AWS’s serverless WebSocket API against a realtime platform: per-operation billing, and everything a channel needs beyond delivery.
AppSync Events, launched in late 2024, is AWS’s purpose-built pub/sub over WebSocket: ephemeral channels, per-namespace JavaScript handlers, IAM and Cognito auth, and pure pay-per-use pricing. It is a credible primitive. The comparison is what comes built in versus what its handlers and your DynamoDB tables have to provide.
When Foony fits
Presence, history, and recovery exist. AppSync Events has none of the three: channels are ephemeral, a disconnected client silently misses events, and who-is-online is a DynamoDB table you maintain from handlers.
Documented delivery guarantees. AWS states none for Events: no ordering promise, no subscriber-side redelivery.
Fan-out pricing that doesn’t meter pings. AppSync bills every operation: each publish, each delivery per subscriber per 5 KB, each handler invocation, each connect, each subscribe, and each ping frame.
Connections without a daily rebuild: AppSync WebSockets last at most 24 hours.
A free tier that stays free. The AppSync free tier expires 12 months after signup.
When AWS AppSync Events fits
You are all-in on AWS: IAM and Cognito auth on the socket, handlers that call Lambda, DynamoDB, Bedrock, and EventBridge directly, one compliance boundary.
Very low cost at modest fan-out: AWS’s own worked example runs a million-connection month for about $13.
Server-side channel logic without servers: OnPublish and OnSubscribe handlers filter, transform, and gate in-path.
Features
Foony
AWS AppSync Events
Presence
Built in, with automatic re-entry on reconnect
None, DIY via handlers and your own store
History
Per-prefix channel rules, up to 30 days
None, channels are ephemeral
Delivery
Effectively exactly once (idempotent publish, client dedup)
No documented guarantee
Connection lifetime
Held open with keep-alive pings
24 hours maximum
In-path logic
Not a feature, your backend publishes what it wants delivered
JS handlers per namespace with AWS data sources
Limits and pricing
Foony
AWS AppSync Events
Pricing model
Per message, in and out
$1 per million operations, where publishes, deliveries (per 5 KB), handlers, connects, subscribes, and pings are all operations, plus $0.08 per million connection minutes