How to migrate Docker Compose config to Kamal with two Dockerfiles for frontend and backend apps

[tom-spalding]

Hello, I have the following docker-compose.yml script I'm migrating to Kamal deploy.yml. I'm having difficulty finding the equivalent way to set up build: ./frontend & build: ./backend like Docker Compose. Has anyone ran into this before making a frontend and backend app deploy with Kamal? Both apps are in one Git repo.

For completeness I'm including the db setup, but mostly I'm looking at the web and api under services in docker-compose.yml.

docker-compose.yml:

name: ACatApp
services:
  web:
    build: ./frontend # <------
    stdin_open: true
    tty: true
    depends_on:
      - api
    ports:
      - 5000:5000
    image: cat-app-web
    networks:
      - cat-network

  api:
    build: ./backend # <------
    stdin_open: true
    tty: true
    ports:
      - 5001:5001
    image: cat-app-api
    depends_on:
      - db
    networks:
      - cat-network

  db:
    image: mongo
    restart: always
    volumes:
      - cat-storage:/data/db
      - ./backend/mongo-init.js:/docker-entrypoint-initdb.d/mongo-init.js
    networks:
      - cat-network
    environment:
      MONGO_INITDB_DATABASE: cats

  mongo-express:
    image: mongo-express
    restart: always
    ports:
      - 8081:8081
    environment:
      ME_CONFIG_BASICAUTH_USERNAME: catuser
      ME_CONFIG_BASICAUTH_PASSWORD: catpass
      ME_CONFIG_HEALTH_CHECK_PATH: /up
      ME_CONFIG_MONGODB_URL: mongodb://db:27017/
      ME_CONFIG_SITE_BASEURL: /admin
    networks:
      - cat-network

networks:
  cat-network:

volumes:
  cat-storage:
    external: true
    name: cat-storage

Please forgive the find-and-replace cat placeholders.

The Docker Compose build option allows me to have two Dockerfiles for the frontend and backend apps. For historical reasons they weren't built at the same time.

backend/Dockerfile:

# syntax=docker/dockerfile:1
# check=error=true

# https://hub.docker.com/_/node/
FROM docker.io/library/node:24-alpine

WORKDIR /api

COPY package.json ./
COPY package-lock.json ./

RUN npm install

COPY . .

ENV NODE_ENV=production

EXPOSE 5001
CMD ["node", "server.js", "-p", "5001"]

frontend/Dockerfile:

# syntax=docker/dockerfile:1
# check=error=true

# https://hub.docker.com/_/node/
FROM docker.io/library/node:24-alpine

WORKDIR /web

ENV PATH=/web/node_modules/.bin:$PATH

COPY package.json ./
COPY package-lock.json ./

RUN npm install

COPY . .

ENV NODE_ENV=production

RUN npm run build

EXPOSE 5000
CMD ["serve", "-s", "build", "-p", "5000", "-n"]

Is it okay to have multiple Dockerfiles in a git repo with Kamal? or should I change course?

Thanks all.

[pedrosimao]

It's been longtime you posted.
But I am going through the same questions now.
From what I have researched you have two options, depending on what you want to achieve:

1 - make two distinct kamal configs which will deploy to the same server. In this case you can keep 2 distinct Dockerfile files
2 - merging the 2 Dockerfile into a single one, with multiple stages. And then adding your backend as another role then "web".

More details here:
https://kamal-deploy.org/docs/configuration/roles/

Normally only the "web" role will get the proxy by default. But this could also be changed (in case you need your secondary role to be accessible externally via a domain name).

Anyway, did you advance with your project?
I would love to know more.