We went live with our SAP project approximately 4 weeks ago. We use Apache 2.2 as a reverse proxy with mod_balancer splitting traffic between two SAP portal systems at version 7.0 ehp 1 service pack 7.
In the first 10 days we had two incidents where communication from the Apache reverse proxy to one SAP portal system was consistently failing with a 502 return code, but communication with the other portal system was fine. We do not see anything abnormal in the SAP logs.
The first incident was resolved by restarting just the Apache server while the second required restarting the SAP portal application on the affected system as well.
We are currently examining some leads found on the SAP forum and support site but are looking for input from others to help guide our investigation. The SAP Note 929082 describes a sporadic problem similar to ours except that ours was consistently failing for over 30 minutes.