TL;DR 🧠

REST is not always the best fit.

▪️ Need low-latency calls between services? → RPC

▪️ Need flexible data queries? → GraphQL

▪️ Need async, decoupled workflows? → Event/Messaging

Choose based on coupling, data needs, and runtime constraints — not hype. 🚀

🔸 REMOTE PROCEDURE CALL (RPC) 🛰

RPC = "call a function on another service as if it were local."

▪️ Typical stack: gRPC + protobuf

▪️ Fast, binary, low overhead 🔥

▪️ Strong contracts between services (IDLs / protobuf schemas)

▪️ Great for internal microservices talking to each other in real time

But…

▪️ Tight coupling between client and server interface

▪️ Harder across teams/orgs if you break compatibility

▪️ Not ideal for public/open APIs (tooling less universal than REST/HTTP+JSON)

When to use ✅

▪️ High-performance service-to-service calls inside your platform

▪️ You control both sides (same company, same versioning strategy)

🔸 GRAPHQL 🧬

GraphQL = "the client decides the shape of the response."

▪️ One endpoint, many query shapes

▪️ Ask only for what you need → less over/under-fetching 📦

▪️ Strongly typed schema = great DX for frontend

▪️ Can compose data from multiple backends in one request (BFF pattern)

But…

▪️ Can hide expensive queries behind “one request” (n+1 if not careful)

▪️ Caching is trickier than REST

▪️ Authorization rules can get complex per-field 🔐

When to use ✅

▪️ Public/partner/mobile/web APIs where consumers need flexibility

▪️ Aggregating multiple microservices into one client-facing API

🔸 MESSAGING / EVENT-DRIVEN API 📩

Event API = "don’t call me, I’ll tell you when something happens."

▪️ Producer publishes events (order.created, user.updated…)

▪️ Consumers react asynchronously

▪️ Loose coupling: producers don’t need to know who is listening 🙈

▪️ Scales naturally with new features (just add new consumers)

▪️ Great for audit, analytics, async workflows, integrations, CQRS, etc. 📊

But…

▪️ Harder mental model vs request/response

▪️ Delivery semantics, retries, idempotency, ordering… you need discipline

▪️ Debugging distributed flows can be harder

When to use ✅

▪️ Business events that trigger other processes (send email, update stock, bill customer)

▪️ Systems that must react in near real-time but not block the main request path

🔸 HOW DO I CHOOSE? 🤔

▪️ You’re in a microservices backend and you need speed → RPC

▪️ You’re building a public app/portal/mobile API → GraphQL

▪️ You’re building workflows/business reactions → Event/Messaging

➡️ You can (and often should) mix them in the same architecture. 💡

🔸 TAKEAWAYS 🏁

▪️ REST is a good default, but not the only tool

▪️ RPC = performance + control

▪️ GraphQL = flexibility + client power

▪️ Event API = decoupling + scalability

▪️ Picking the wrong style hurts long-term more than it hurts day 1 🧩

#api #rest #rpc #graphql #eventdriven #microservices #architecture

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