Scale to zero
Idle apps sleep at 0 CPU and RAM, and wake on the first request.
On the Free plan, an app that isn't receiving traffic sleeps — its container stops, using 0 CPU and 0 RAM — rather than sitting idle and billing for nothing happening.
Waking up
The first request to a sleeping app wakes it. That request waits briefly — typically a few hundred milliseconds — while the container starts back up, then goes through normally. Every request after that is served immediately, for as long as the app stays active.
What counts as activity
Incoming HTTP requests keep an app awake and reset its idle timer. An app that's genuinely idle — no requests, not a background worker doing its own thing — is what goes to sleep.
When this isn't what you want
Long-running processes that don't answer HTTP requests — a bot connected to WhatsApp or Telegram, a queue worker, anything that needs to stay connected regardless of inbound traffic — don't fit this model. There's no incoming request to keep them "awake" by the usual definition, so they'd be treated as idle and stopped.
Pro and Team apps are always-on and never sleep — this is the right plan for anything that needs to run continuously. See Deploying → Node.js for more on this.
Why this is safe
DockHosting only sleeps an app it's confident is actually idle — an app is never put to sleep mid-request, and the wake path is designed to be fast enough that a real user rarely notices it happened at all.