Base Images

When multiple components share common dependencies, you can create a base image to avoid duplication.

The Problem

Imagine you have several Node.js services that all need:

• The same Node.js version
• Common system packages (like curl for health checks)
• Shared utility libraries

Without a base image, you’d duplicate this setup in every Dockerfile.

The Solution: Base Component

Our microservices example has a base component:

cat base/Dockerfile

FROM node:22-alpine

# Install common dependencies
RUN apk add --no-cache curl

WORKDIR /app

# Copy shared utilities
COPY utils.js ./

# Set default environment
ENV NODE_ENV=development

This creates a foundation image with:

• Node.js 22 on Alpine Linux
• curl installed for health checks
• A shared utils.js module
• Common environment setup

The Base Embfile

The base component’s configuration:

cat base/Embfile.yml

description: Shared base image with common dependencies

tasks:
  info:
    description: Show base image info
    script: echo "Base image provides shared Node.js utilities"
    # Restrict this task to run only on the local machine (not inside a container).
    # By default, tasks can run on multiple executors (local, container).
    # Setting 'executors: [local]' means:
    # - The task runs on your host machine only
    # - Attempting to run with --executor=container will fail
    # - Useful for tasks that need host-level access or don't make sense in a container
    executors:
      - local

Using the Base Image

Other components inherit from this base. Here’s the worker’s Dockerfile:

cat worker/Dockerfile

ARG DOCKER_TAG=latest
FROM microservices/base:${DOCKER_TAG}

WORKDIR /app

COPY package.json ./
RUN npm install --production

COPY worker.js ./

CMD ["node", "worker.js"]

Notice FROM microservices/base:${DOCKER_TAG} - it inherits from our base image, using a build argument for the tag.

Benefits

1. Consistency - All services use the same Node.js version and utilities
2. Faster builds - Common layers are cached in the base image
3. Single update point - Update the base, rebuild dependents

Next Step

Continue to Dependencies to see how EMB tracks these relationships.