Data contracts without the ceremony

The phrase “data contract” makes people think of meetings and sign-off documents. A contract can be much smaller.

The smallest useful contract

A contract has three parts:

1. A schema that the producer agrees to keep.
2. A test that runs when the schema changes.
3. A person who gets the alert.

In dbt, the first two parts fit in one YAML file:

models:
  - name: orders
    config:
      contract:
        enforced: true
    columns:
      - name: order_id
        data_type: string
        constraints:
          - type: not_null

Who gets the alert

Send the alert to the producer, not the consumer. The producer can fix the problem. The consumer can only complain about it.

When to add ceremony

Add a review step when a contract change breaks a paying customer. Until then, keep the contract in code and let the tests do the talking.