Migrate License Keys Without Breaking Existing Customers

Originally published on the Keylight blog . The thing that stops developers from moving their licensing isn't the work. It's the fear of one specific moment: a paying customer opens the app after you've switched, and it tells them they're unlicensed. That's the nightmare — you reach for lower fees and customer ownership, and the bill comes due as a wave of "I already paid for this" support tickets. It's a reasonable fear, and it's also avoidable. Migrating onto Keylight doesn't require invalidating anything, re-issuing anything, or asking customers to do anything. This post is about the one rule that keeps everyone working, the two situations you might be in, and why a scary-sounding "major version" jump changes none of it. When you're ready for the click-by-click mechanics, the companion piece covers them: How to Import an Existing Customer Base into Keylight . Why migrating licensing feels risky A license check is binary in the moment a customer experiences it: the app either lets them in or it doesn't. So any change to the system behind that check feels like it's playing with a live wire. Switch the layer that answers "is this person allowed in," the thinking goes, and you risk every existing customer getting the wrong answer at once. That instinct is right about the stakes and wrong about the mechanism. The wave of lockouts people picture comes from one specific mistake: treating migration as a cutover , where the old keys stop being recognized the instant the new system goes live. If your migration invalidates the old keys, yes — everyone breaks. The entire trick is to not do that. The one rule: old keys stay valid Here's the rule the whole migration hangs on: you bring your customers' keys in as they are, and nothing gets invalidated. When you import an existing customer, their license is a live, active record from the first second. If you include the key string they already have, that key is what Keylight stores — not a replacement. So when your new build ask