In my last post, I talked about the venerable tcpdump tool. For load balancing, it’s a critical tool for diagnosing issues.
Another tool, equally as critical, is an HTTP header-sniffer. For Firefox, one such tool is Live HTTP Headers. For Internet Explorer, there’s ieHTTPHeaders.
Both of these tools do essentially the same thing, which is to allow you to see the HTTP header communications between your browser and the server that it’s communicating with. With the advent of Layer 7 load balancers, it’s helpful to see what the load balancer is injecting (typically cookies) and to verify that everything is working correctly. It’s also helpful to resolve 304 redirect issues, which are problems that typically the result of a server configuration issue, but end up being blamed on the load balancer (blaming the load balancer? That never happens!).
Above is a screenshot of Live HTTP Headers in action. It shows the URL, the request that my browser formed (including any existing cookies, such as “rememberme”, and the response from the server (HTTP/1.x 200 OK).
These are great tools for figuring out where an odd redirect might be coming from, or why an image doesn’t show up. I never leave home without them.
