/firebase-app-hosting-basics

App Hosting Configuration (apphosting.yaml)

The apphosting.yaml file is the source of truth for your backend's configuration. It must be located in the root of your app's directory (or the specific root directory if using a monorepo).

File Structure

# apphosting.yaml

# Cloud Run service configuration
runConfig:
  cpu: 1
  memoryMiB: 512
  minInstances: 0
  maxInstances: 100
  concurrency: 80

# Environment variables
env:
  - variable: STORAGE_BUCKET
    value: mybucket.app
    availability:
      - BUILD
      - RUNTIME
  - variable: API_KEY
    secret: myApiKeySecret

runConfig

Controls the resources allocated to the Cloud Run service that serves your app.

• cpu: Number of vCPUs. Note: If < 1, concurrency MUST be set to 1.
• memoryMiB: RAM in MiB (128 to 32768).
• minInstances: Minimum containers to keep warm (default 0). Set to >= 1 to avoid cold starts.
• maxInstances: Maximum scaling limit (default 100).
• concurrency: Max concurrent requests per instance (default 80).

Resource Constraints

• CPU vs Memory: Higher memory often requires higher CPU.

  • 4GiB RAM -> Needs >= 2 vCPU

  • 8GiB RAM -> Needs >= 4 vCPU

env (Environment Variables)

Defines environment variables available during build and/or runtime.

• variable: The name of the env var (e.g., NEXT_PUBLIC_API_URL).
• value: A literal string value.
• secret: The name of a secret in Cloud Secret Manager. use npx -y firebase-tools@latest apphosting:secrets:set to create these.
• availability: Where the variable is needed.
  • BUILD: Available during the npm run build process.
  • RUNTIME: Available when the app is serving requests.
  • Defaults to both if not specified.