Imported from jeremylongshore/tons-of-skills-marketplace (skills/.curated/flyio-cost-tuning/SKILL.md). Install upstream with npx skills add jeremylongshore/tons-of-skills-marketplace --skill flyio-cost-tuning. Copyright stays with the author (MIT).

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.

Prerequisites

• Current contract/billing data reviewed by the account owner, aggregate resource usage, and a named cost owner.
• Availability, latency, durability, and retention requirements that constrain autoscaling and volume decisions.
• Synthetic staging load and a rollback plan for each cost-control change.

Output

Produce a cost-control receipt with measurement window, aggregate usage, approved setting change, expected effect, owner, verification date, and rollback result. Never include tokens, customer data, or internal billing details.

Error Handling

• Do not remove volumes or capacity without confirmed retention, backup, and recovery requirements.
• Revert a cost change that breaches availability, latency, or data-durability thresholds.
• Quarantine unexpected resource changes for review rather than applying bulk cleanup.

Examples

Apply a suspend policy to a fictional staging app, compare aggregate idle cost and cold-start health, and roll back when a synthetic health check breaches the agreed latency threshold. Do not delete any volume as part of an exploratory test.

Pricing Quick Reference

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

• Fly.io Pricing
• Auto Stop/Start

Next Steps

For architecture design, see flyio-reference-architecture.