# AppSync
AppSync is a fully managed [[GraphQL|GraphQL]] service.

Notes:
- It can support real-time [[API]]s via GraphQL subscriptions.
- AppSync supports custom domains
- AppSync has a query editor built into the UI

## Resolvers
Resolvers attached to specific fields within your types in your schema. used to implement the state-changing operations for your query, mutation, and subscription field operations.

Runtimes:
- **`APPSYNC_JS`**: JavaScript
- **VTL**: Velocity Template Language.

## Data Sources
Where data is being pulled from.

- DynamoDB Table
- Amazon OpenSearch
- AWS [[_Lambda|Lambda Function]]
- [[HTTP]] Endpoint
- Amazon EventBridge
- Relational Database (RDS HTTP Endpoint)

## API Types
- **GraphQL APIs** - single API from multiple data sources
- **Merged APIs** - a collection of Graph APIs that act as one API
    - Useful if you have multiple teams that manage their own API but you want to treat all the APIs as a single API.
 
## Caching Options
- **None**: Self explanatory; no caching, resolvers will always fetch from data sources.
- **Full request caching**: Self explanatory; caches all requests.
- **Per-resolver caching**: specific operation or field defined in a resolver will return responses from the cache.
Caching isn't serverless; you must provision an on-demand instance.

# Authorisation
- API Key
- AWS IAM
- Cognito User Pools