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Web server SSL Overhead

Hello All,

I'm building a very high volume web site which needs to be as lean and mean as possible.  The site will be sustained by advertising so it needs to be very efficient.  What kind of performance overhead is accepted by using SSL protection?  How much more server memory, CPU, and bandwidth will be consumed if I use SSL for each user's session?

(I'm using IIS7 configured as a web farm; via SQL Server state management)
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Phil5780
Asked:
Phil5780
2 Solutions
 
RouchieCommented:
This question gets asked quite frequently, but unfortunately the figures vary depending on the nature of the site.  Some people estimate that HTTPS is approximately 10 times slower than HTTP, however, this delay is caused by the initial handshake process (when the client and server exchange encryption data) rather than the transfer of files.

This site http://stackoverflow.com/questions/149274/http-vs-https-performance recommends that you create the site then use a profiler tool to check the resource usage (first with HTTP, then HTTPS).

I run a very large web application that is entirely delivered using HTTPS.  I can't say I've really noticed any difference is resource usage, or speed, although I am sure there is some to a degree.

Does your entire app need to use HTTPS, or can you switch to HTTPS for particular elements such as login, account admin, payment?
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giltjrCommented:
Bandwidth, I am assuming you are talking network, is not really effected by SSL.  

CPU, the big hit in CPU is (as Rouchie stated) the initial handshake.  The overhead of doing the actual encryption/decryption is not that much and depends on the same of the pages. So it depends on how many SSL connections you are going to be doing.  When you read about SSL transactions per second this is typically referring to SSL handshakes per second,  not the number of "https" hits.

Memory usage will vary.  It depends on the size of the pages (actually the individual files that make up the pages) you are serving.  Since you need to hold the page in memory twice for a small time period memory utilization will increase.  However, since most files are small it should not matter that much.


Going down the path Rouchie started, only encrypt what you must.  In fact since the site will be sustained by advertisements, I would suggest that if possible the adds are served up by a server other than the app server and none of the ads should be encrypted.  Now if the page is encrypted this will cause the dreaded "mixed" content messages.
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Phil5780Author Commented:
SSL is unnecessary then for my site.  It just add unnecessary security for data that's just not that important.
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