Used For

• +**Your app takes 3 seconds to load in Europe from your US server** → Users worldwide get sub-100ms load times from the nearest edge server
• +**You're paying $300/month for idle Heroku dynos that sit unused 80% of the time** → Machines auto-pause when idle, you pay $0.15/GB for storage instead of full compute
• +**Your weekend side project got featured on Hacker News and crashed** → Auto-scales to 10,000+ instances in seconds without you waking up to fix it
• +Machines start in milliseconds like serverless functions - but they're full Linux VMs that can run databases and stateful apps

Best For

• >Your SaaS is slow for users outside the US and you need global speed yesterday
• >Hit the Heroku pricing wall but AWS feels like learning rocket science
• >Building an MVP and want worldwide deployment without hiring a DevOps team

Not For

• -Non-technical founders who want point-and-click deployment — this requires Docker knowledge and CLI comfort
• -Enterprise teams needing Terraform and compliance — Fly skips infrastructure-as-code for simplicity
• -Anyone building stateful apps with complex data — volumes don't auto-replicate between regions, you handle that yourself

Pairs With

• *GitHub Actions (triggers deploys when you push code, though many just run `fly deploy` manually)
• *PostgreSQL (managed Fly Postgres or external, but you handle replication between regions)
• *Docker (required - Fly deploys your containers, not source code like Vercel)
• *Upstash Redis (for caching, though watch the data transfer costs between services)
• *Sentry (to catch errors across all your global instances)
• *Stripe (common for SaaS apps that need global payment processing)

The Catch

• !Data transfer fees add up fast at $0.02/GB — one user hit $150 surprise bills moving 10TB between regions
• !Volumes are tied to single machines with no auto-sync, so your Postgres clustering breaks if you're not careful
• !Cold starts take 30-60 seconds during traffic spikes, causing 503 errors while machines wake up

Bottom Line

Deploys your app globally in 5 minutes instead of spending weeks configuring AWS regions.