A WebSocket demo takes an afternoon. Keeping thousands of connections correct through deploys, reconnects, phones changing networks and a second server takes ongoing work. Many "realtime" features are better served by a 15-second poll or a server-sent event stream. A feature-by-feature guide, and the list of what you take on when the answer really is WebSockets.
Every platform now makes the first WebSocket easy: Vercel Functions since October 2026, API Gateway and AppSync on AWS, Cloudflare, and every container host. That makes the decision more important, not less. The socket is the cheap part. The expensive part is everything that has to stay correct while thousands of them come and go.
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Reconnects with backoff and jitter, so a deploy or a blip doesn't bring every client back in the same second.
Catch-up: messages sent while a client was disconnected need sequence numbers and a store to replay from.
Fan-out across servers: a message arriving on one instance has to reach sockets held by the others, which means Redis, a managed pub/sub, or a service built for it.
Authorization over time: a connection opened at 9am may outlive the session, role or account that opened it.
Deploys: old connections keep running old code until they close, or you close them and absorb the reconnect storm.
Phones: networks change, apps are suspended, and a socket that looks open often isn't. Heartbeats and timeouts are yours.
Ordering and duplicates: at-least-once delivery means handlers must be idempotent.
Observability: request logs don't show a connection that's been open for 20 minutes. You need connection counts, message rates and reconnect rates.
Load testing: the failure is rarely steady state. It is 10,000 clients reconnecting at once after a deploy.
Managed realtime services (Ably, Pusher, Liveblocks, Firebase, and AWS AppSync Events) handle reconnection, fan-out, presence and often history as features. They charge per message or connection, which looks expensive next to a socket you host until you price the engineering time for the list above. For collaborative editing in particular, buying is usually right.
We look at what you run, where it breaks and what it costs, and tell you whether to fix it, simplify it or hand part of it to a managed service.
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Or keep reading
WebSockets on Vercel Functions Are Generally Available: The Limits, the Bill, and What You Still Build
Since October 20, 2026, Vercel Functions serve WebSocket connections on every plan, with Express, Hono, Socket.IO, Bun, FastAPI and Next.js. Connections close at the function's maximum duration (300 seconds on Hobby, up to 800 on Pro), each is pinned to one instance, and memory is billed while any connection is open. What that means for your design and your bill.
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Realtime Pricing Compared: Vercel WebSockets, API Gateway WebSocket APIs and AppSync Events
The same workload priced three ways: 1,000 users connected through the workday, 48 million messages a month. On AWS, API Gateway and AppSync Events charge about $1 per million messages and differ mostly in connection minutes and in who does the fan-out. Vercel charges almost nothing per message but bills memory for every instance holding connections. Where each one wins.
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As of November 2, 2026. Provided as is, for general information, and accurate to the best of our knowledge on the date shown. Not legal, compliance, tax, financial or other professional advice. Prices, limits and vendor services change; check current vendor documentation before relying on anything here. Terms of use.