fly-io

Fly.io Deployment & Management

Core Concepts

• Fly App: Named group of Machines (VMs) + config + networking + secrets belonging to one org
• Fly Machine: Fast-launching VM (sub-second start). Ephemeral root filesystem. Lifecycle: created -> started -> stopped -> destroyed
• Fly Volume: NVMe-backed persistent storage, 1:1 with a Machine, region-pinned, encrypted at rest by default
• Fly Proxy: Edge proxy handling TLS termination, load balancing, autostop/autostart, HTTP routing
• flyctl (fly): CLI for all Fly.io operations. Install: brew install flyctl or curl -L https://fly.io/install.sh | sh
• fly.toml: App configuration file. See references/fly-toml-config.md for complete reference

Quick Start Workflow

# 1. Create app + fly.toml
fly launch

# 2. Set secrets
fly secrets set DATABASE_URL=postgres://... SECRET_KEY=...

# 3. Deploy
fly deploy

# 4. Check status
fly status
fly logs

fly.toml Essentials

Minimal web app configuration:

app = 'my-app'
primary_region = 'ord'

[build]
  dockerfile = "Dockerfile"

[http_service]
  internal_port = 8080
  force_https = true
  auto_stop_machines = "stop"
  auto_start_machines = true
  min_machines_running = 1

  [http_service.concurrency]
    type = "requests"
    soft_limit = 200
    hard_limit = 250

[[vm]]
  memory = '512mb'
  cpu_kind = 'shared'
  cpus = 1

For the complete fly.toml reference with all sections, see references/fly-toml-config.md.

Machines Management

# Scale horizontally
fly scale count 3                          # 3 Machines in primary region
fly scale count 3 --region ord,iad         # Across regions

# Scale vertically
fly scale vm performance-1x --vm-memory 2048

# Direct Machine control
fly machine run <image> --region ord
fly machine clone <machine-id> --region iad
fly machine update <machine-id> --vm-memory 512
fly machine stop <machine-id>
fly machine start <machine-id>
fly machine destroy <machine-id>

Machine sizes: shared-cpu-1x (256MB default), shared-cpu-2x, shared-cpu-4x, shared-cpu-8x, performance-1x through performance-16x. GPU options: a10, l40s, a100-pcie-40gb, a100-sxm4-80gb.

Volumes

fly volumes create mydata --region ord --size 10   # 10GB
fly volumes list
fly volumes extend <vol-id> --size 20              # Extend to 20GB (cannot shrink)
fly volumes snapshots list <vol-id>
fly volumes fork <vol-id>                          # Copy a volume

Configure in fly.toml:

[mounts]
  source = "mydata"
  destination = "/data"
  initial_size = "10gb"
  auto_extend_size_threshold = 80
  auto_extend_size_increment = "1GB"
  auto_extend_size_limit = "50GB"

Critical: Volumes are 1:1 with Machines, region-pinned, no automatic replication. Always provision at least 2 Machines with volumes for redundancy. Your app must handle data replication between volumes.

Secrets

fly secrets set KEY=value OTHER_KEY=other_value
fly secrets set KEY=value --stage               # Stage without restarting
fly secrets deploy                               # Deploy staged secrets
fly secrets list                                 # Names only, no values
fly secrets unset KEY OTHER_KEY

Secrets are encrypted at rest, injected as env vars at boot. Use [[files]] in fly.toml to mount secrets as files (value must be base64-encoded):

[[files]]
  guest_path = "/etc/ssl/private/key.pem"
  secret_name = "TLS_PRIVATE_KEY"

Logs

fly logs                                     # Continuous tail (default, streams indefinitely)
fly logs --no-tail                           # Output recent logs once and exit
fly logs --machine <machine-id>              # Filter to a specific machine
fly logs --machine <machine-id> --no-tail    # Recent logs for one machine, then exit
fly logs --region iad                        # Filter by region
fly logs --json                              # JSON-formatted output

Important: flyctl logs does NOT support -n, --tail <count>, or --lines flags. To limit output, pipe through standard tools:

fly logs --no-tail | head -50                # Last 50 lines
fly logs --no-tail | tail -20                # Most recent 20 lines
fly logs --machine <id> --no-tail | grep -i error   # Search for errors

Available flags:

Flag	Description
--no-tail (-n)	Output logs once and exit (do not stream)
--machine <id>	Filter to a specific machine ID
--region <code>	Filter by region (e.g., iad, ord)
--json (-j)	JSON output format
--app <name> (-a)	Specify app name (if not in fly.toml directory)

Networking

For detailed networking patterns (public services, private networking, Flycast, custom domains, DNS), see references/networking.md.

