[stunnel-users] Stunnel Scalability Question

Michal Trojnara Michal.Trojnara at mobi-com.net
Sun Jul 29 09:40:24 CEST 2007

On Wednesday 18 July 2007 19:14, Ankur Upadhyaya wrote:
> 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):

You can study some useful benchmarks available here:

> - 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)
> disconnecting.

To estimate CPU requirements you first need to estimate maximum traffic (it is 
likely much lower than the number of concurrent connections multiplied by 
their throughput) and the maximum number expected new connections per second.  
Both depend on your application.

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

For 2000 concurrent clients you need about 300MB of memory for stunnel 
process.  Depending on your platform you may need some additional settings.
Send us the output of "stunnel -version".

> (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
> disconnecting)?

You don't have any reason to believe that.

> (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.

CPU usage is probably not an issue.  There are many even more loaded stunnel 
installations worldwide.

Best regards,
	MichaƂ Trojnara
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