Building Images

FTL provides a streamlined way to build Docker images for your services. This guide covers the build process and available options.

Basic Usage

To build images for all services defined in your ftl.yaml:

ftl build

Image Handling in FTL

FTL offers two ways to handle Docker images:

1. Direct SSH Transfer (Default)

When no image field is specified in your service configuration, FTL will:

• Build the image locally
• Transfer it directly to your server via SSH
• Use its own layer caching algorithm to optimize transfers
• Only transfer layers that haven't been previously sent to the server

services:
  - name: web
    build:
      context: .
      dockerfile: Dockerfile

TIP

This method is simpler as it doesn't require registry configuration and credentials management.

2. Registry-based Deployment

When you specify the image field, FTL will:

• Build and tag the image locally
• Push it to the specified registry
• Pull the image on the server during deployment
• Require registry authentication during server setup
• Currently support only username/password authentication

services:
  - name: web
    image: registry.example.com/my-app:latest
    build:
      context: .
      dockerfile: Dockerfile

WARNING

Currently, FTL only supports registries with username/password authentication. Token-based authentication will fail.

Build Options

Command Line Flags

# Skip pushing images to the registry (only applies when using registry-based deployment)
ftl build --skip-push

Understanding Docker Builds

Build Context

The build context is the set of files located in the specified context path. Docker sends this context to the daemon during the build. Keep your context clean to ensure faster builds:

• Use .dockerignore to exclude unnecessary files
• Keep build context as small as possible
• Place Dockerfile in a clean directory if needed

Layer Caching

Docker uses a layer cache to speed up builds. Understanding how it works can significantly improve build times:

1. Layer Order Matters

   • Put infrequently changed commands early in Dockerfile
   • Place frequently changed commands (like copying source code) later

2. Cache Busting

   • Adding/modifying files invalidates cache for that layer and all following layers
   • Changing a command invalidates cache for that layer and all following layers

Multi-stage Builds

Multi-stage builds help create smaller production images:

# Build stage
FROM node:18 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build

# Production stage
FROM node:18-slim
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY package*.json ./
RUN npm install --production
CMD ["npm", "start"]

Benefits:

• Smaller final image size
• Separation of build and runtime dependencies
• Better security by excluding build tools

Best Practices

1. Choose the Right Deployment Method

   • Use direct SSH transfer for simpler setups
   • Use registry-based deployment when:
     • You need image versioning
     • Multiple servers need the same image
     • You require image scanning/signing

2. Registry Configuration

   • Use username/password authentication
   • Avoid token-based registries (currently unsupported)
   • Consider registry proximity to your servers

3. Optimize Dockerfiles

   • Use multi-stage builds
   • Minimize layer count
   • Order commands by change frequency
   • Use specific base image tags

4. Image Tags

   • Use meaningful tags
   • Consider versioning strategy
   • Document tagging conventions

5. Build Performance

   • Leverage Docker layer caching
   • Use .dockerignore effectively
   • Keep build context minimal

6. Security

   • Use official base images
   • Keep base images updated
   • Scan images for vulnerabilities
   • Don't store secrets in images

Common Docker Issues

Build Performance

If builds are slow:

• Check build context size
• Optimize layer caching
• Use .dockerignore appropriately
• Consider multi-stage builds

Image Size

To reduce image size:

• Use multi-stage builds
• Choose appropriate base images
• Remove unnecessary files
• Combine RUN commands

Cache Issues

If cache isn't working effectively:

• Check command ordering in Dockerfile
• Verify file changes aren't invalidating cache
• Use appropriate COPY commands

Common Issues

Registry Authentication

If using registry-based deployment:

• Ensure registry supports username/password authentication
• Have credentials ready during server setup
• Verify registry URL is correct
• Check network connectivity to registry

Next Steps

After building your images:

1. Deploy your application
2. Learn about Zero-downtime Deployments
3. Configure Health Checks

WARNING

Always test builds in a development environment before building for production.

Reference

• Configuration Reference
• Troubleshooting Guide
• Docker Documentation