When Reverse Proxies Surprise You: Hard Lessons From Operating at Scale

It's nice to see someone else preaching this:

> Production Lesson: Never let exceptions dictate the norm. Handle them explicitly, in isolated paths or tiers, instead of polluting the mainline logic. What looks like "flexibility" is often just deferred fragility waiting to surface at scale.

I've seen this pattern far too often in production systems. In the name of "covering edge cases", a huge amount of complexity is moved over to configuration languages, interfaces, APIs, etc, to be more flexible. Not only this doesn't free up the developers time (because it overcomplicates it all), it also makes things worse on the other side for the users of such structures. We already have something "flexible": source code itself, no need to reinvent the wheel.

Very interesting read! But I want to point out a small correction - the DNS collapse issue at HAProxy, along with O(N^2), also had some O(N^3) code paths, which is just mind-blowing.

Also, I believe this should be the correct GitHub issue link - https://github.com/haproxy/haproxy/issues/1404

> Production Lesson: Code that "works fine" at small scale may still hide O(N²) or worse behavior. At hundreds or thousands of nodes, those costs stop being theoretical and start breaking production.

Re-sort the takeaway points, to put this one first:

> Prioritize human factors. Outage recovery depends on what operators can see and do under stress. When dashboards fail, clear logs, simple commands, and predictable behavior matter more than complex mechanisms.

Why - to make it really, really clear to bullet-skimming managers and complexity-loving engineers that too-clever "solutions", and just-an-afterthought "testing & training", and poorly documented configurations will turn into worlds of pain when things really go wrong. The "smart people" won't be in the Operations Center then. Let alone with all the details fresh in their minds. And several of them may have taken jobs elsewhere, to not much care if the org is desperate for their help right now.

The engineer killing the proxy because they assumed processes running as "nobody" were stray (whatever that means - processes without a parent don't change username, and nobody doesn't mean no username) doesn't belong in that list. That was just an engineer out of their depth (I assume one used to dealing with other systems)