Quick Reference

fly ips list                                 # List allocated IPs
fly ips allocate-v6                          # Dedicated IPv6 (free)
fly ips allocate-v4 --shared                 # Shared IPv4 (free)
fly ips allocate-v4                          # Dedicated IPv4 (paid)
fly certs create mydomain.com                # Add custom domain + TLS cert

Private networking: All apps in an org share a WireGuard mesh (6PN). Use <appname>.internal DNS for inter-app communication. Bind to fly-local-6pn or [::]:port to accept private connections.

Health Checks

Service-level checks affect Fly Proxy routing. Top-level [checks] are for monitoring only.

# In [http_service] or [[services]]
[[http_service.checks]]
  grace_period = "10s"
  interval = "30s"
  timeout = "5s"
  method = "GET"
  path = "/health"

# Top-level (monitoring, no routing impact)
[checks.my_check]
  type = "http"
  port = 8080
  path = "/health"
  interval = "30s"
  timeout = "5s"

Autoscaling

Autostop/autostart (Fly Proxy-based, for web services):

[http_service]
  auto_stop_machines = "stop"      # "off", "stop", or "suspend"
  auto_start_machines = true
  min_machines_running = 1

  [http_service.concurrency]
    type = "requests"
    soft_limit = 200               # Used for excess capacity calculation

Metrics-based autoscaling: Deploy the autoscaler app in your org. It polls Prometheus metrics and creates/destroys Machines. See Fly.io docs for setup.

Deployment Strategies

[deploy]
  strategy = "rolling"              # "rolling" (default), "immediate", "canary", "bluegreen"
  max_unavailable = 0.33            # For rolling: fraction or integer
  release_command = "bin/migrate"   # One-off command before deploy (e.g., DB migrations)

• rolling: One-by-one replacement (default)
• immediate: All at once, skip health check waits
• canary: Boot one Machine, verify health, then rolling (no volumes)
• bluegreen: Boot new set alongside old, migrate traffic after health checks (requires health checks, no volumes)

CI/CD with GitHub Actions

For complete CI/CD setup including deploy tokens, review apps, and multi-app deploys, see references/cicd-github-actions.md.

Quick setup:

# .github/workflows/fly.yml
name: Fly Deploy
on:
  push:
    branches: [main]
jobs:
  deploy:
    runs-on: ubuntu-latest
    concurrency: deploy-group
    steps:
      - uses: actions/checkout@v4
      - uses: superfly/flyctl-actions/setup-flyctl@master
      - run: flyctl deploy --remote-only
        env:
          FLY_API_TOKEN: ${{ secrets.FLY_API_TOKEN }}

Generate deploy token: fly tokens create deploy -x 999999h

Databases & Storage

For detailed database and storage patterns, see references/databases-storage.md.

• Managed Postgres: fly mpg create -- fully managed, automated backups
• Tigris Object Storage: S3-compatible, fly storage create
• Upstash Redis: Managed Redis, fly redis create

Production Checklist

1. Security: Enable SSO, use secrets for sensitive data, release unnecessary public IPs from private apps, use Flycast for internal services
2. Performance: Use performance CPUs for production web apps, right-size memory, enable swap (swap_size_mb) for spike absorption
3. Availability: Run 2+ Machines (ideally across regions), configure autostop/autostart, set up health checks
4. Networking: Set up custom domain + TLS cert, consider dedicated IPv4 if needed
5. Monitoring: Configure Prometheus metrics export, set up Sentry, export logs to external service
6. CI/CD: Deploy via GitHub Actions with deploy tokens, set up review app previews

Process Groups

Run multiple processes in one app (e.g., web + worker):

[processes]
  web = "bin/rails server -b 0.0.0.0 -p 8080"
  worker = "bin/sidekiq"

[http_service]
  internal_port = 8080
  processes = ["web"]

[[vm]]
  processes = ["web"]
  memory = "1gb"

[[vm]]
  processes = ["worker"]
  memory = "512mb"

Useful Commands Cheat Sheet

Command	Description
fly launch	Create app + fly.toml
fly deploy	Build and deploy
fly deploy --remote-only	Build on Fly.io builders
fly status	App and Machine status
fly logs	Tail live logs (continuous stream)
fly logs --no-tail	Output recent logs once and exit
fly logs --machine <id>	Filter logs to specific machine
fly logs --machine <id> --no-tail	Recent logs for one machine, then exit
fly logs --region iad	Filter logs by region
fly logs --json	Output logs in JSON format
fly ssh console -s	SSH into a Machine (select)
fly proxy 5432:5432	Proxy local port to app
fly dashboard	Open web dashboard
fly scale show	Show current scaling
fly checks list	View health check status
fly releases	List releases
fly config show	Show current fly.toml
fly apps restart	Restart all Machines