Autoscaling on Fly.io

Why pay for servers that are just sitting there eating Cheetos? Your app should scale up when it's busy and scale down when it's not. Autoscaling on Fly.io means you only run what you need, when you need it. It's your accountant's favorite feature.

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Autostop and Autostart

Autostop/Autostart: The "Only Pay for What You Use" Button

A user calls your app, your Machines wake up. Like ... really, really fast. No traffic? Machines go back to sleep. No CPU or RAM charges while stopped. It's easy to configure this behavior to cover exactly what your project needs.

  • Wake up in milliseconds when requests arrive
  • Stop automatically during idle periods
  • Zero CPU/RAM charges when stopped
  • Set minimum Machines to keep warm
  • Perfect for sporadic traffic patterns
  • Enabled by default for new apps

Metrics-Based Autoscaling: Because Queue Depth > Request Count

Sometimes "number of HTTP requests" isn't the right metric. Got background workers chomping through a job queue? Temporal workflows piling up? Scale based on what actually matters to your app: queue depth, pending work, custom metrics from Prometheus, whatever keeps you up at night.

Scale based on queue depth, pending jobs, or custom metrics
Pull metrics from Prometheus or Temporal
Write scaling rules with expressions and arithmetic
Create or destroy Machines dynamically
Scale multiple apps with common naming patterns
Metrics-Based Autoscaling

What Even is This Magic?

Fly Proxy sits at the edge and watches traffic. When a request shows up for a sleeping Machine, the proxy wakes it up faster than you can say "cold start problem." Machines boot in milliseconds, handle the request, and go back to sleep when things quiet down. You configure the behavior, we handle the orchestration.

Fly Proxy detects incoming traffic and wakes Machines instantly
Configure stop/start behavior in your fly.toml
Set minimum Machines running to avoid cold starts
Machines only get charged when they're actually running
Read the autoscaling docs

Read the Docs

Autoscaling Overview

Learn about the different autoscaling strategies on Fly.io

Autostop/Autostart

Configure automatic Machine stopping and starting based on traffic

Autoscale by Metric

Scale based on custom metrics like queue depth or pending work

Configuration Reference

See all the autoscaling settings in fly.toml

Stop Paying for Idle Servers

Get Started with Autoscaling

Whatever happened to the promise of paying only for what you use in cloud infra? With Fly.io autoscaling, that's actually true. Machines wake up when there's work to do and go back to sleep when there isn't. No babysitting required.

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