flycost

Cost estimation tool for Fly.io applications

flycost analyzes your fly.toml configuration files and estimates monthly costs for compute, storage, bandwidth, and IP addresses. Similar to infracost, but specifically for Fly.io.

Quick Start

Install (Recommended)

macOS/Linux:

curl -sSLf https://github.com/gordonmurray/flycost/releases/latest/download/install.sh | bash

Manual download:

# Replace VERSION with latest release (e.g., v1.0.0)
OS=$(uname -s | tr '[:upper:]' '[:lower:]')
ARCH=$(uname -m | sed 's/x86_64/amd64/; s/aarch64/arm64/')
wget "https://github.com/gordonmurray/flycost/releases/download/VERSION/flycost_${OS}_${ARCH}.tar.gz"
tar -xzf flycost_*.tar.gz
sudo mv flycost /usr/local/bin/

Build from Source

git clone https://github.com/gordonmurray/flycost.git
cd flycost
go build -o flycost ./cmd/flycost

Usage

Basic Usage

# Scan current directory for fly.toml files
flycost

# Scan specific directory
flycost -root ./my-apps

# Output as JSON
flycost -format json

Example Output

Kind        Monthly  App           Note                     File
----------- -------  ------------- ------------------------ -----------
compute     $  1.94  user-service  shared-cpu-1x 1024MB     express-microservice.toml
volume      $  1.50  user-service  10 GB (assumed)          express-microservice.toml
bandwidth   $  2.00  user-service  lhr 100 GB               express-microservice.toml
ip          $  2.00  user-service  1 IPv4 (assumed)         express-microservice.toml
compute     $ 82.12  ml-inference-api performance-1x 16384MB   ml-worker.toml
volume      $  1.50  ml-inference-api 10 GB (assumed)          ml-worker.toml
bandwidth   $  2.00  ml-inference-api iad 100 GB               ml-worker.toml
ip          $  2.00  ml-inference-api 1 IPv4 (assumed)         ml-worker.toml
compute     $  3.88  my-rails-api  shared-cpu-2x 2048MB     rails-api.toml
compute     $  1.94  my-rails-api  shared-cpu-1x 1024MB     rails-api.toml
volume      $  1.50  my-rails-api  10 GB (assumed)          rails-api.toml
bandwidth   $  2.00  my-rails-api  cdg 100 GB               rails-api.toml
ip          $  2.00  my-rails-api  1 IPv4 (assumed)         rails-api.toml
compute     $  1.94  my-react-app  shared-cpu-1x 256MB      react-spa.toml
bandwidth   $  2.00  my-react-app  iad 100 GB               react-spa.toml
ip          $  2.00  my-react-app  1 IPv4 (assumed)         react-spa.toml

TOTAL: $112.32 / mo

Example Applications

The examples/ folder contains realistic fly.toml configurations:

• react-spa.toml - Static React app ($5.94/mo)
• express-microservice.toml - Node.js API with file storage ($7.44/mo)
• rails-api.toml - Multi-instance Rails API with volumes ($13.32/mo)
• ml-worker.toml - High-performance ML inference service ($87.62/mo)

Configuration

Create .flycost.yml in your project root to customize cost assumptions:

root: "."
assumptions:
  egress_gb_per_app: 100        # Monthly bandwidth usage
  ipv4_per_app: 1               # Number of IPv4 addresses
  default_volume_gb: 10         # Default volume size when mounts exist
  postgres_monthly_usd: 0       # Add-on Postgres cost
bandwidth_rates:
  default: 0.02                 # $/GB for unknown regions
  iad: 0.02                     # $/GB for US East
  cdg: 0.02                     # $/GB for Europe

Supported fly.toml Features

• Compute: VM sizes, CPU types (shared/performance), memory
• Storage: Volume mounts (estimates size if not specified)
• Networking: Bandwidth based on primary region
• IP Addresses: IPv4 allocation costs

Sample fly.toml Formats

flycost supports both standard TOML array syntax and Fly.io's newer single-section syntax:

Array syntax ([[vm]], [[mounts]]):

app = "my-web-app"
primary_region = "iad"

[[vm]]
cpus = 2
cpu_kind = "shared"
memory_mb = 2048

[[mounts]]
source = "data_volume"
destination = "/data"

Single section syntax ([mounts]):

app = "user-service"
primary_region = "lhr"

[[vm]]
cpus = 1
cpu_kind = "shared"
memory_mb = 1024

[mounts]
source = "uploads"
destination = "/app/uploads"

Pricing

Built-in pricing is based on Fly.io's public pricing:

Compute (Base VM costs with 256MB RAM)

• Shared CPU: $1.94/mo per vCPU
• Performance CPU: $31/mo per vCPU
• Memory: $4.26/mo per GB above base allocation

Infrastructure

• Volumes: $0.15/mo per GB
• IPv4: $2/mo per address
• Bandwidth:
  • North America/Europe: $0.02/mo per GB
  • Asia Pacific: $0.04/mo per GB

Updating Pricing

Pricing data is stored in pkg/pricing/pricing.json. To update:

1. Check current rates at fly.io/docs/about/pricing
2. Edit pkg/pricing/pricing.json:

   {
     "ram_per_gb_month": 4.26,
     "volume_gb_month": 0.15,
     "egress_gb_by_region": {
       "default": 0.02,
       "iad": 0.02,     // North America
       "cdg": 0.02,     // Europe
       "nrt": 0.04,     // Asia Pacific
       "syd": 0.04      // Oceania
     },
     "vm_preset_month": {
       "shared-cpu-1x": 1.94,
       "performance-1x": 31.0
     }
   }

3. Rebuild: go build -o flycost ./cmd/flycost

Prices are estimates. Always verify with fly.io/docs/about/pricing for official rates.

Command Line Options

Usage: flycost [options]

Options:
  -root string
        Directory to scan for fly.toml files (default: current directory)
  -format string
        Output format: table|json (default: "table")
  -config string
        Path to custom .flycost.yml config file

Integration

CI/CD Usage

# GitHub Actions example
- name: Estimate Fly.io costs
  run: |
    curl -sSLf https://github.com/gordonmurray/flycost/releases/latest/download/install.sh | bash
    flycost -format json > costs.json

Shell Integration

# Add to your deployment script
echo "💰 Estimating costs..."
flycost
echo "Deploying to Fly.io..."
fly deploy

Contributing

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request