Real time with AppSync and DynamoDB Streams

Comments

• AppSync manages WebSocket subscriptions for you. If you need full control over the connection, API Gateway WebSocket is the alternative.
• DynamoDB Streams delivers each table change in order, so there is no need to poll the database periodically.
• Authenticate connections with Amazon Cognito or another identity provider. Without a valid token, AppSync does not open subscriptions.
• Send only what changed in each event. Resending the full state on every change consumes bandwidth and raises cost.

Information flow

1. AWS AppSync

   The user sends a GraphQL mutation to AppSync.

2. Amazon DynamoDB

   AppSync writes the change to the DynamoDB table.

3. DynamoDB Streams + AWS Lambda

   DynamoDB Streams emits the change and a Lambda function receives it.

4. AWS Lambda

   Lambda sends the event back to AppSync.

5. AWS AppSync

   AppSync pushes the event to subscribed clients over WebSocket.