What is AWS AppSync?

Start with the GraphQL contract

A GraphQL schema defines types, queries, mutations, and subscriptions. Clients ask for fields from that contract, while resolvers determine how each field is read or changed in the underlying systems.

The schema is an application boundary, not a direct copy of database tables. Design it around stable domain operations, validate input, and prevent consumers from depending on storage details that need to evolve.

Choose direct and function-backed resolvers

AppSync can integrate directly with supported data sources or call Lambda and HTTP services. Direct integration can remove code for straightforward reads and writes, while a function or pipeline resolver can enforce more complex business behavior.

Keep authorization and invariants visible. Fewer functions do not automatically mean simpler ownership if resolver logic becomes fragmented or difficult to test.

Plan real-time delivery and offline behavior

GraphQL subscriptions can publish updates to connected clients after mutations. Event APIs can provide managed WebSocket channels for publish-and-subscribe use cases without requiring a GraphQL schema.

Real-time delivery needs connection authorization, channel or subscription boundaries, disconnect handling, client resynchronization, and an authoritative data source. A pushed event should not be the only copy of important state.

Control authorization, query work, and caching

AppSync supports several authorization modes, and field-level rules may be needed when one schema serves different identities. Limit query depth, complexity, result size, and expensive resolver paths before public traffic discovers them.

Use caching only where freshness rules are clear. Observe resolver latency, errors, authorization failures, throttling, and downstream capacity so a flexible client query cannot become uncontrolled backend work.