Tsung HTTP - User requests out of order / missing / duplicated
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I am currently using the Tsung http feature to try and emulate a large volume of users completing a checkout process. The basic steps are:

Step 1. Land on checkout page

Step 2. Submit checkout form

Step 3. Complete Three D Secure form

Step 4. Take payment

Step 5. Order complete

(tsung.xml: https://gist.github.com/3137802)

We have 3 load balanced web servers that receive these requests. These requests are all logged including the tsung_user_id.

The issue that I am having is that from the web server logs I can see that:

- Some of the user session requests are not hit the web servers in the right order (e.g. request in step 3 is happening before 2)

- Some of the user requests are not hitting a web server at all however proceeding requests for the same user are (step 1 and 4 happen but 2 and 3 are not)

- Some requests are being sent twice (e.g. step 4 happens on webserver1 and webserver2)

If anyone has witnessed anything like this before of has an ideas on what the issue could be it'd be most appreciated.