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We are running into issues with BizTalk host instance intermittently going down. One of the things that we are worried about is the number of FTP connections a single host instance is making which could easily reach into the hundreds perhaps sometimes thousands, depending on traffic.

My question is Windows Server 2003 Is there a limit on number of TCP connections per process? If so would putting each application in it's own host instance potentially solve the problem.

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You know, this is something that isn't addressed in Mark R's "pushing the limits" series. blogs.technet.com/b/markrussinovich/archive/2009/09/29/… –  mfinni Feb 10 '11 at 14:43
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There's a lot of other things that are likely to be exhausted before you run out of TCP connections. An FTP server should not crap out for a few thousand connections.

Read this article and the rest of the series. Plus, just do your normal troubleshooting. Anything in the windows System or Application event logs? Is there an application log that you could review? Do the IIS logs tell you anything (assuming IIS is your FTP server)?

There's a lot of things you need to check on before you start guessing that you've run out of TCP connections.

OK - here's a pretty good link for you to start looking into then. That's a lot of new info for me, and I'm still a little surprised that Mark R hasn't delved into it. Of course, it has little to do with kernal data structures except for the TCB, so maybe he doesn't much care :-)

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The FTP server BizTalk is connecting to is a iSeries Mainframe Unix box that our group has no control over. Also the weird thing is that there is absolutely no errors or warning in the system or application event log, which is what has us scratching our heads. We have also run biztalk health check which has yielded no red flags, though we have not run it long enough for the instance to shut down. –  aceinthehole Feb 10 '11 at 14:55
Stupid question, but do THEY have a connection limit in place? ;) –  TomTom Feb 10 '11 at 14:57
I'm not sure I'm understanding you. The BizTalk instance is running on your Windows server, and the mainframe is making FTP connections to your Windows machine? That means that your windows machine is running an FTP server. Unless I've misunderstood you - if the Windows machine is making FTP connections to the mainframe? –  mfinni Feb 10 '11 at 15:02
The windows server is making connections to (outbound) the mainframe, it is polling directories hosted on the mainframe. Also we have confirmed that they have configured their FTP server for an very large number of concurrent ftp connections, though I am unsure if the max number of TCP connections on that box is an issue. I assume that a windows box would run into problems with an issue like that before a mainframe would. –  aceinthehole Feb 10 '11 at 15:20
If the FTP server (mainframe) set a limit, then you would simply get failures from your FTP client, I very much doubt that it would make your biztalk process fall down. I don't know a ton about biztalk first-hand, so you're going to have to troubleshoot from there. I think that you're barking up the wrong tree by spending too much time thinking that you're running out of TCP connections on your windows machine. –  mfinni Feb 10 '11 at 15:48
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