A great deal of effort has been put into the Kemp LoadMaster load balancing products to eliminate the complexity of application deployment. However when issues do occur, it’s essential to be able to identify and drill down to the root of the problem. Troubleshooting is not about knowing everything about a device or product that is having an issue, It is really about eliminating possibilities until you come to a logical conclusion that this must be the issue at hand.
When I troubleshoot on the LoadMaster, I like to take the bottom to top approach by beginning at the specific and moving to the general. With one exception which is the OSI model, which in all honesty I cheat and skip a few layers by usually starting at layer 3 which I will explain below. This post is designed to walk you through the 5 steps I take when I help a Kemp customer troubleshoot the LoadMaster.
Physical
Without getting too technical, this is the actual physical connection. The age-old troubleshooting technique, “is it plugged in?”
Logical
This is the layer where switches operate. Think ARP. Where are you LoadMaster?
Network
I typically start with routing, I start here because most LoadMaster issues are quickly resolved by correcting routing issues. A lot of issues customers face are due to network/routing issues on or around the LoadMaster. So, no matter the issue I double check a few things before even looking at the VIP configurations.
- Look at interface settings
- What is the default gateway? Does it differ from the VIPs default gateway?
- Any additional routes?
- What are we connecting from/client IPs?
- Where is traffic flowing from and going to?
Transport
Next up is the transport layer, this one is simple as it’s all about ports. Here we have TCP/UDP. Mainly TCP since HTTP/S uses this. Everyone has their favorite.
- Can I connect the desired port directly to the server?
- Is a firewall or something else blocking port access to the VIP?
Application
Last, but not least we have HTTP/S. This is arguably the biggest and most used protocol for the application layer on the LoadMaster. There are others such as SMTP. Here we can check the application layer. Beyond that though we can go ahead and bundle up configuration settings on the VIP itself.
- Does connection work going directly to the server?
- Is the request formatted incorrectly (bad URL, invalid mailbox, etc.)?
- Are there any configurations on the VIP we can eliminate to make things simpler?
- Does it work once we eliminate some settings?
If for instance you turn off ESP and the connection works, you can safely assume something in the ESP setting is misconfigured and you know where to begin.
Conclusion
It is all about getting a baseline, once we have this we have narrowed down our search significantly. Using the OSI model to structure your troubleshooting provides a good framework for managing the process. I hope this helps you in troubleshooting your Kemp LoadMaster.
