Lessons from a Failed Migration

Last year, I was part of a team that tried to break a monolith into microservices. We gave ourselves three months. It took nine, and we ended up keeping half the monolith anyway.

Here's what I learned.

The plan looked great on a whiteboard

We drew boxes. We drew arrows. We identified "bounded contexts" and "service boundaries." Everyone nodded. The architecture diagram was beautiful.

The problem is that architecture diagrams don't show you where the pain is. They show you where the boundaries are. Those aren't the same thing.

Mistake #1: We split by nouns, not by change frequency

We created a UserService, an OrderService, a PaymentService. Classic domain decomposition. It felt right.

But the features we shipped most often touched all three. Every sprint, we were coordinating deploys across services that used to be a single database transaction.

# Before: one deploy, one transaction
def create_order(user_id, items):
    user = User.find(user_id)
    order = Order.create(user, items)
    Payment.charge(user, order.total)
    return order

# After: three services, distributed saga, retry logic,
# compensation handlers, eventual consistency...

The "clean" architecture made our most common operation dramatically more complex.

Mistake #2: We underestimated shared data

Services that "own" their data sounds great until you realize that 40% of your queries join across what are now service boundaries. We ended up with:

• Data duplication across services
• Sync jobs to keep duplicates consistent
• Bugs when sync jobs failed silently

We spent more time debugging data consistency than we ever spent dealing with the monolith's "coupling."

Mistake #3: We didn't measure the pain first

The monolith wasn't actually that painful. Deploys took 8 minutes. Tests ran in 4. The codebase was messy but navigable.

We migrated because we thought we should, not because we needed to. The "right" architecture isn't always the one in the blog post. It's the one that fits your team, your scale, and your rate of change.

What I'd do differently

1. Start with the strangler fig pattern — extract one service at a time, not everything at once
2. Split by change frequency, not domain — the thing that deploys 10x a week should be its own service first
3. Measure the pain — if deploys are fast and tests are green, maybe the monolith is fine
4. Keep shared data shared — a read replica is simpler than a sync job

The uncomfortable truth

Sometimes the best architecture decision is to not re-architect. A well-maintained monolith beats a poorly-maintained distributed system every time.

The monolith doesn't care about your architecture diagram. It just works.