A caching strategy: a practical guide

The gap between knowing this and actually doing it is where most teams lose ground. This guide covers what a caching strategy actually involves, where it usually goes wrong, and how to tell whether yours is in reasonable shape.

Real-world numbers from actual visitors matter more than a score produced on a fast laptop. Nothing below assumes a large team or a large budget — most of it is a decision somebody has to make and then write down.

What is actually at stake

The fastest request is the one never made. None of that requires a large budget, only a decision and someone to own it. If it only works because one person remembers to do something, it does not work yet.

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. The cost of getting this wrong is rarely visible on the day it happens.

How to approach it

Cache static assets aggressively with fingerprinted filenames. Where this goes wrong is almost never a lack of knowledge. It is worth deciding this deliberately rather than inheriting whatever the last person set up.

Speed is a feature people notice only in its absence, and then they leave rather than complain. The version that works in practice is usually less elaborate than the version described in the guides.

Decide your invalidation rules before you need them. It is worth being explicit about, because assumptions differ quietly. Budget a little time for it every quarter and it never becomes a project of its own.

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.

• The fastest request is the one never made
• Cache static assets aggressively with fingerprinted filenames
• Decide your invalidation rules before you need them
• 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

Warning signs

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

Performance work is mostly subtraction, which makes it unpopular and effective. That sounds obvious written down. It is still the thing most often skipped.

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?

Making it stick

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. If you are not sure where your systems currently stand on this, it takes us about an hour to find out.