]

Thanks. I'll target this to 1.5. We should also look to see if Jetty/Undertow have similar options that mean this could be a top level property.

[herau]

Ok i will check it.

[herau]

@philwebb
Tomcat has an acceptCountoption

The maximum queue length for incoming connection requests when all possible request processing threads are in use. Any requests received when the queue is full will be refused. The default value is 100.

and a maxConnections option

The maximum number of connections that the server will accept and process at any given time. When this number has been reached, the server will accept, but not process, one further connection. This additional connection be blocked until the number of connections being processed falls below maxConnections at which point the server will start accepting and processing new connections again. Note that once the limit has been reached, the operating system may still accept connections based on the acceptCount setting.

Jetty has an acceptQueueSizeoption:

The size of the pending connection backlog. The exact interpretation is JVM and operating system specific and you can ignore it. Higher values allow more connections to wait pending an acceptor thread. Because the exact interpretation is deployment dependent, it is best to keep this value as the default unless there is a specific connection issue for a specific OS that you need to address.

But i don't find any option for the limitation of connections number :-( maybe it's already available with server.jetty.acceptors?

Undertow provide a RequestLimitingHandler which allow to define the maximum concurrent requests and the the maximum number of requests to queue

So you could use a generic option to set the max number of requests to queue with a key like server.max-requests-queue-size; are you ok with that ?

[philwebb]

@herau Thanks for the detailed analysis. It looks like the different implementations are probably different enough that a uniform property isn't the best approach after all. We're just merge your PR as it is and keep it Tomcat specific.

Thanks!