Rate limiting: a practical guide

Every audit we run turns up some version of this. This guide covers what rate limiting actually involves, where it usually goes wrong, and how to tell whether yours is in reasonable shape.

The cheapest security work is the boring kind done on a schedule. Nothing below assumes a large team or a large budget — most of it is a decision somebody has to make and then write down.

Why it matters

Unlimited endpoints get abused eventually. In practice this is a scheduling problem more than a technical one. It is the sort of thing that looks like polish right up until it costs you an enquiry.

For most businesses the question is not whether this matters but how much of it is worth doing right now. That depends on what you are trying to achieve in the next few months, not on best practice in the abstract. Where this goes wrong is almost never a lack of knowledge.

Where to start

Limit by account and by address. The teams that handle this well are rarely the ones with the biggest budgets. It is the sort of thing that looks like polish right up until it costs you an enquiry.

Security is a maintenance habit rather than a purchase, which is why it drifts. The version that works in practice is usually less elaborate than the version described in the guides.

Return a clear response instead of failing silently. In practice this is a scheduling problem more than a technical one. The version that survives contact with a real deadline is the simple one.

A working checklist

If you want a quick read on where you stand, work through this. Anything you cannot answer confidently is where to start.

• Unlimited endpoints get abused eventually
• Limit by account and by address
• Return a clear response instead of failing silently
• Someone is named as the owner, not just assumed to be
• There is a date in the calendar to review it again
• The decision and the reasoning behind it are written down somewhere findable
• You could explain the current setup to a new hire in five minutes

What to watch for

The most common failure is not doing this badly. It is doing it once, during a launch, and never revisiting it. Circumstances move, the setup does not, and the gap widens quietly until something breaks or somebody notices the numbers.

• It was configured during a launch and has not been touched since
• Different people in the business believe different things are true about it
• There is no way to tell whether the last change helped or hurt
• The only person who understands it has left, or is about to

The realistic threat for most small businesses is automated and opportunistic, not targeted. None of that requires a large budget, only a decision and someone to own it.

How we approach it

On our projects this gets handled during the build rather than added afterwards, because retrofitting it costs several times more than including it. We write down what was decided and why, so the next person to touch it is not guessing.

If you are working with someone else, the questions worth asking are simple: who owns this, how will we know it is working, and what happens when it needs to change?

What to do next

Pick the single item from the checklist above that would cause the most trouble if it turned out to be wrong. Fix that one, confirm it worked, then move on. The point is not perfection, it is knowing which of these you have consciously chosen to skip.