Why you should never migrate everything at once

You've assessed your environment. You know why you're modernizing. You understand the trade-offs. Now comes the question everyone dreads: How do we actually move this thing? And someone in the room always suggests: "Let's just migrate everything over a weekend." No. Just... no. Why "big bang" migrations fail Big bang means you flip a switch, move everything at once, and hope it works. It's tempting because it sounds simple. It's not simple. It's a disaster waiting to happen. Here's what goes wrong: You can't test everything. You think you can, but you can't. There's always something you missed. You can't roll back easily. Once you've moved 50 services, rolling back means moving 50 services back. Good luck doing that at 2 AM. You can't learn from mistakes. If something breaks, you're fixing it under pressure with everyone watching. You put all your eggs in one basket. One mistake and the entire business is down. The only time big bang works: When you're migrating something so simple it