[stunnel-users] Stunnel Scalability Question

Ankur Upadhyaya ankur at ca.ibm.com
Wed Jul 18 19:14:20 CEST 2007


I have an application with the following characteristics and am trying to 
determine if Stunnel would be a suitable option for securing my 
transmissions (in particular, will it scale):

- Each of my clients is connected to the Internet via a 56Kbps modem.  My 
server has whatever bandwidth it needs.

- Each client "transaction" consists of (a) connecting to a central server 
using a TCP/IP-based protocol, (b) uploading a 512KB block of data and (c) 

- Our server needs to be able to handle 2000 concurrent clients under peak 

- Under the peak load above, I would like to limit the time a client takes 
to perform a "transaction" to around five minutes or so (uploading 512KB 
at (56Kbps / 2) = 28Kbps should take ~2.5 minutes). 

My questions are:

(1) Do I have any reason to believe that Stunnel will simply not be able 
to scale to handle the load described above (i.e. a steady load of 2000 
concurrent clients connecting, uploading half a megabyte of data and 

(2) If Stunnel can handle this - do you have any thoughts on what sort of 
machine (or machines) I should be running my server-side Stunnel daemon(s) 
on?  I am particularly concerned about CPU usage.

I apologize in advance for any overlap between this query and past threads 
in the archive/information on the website - I wanted to make sure that I 
ran the specific requirements above past somebody with experience using 


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