Self-host Kamal

copy# Kamal — deploys a containerised web app to servers over SSH, run from your workstation (gem install kamal is the official install). Pinned to 2.12.0. Prerequisites: SSH access to the server as a user in the docker group, and Docker on the server. Replace SERVER_IP and SSH_USER; here the workstation and the server are the same machine.
sudo apt-get update && sudo apt-get install -y ruby-full build-essential git
sudo gem install kamal -v 2.12.0 --no-document
# images go through a registry the server can pull from. With a separate server, `server: localhost:5555` makes Kamal run a temporary registry and tunnel it over SSH; that port collides when workstation and server are one machine, so this run starts its own.
docker run -d --restart unless-stopped --name registry -p 127.0.0.1:5000:5000 registry:3.1.2
mkdir demo && cd demo && git init -q
# a minimal app: Kamal's proxy waits for GET /up to return 200 before it routes traffic
cat > Dockerfile << 'EOF'
FROM nginx:1.30-alpine
RUN echo ok > /usr/share/nginx/html/up
EOF
kamal init
cat > config/deploy.yml << 'EOF'
service: demo
image: demo
servers:
  web:
    - SERVER_IP
ssh:
  user: SSH_USER
proxy:
  app_port: 80
  healthcheck:
    path: /up
registry:
  server: 127.0.0.1:5000
  username: demo
  password:
    - KAMAL_REGISTRY_PASSWORD
builder:
  arch: amd64
  driver: docker
EOF
# Kamal tags each release with the git commit
git add -A && git -c user.name=demo -c user.email=demo@example.com commit -qm demo
# Kamal insists on registry credentials even though this local registry does not check them
echo 'KAMAL_REGISTRY_PASSWORD=$KAMAL_REGISTRY_PASSWORD' >> .kamal/secrets
export KAMAL_REGISTRY_PASSWORD=unused
kamal setup
# the app answers at http://SERVER_IP on port 80