Be cautious of web.config settings during deployments

A colleague of mine just solved a SharePoint performance issue that pondered our project team for days. The discovery was by accident and the cause is quite classic. I decided to put in as much detail as possible to make this an interesting read. And the story goes... We are building a custom web application that sits on top of SharePoint 2007. Not having enough servers for different phases of the development, a box is allocated for two purpose, training and SIT. Training was installed on the host machine, while SIT is installed as a virtual server on the same box. All went well until suddenly the SIT SharePoint pages were loading at crawling speed. What's funny was that shutting down the SIT would cause the Training instance to slow down as well, but only at MySite. Eventually, the infra team configured their ISA and DNS settings and both servers are working normally again. Weeks gone by until the issue resurfaces when SIT were shutdown again and causes the Training environment to crawling speed. Wouldn't want to bring impact to training, we started back SIT immediately, and decided to look into it later when we have the time (That never happen). By chance, a colleague of mine were setting up a VPC version of the SharePoint application and faces the same performance issue on the VPC. Again, only on happens to MySite. After going through all the web.config settings, making the changes that seems logical, MySite is running at top speed again. What actually causes the problem is due to the Enterprice Library configuration in web.config. One of the parameter of the configuration settings were machineName, which is set to the machine name of the SIT server. This means when the application tries to write logs, it tries to write to the SIT server's Application log. MySite is where enterprise library's logging were used heavily. This explains why:

1. Infra team has to configure ISA and DNS pointing properly so that Training server can write event logs to SIT server. If training server can't find SIT server to write log, it waits until timeout occurs.
2. SIT server shutdown will cause slow down in Training server.
3. VPC version is slow because it was seperated from the LAN and has no access to SIT server.

The moral of the story So why does this happen in the first place? Often we copy web.config for deployment instead of making manual changes to the target environment's web.config files. Copying the settings from SIT server to Training server without making all the necessary changes is the root of this issue.

Therefore, one should go through the whole web.config settings throughly to ensure that the settings are meant for the target deployment environment.