At some point, almost every growing app starts having problems. Things that worked fine when you had a few hundred users suddenly get slow, break, or start costing a lot more money. We've seen it happen plenty of times — here's what usually goes wrong and how to get ahead of it before it becomes a real headache.
How You Store Data Matters More Than You Think
One of the first big choices when building a product where lots of different businesses or customers all use the same app is how to keep their data separate. Do you throw everyone into one big pot, give each customer their own section, or build them a completely separate setup?
The "everyone in one place" approach is the cheapest and easiest to start. But if you're not careful, you can end up with a bug where one customer accidentally sees another customer's information — which is obviously a big problem. Completely separate setups per customer are the safest, but they get expensive and complicated fast. The middle ground — giving each customer their own section within a shared setup — is usually what we go with early on. It's a good balance.
The main thing is to make this decision early. It's the kind of thing that's a nightmare to change once the product is live and people are using it.
Payments Are Where Things Get Messy
Billing is genuinely one of the trickiest parts of any subscription product. Payments come through at odd times. Someone cancels mid-month. A card fails but the customer doesn't notice for days. A refund gets processed after the account is already gone.
We've learned to build payment handling so it can survive the weird stuff — duplicate messages arriving, things arriving in the wrong order, delays. The goal is that no matter what happens on the payment provider's side, your records stay accurate and your customers get what they paid for (or don't, if they didn't).
One thing we always say: never just trust what the customer's browser tells you about their subscription. Always check your own records, and make sure those records stay up to date with what your payment provider is telling you.
Don't Make Users Wait for Things That Can Happen Later
Sending confirmation emails, generating PDF reports, resizing uploaded photos — none of this needs to happen while the user is sitting there waiting. If something takes more than a split second, it should happen in the background while the user carries on.
This is one of the most common things we fix when we take over an existing product. Stuff that should be happening quietly in the background is instead making users wait. Once you move it, the app feels noticeably faster even though the total time is the same.
Know When Something Goes Wrong — Before Your Users Tell You
When something breaks at 2am, you want to already know about it — not find out because a customer emails in the morning. Setting up basic alerts so you get a notification when errors spike or things slow down is not complicated, and it saves a lot of pain.
It doesn't matter that much which tools you use. What matters is that you have something in place before you need it. Once something goes wrong is a bad time to start setting up monitoring.
Start Thinking About Growth Before You Need To
The products that handle growth well aren't the ones that were over-engineered from day one. They're the ones where someone, early on, asked "what happens if we get 10 times the users?" and made a few sensible decisions as a result.
You don't need to solve every problem before it exists. But there are a few choices — how you store data, how you handle payments, how you handle slow tasks — where getting it right early makes everything easier later. Get those right and you can build everything else as you go.