Blue/Green Deployments: Deploy changes in parallel and switch traffic to the new?

Short answer: schema only after all microservices have been updated to handle the new schema.

Example code

If the Order Service needs to add a new field (e.g., discount_code), you might first add it as nullable, update the services to start using it, and then later remove old fields.

Real-world example (ShopNest)

ShopNest splits Catalog, Cart, Order, and Payment into services so teams can deploy catalog changes without redeploying payments.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.