This Docker image is based on the awesome smallstep/cli and smallstep/certificates projects from smallstep.

Getting started

$ docker run --name ca.internal --restart unless-stopped -v step:/home/step -d katoni/simple-acme-server

Download Root CA from container:

$ docker cp ca.internal:/home/step/certs/root_ca.crt .

Install the Root CA into your Trusted Root Certification Authorities store.

Containers in the same network can access the ACME server with this URL: https://ca.internal/acme/development/directory

Access from another container

Example with Traefik reverse proxy:

services:
  traefik:
    image: traefik
    command:
      - "--log.level=DEBUG"
      - "--providers.docker=true"
      - "--entrypoints.http.address=:80"
      - "--certificatesResolvers.internal.acme.email=your-email@your-domain.org"
      - "--certificatesResolvers.internal.acme.httpChallenge=true"
      - "--certificatesResolvers.internal.acme.httpChallenge.entryPoint=http"
      - "--certificatesResolvers.internal.acme.caServer=https://ca.internal/acme/development/directory"
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
      - ./ca.pem:/ca.pem
    environment:
      LEGO_CA_CERTIFICATES: /ca.pem

Note: Docker Desktop (since version 1.12.1) recognizes certs stored under Trust Root Certification Authorities or Intermediate Certification Authorities. However, there appears to be an issue (docker/for-win#4804), so we have to manually mount the root CA. Use LEGO_CA_CERTIFICATES to configure the lego client to use our custom CA certificate.

Credits

https://smallstep.com/blog/private-acme-server/