if the semantics of your problem change

then everything else needs to change

prevent implementation coupling, that makes your architecture brittle

contracts: strict vs loose

method calls

"schema"

serialized objects

RPC remote procedure call

graphql (aggregation framework, not a invocation framework)

value-driven contracts

json

KVP key value pairs

example: brittleness

not brittle: changing the type of country, does not break the contract for wishlist

support all versions forever? => deprecation strategy

https://martinfowler.com/articles/consumerDrivenContracts.html

pact

• sync: rest

• async: events (kafka / rabbitmq)

looser?

• deployability (delay in updating versions in app store, old versions on customer phones)

• integration points (app stores)