Caveat: These are recommendations only and it is recommended that customers refer to Tomcat documentation, for the version you're using, and use a performance testing optimisation strategy to optimally configure IG according to their deployment. Only an incremental optimisation strategy will determine the optimal configuration for a given deployment and user load.

See Tomcat documentation:

See IG documentation and blogs:

Tuning the Tomcat Container JVM

See Tuning the JVM.

Tomcat Connectors

In order to configure IG on Tomcat, it is important to note Tomcat version and configured connector type. Below is a list of the Tomcat 8.x and 9.x Connector types, with some pertinent qualities of each:

Java Blocking Connector BIO (Tomcat 3.x - 8.x)

Java Nio Connector NIO (Tomcat 6.x+)

Java Nio2 Connector NIO2 (Tomcat 8.x+)

BIO versus NIO

While there are potential performance gains to be had in selecting the NIO Connector over the BIO Connector, it is not certain. It is largely determined by the server usage. The main advantages to be gained are:

GSA: I think we should just describe NIO stuff: IG is built for async processing, that would be a non-sense to advertise blocking behaviours! So, I would move your writing on NIO/NIO2 diff here

WM: Same point really, it's useful to know for us and the field. If they encounter BIO, what does it mean? Not intended for our docs though...

(Will remove Tuesday 30/6/2020 if no further comment)

To take advantage of IG's asynchronous thread model, it is recommended that the Tomcat container is configured to use an NIO or NIO2 Connector. Please refer to Tomcat 8.x or Tomcat 9.x documentation for a comparison. 

Connector Configuration

In order to configure IG on Tomcat, the following Tomcat connector configuration options are worthy of consideration:


The maximum number of connections that the server will accept and process at any given time:

  • default is 10,000 for BIO or 8192 for NIO/ NIO2
  • For NIO/ NIO2, this value can be set to -1 and connections will not be counted.

The available time for connecting to a server-side socket, before timing out and abandoning the connection attempt.


The socket timeout, after which the request is deemed to have failed.

acceptCountThe maximum queue length to queue incoming requests when all threads are busy - default is 100.

An Executor can be configured to manage the Connector  thread-pool - rather than configuring thread-based options directly on the Connector . This supports the sharing of an Executor  between Connector s. Note that this is specially recommended to provide finer control over server resources, notably threads.

Refer to Executor config.


The maximum number of request processing threads to be created by this Connector, which therefore determines the maximum number of simultaneous requests that can be handled - default is 200. This can also be configured via the executor.

GSA: I would just focus on executor options (there is a maxThreads here as well)

WM: There is... The thing is, the executor  is actually intended to allow multiple Connector s to use a single Executor  (with common config). If a Connector  does not have this configured then it uses its own config, which in turn actually creates :drumroll: an Executor for it to use (privately).

Maybe I should make a note of this?

GSA: that looks like to me that executor is the Tomcat "supported" way, while maxThreads are still here for backward compatibility

(Will remove Tuesday 30/6/2020 if no further comment)


The minimum number of threads that should be available, idle or active, at any given time - default 10. This can also be configured via the executor.

GSA: probably part of the executor config right ?

WM: It's part of both - plain `Connector` and a `Connector#executor` config.

(Will remove Tuesday 30/6/2020 if no further comment)

See Tomcat docs for 8.x and 9.x for more information.

The following Tomcat Connector configuration options should be considered:

  • maxConnections
  • connectionTimeout
  • soTimeout
  • acceptCount
  • executor
  • maxThreads
  • minSpareThreads

Please refer to Tomcat 8.x or Tomcat 9.x documentation for a comparison. 

Configuring IG on Tomcat

See Tuning IG and the ClientHandler/ ReverseProxyHandler


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