Maximum concurrent connections with CSG 3.0

[Nathan Anthony]

This question has been confusing me for quite a few weeks and there is no information on the subject out there on the internet at present. I am currently involved in a 20,000 concurrent users PS4 implementation where we are using CSG. the big question was why is there a hard coded limit in CSG 3 of 1670 concurrent users. There is information that this can be increased to 1920 users by removing the 250 for httboost in the conf file. Question i had was why is this limit hard coded as it wasnt with CSG 2.

OK CSG 3 is based on Apache and CSG2 wasnt so i figure it must be something to do with that. After much chasing of Citrix resources around the world I have an answer.

The limit of 1670 is based on the fact that CSG3 runs as one process. A process in 32bit windows can only use 2048 MB of RAM. Unless the PAE /3gb swicth is used but this is not recommended. Each thread (one concurrent connection creates a thread) uses 1mb of memory. So with a process being able to cope with 2000 connections then this would be the maximum number of connections you can support. Its pretty much that simple except for the fact that you still have the httpboost setting, this is used for the consideration that maybe more than one connection will be requested at any one time. You need some resource to deal with those connections which is why Citrix have decreased the max connections by 250. OK you say this leaves us 1750 not 1670 so why do they limit it to 1670. This is due to other processes and events that may have not been predetermined, its considered a buffer so not to max out the server completely.

Therefore in summary no matter how fast your harwdare is you will not be able to get more than between 1670 and 1750 concurrent connections to a single CSG 3 server. 2000 at the most but this does depend on many factors specific to each environment.

I'm therefore going to use 14 CSG servers behind two hardware load balancers (F5) to cope with the 20,000 user concurrency.

I also considered the Citrix Access Gateway but this wouldnt have really helped. The CAG also has a limit of 2000 concurrent users and a cost associated of approx. $90 USD per concurrent user.

I hope that answers the questions on loading of CSG and CAG. If you have any more questions or concerns feel free to post them on the forum.

[Nathan Anthony]

Since writing this 4 years ago there are new options available. Check out the entry level Netscalers available as these would have been included in the design if there were available then.