Fly.io Cost Tuning Skill

Fly.io Cost Tuning

Overview

Fly.io charges per-second for running machines plus storage. Key levers: auto-stop idle machines, suspend instead of stop, right-size VMs, and clean up unused volumes.

Pricing Quick Reference

| Resource | Free Tier | Cost | |----------|-----------|------| | shared-cpu-1x (256mb) | 3 VMs free | ~$1.94/month each | | shared-cpu-1x (512mb) | included | ~$3.88/month | | shared-cpu-2x (1gb) | - | ~$11.62/month | | Volumes | 3GB free | $0.15/GB/month | | Bandwidth | 100GB free | $0.02/GB after | | IPv4 | 1 free per org | $2/month each |

Instructions

Strategy 1: Auto-Stop Idle Machines

# fly.toml — stop machines when no traffic
[http_service]
  auto_stop_machines = "stop"     # Full stop (cheapest, ~5s cold start)
  auto_start_machines = true
  min_machines_running = 0        # Allow all machines to stop
  # Use min_machines_running = 1 only for production apps

Strategy 2: Suspend for Faster Resume

# Suspend keeps memory state — resumes in ~100ms but costs ~$0.50/month
[http_service]
  auto_stop_machines = "suspend"

Strategy 3: Audit and Clean Up

# List all apps and their machine counts
fly apps list

# Find idle/stopped machines
fly machine list -a my-app --json | jq '.[] | select(.state != "started") | {id, state, region}'

# Destroy unused apps
fly apps destroy old-app --yes

# List and delete orphaned volumes
fly volumes list -a my-app
fly volumes destroy vol_xxx

Strategy 4: Right-Size VMs

# Check memory usage to see if oversized
fly ssh console -a my-app -C "cat /proc/meminfo | head -3"

# Downgrade if using <50% of allocated memory
fly scale vm shared-cpu-1x --memory 256 -a my-app

Cost Monitoring

# Check current month's usage
fly billing  # Shows org-level billing

# Estimate per-app cost
fly scale show -a my-app  # See VM count and size

Resources

Next Steps

For architecture design, see flyio-reference-architecture.

Agent Skills: Fly.io Cost Tuning

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