The correct answer is Rely on direct synchronous coupling between services. Engineers should avoid designing microservices that depend on tight synchronous calls because that pattern creates brittle, hard to scale systems.

Rely on direct synchronous coupling between services leads to cascading failures and latency propagation when one service slows or fails. It also prevents teams from deploying and scaling services independently and makes fault isolation and testing much harder.

Prefer decoupling patterns such as asynchronous messaging, event driven flows, retries with backoff, and resilience patterns like circuit breakers and bulkheads. These approaches reduce the blast radius of failures and improve scalability without requiring tight coordination between services.

Use Cloud Pub/Sub for decoupled asynchronous messaging is not the correct choice to avoid because it represents a recommended way to decouple services rather than a harmful practice. Messaging systems are an example of how to avoid synchronous coupling.

Use an API gateway for centralized ingress and routing is useful for managing external traffic and enforcing cross cutting concerns, but it does not answer the question about which practice to avoid. An API gateway helps with routing and security but it does not by itself create the internal coupling described in the correct answer.

Adopt HTTP2 or gRPC for efficient service communication can improve performance and reduce overhead for service calls, but it does not eliminate the fundamental problem of synchronous tight coupling. Using efficient protocols is not the same as decoupling services and is not what you should avoid in this context.

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