Docker + Nginx + Let's Encrypt

This post shows how to set up multiple websites running behind a dockerized Nginx reverse proxy and served via HTTPS using free Let’s Encrypt certificates. New sites can be added on the fly by just modifying docker-compose.yml and then running docker-compose up as the main Nginx config is automatically updated and certificates (if needed) are automatically acquired.

Some of the configuration is derived from https://github.com/fatk/docker-letsencrypt-nginx-proxy-companion-examples with some simplifications and updates to work with current nginx.tmpl from nginx-proxy and docker-compose v2 files.

Running the example

The repository for this is at https://github.com/gilyes/docker-nginx-letsencrypt-sample.

Prerequisites

docker (>= 1.10)
docker-compose (>= 1.8.1)
access to (sub)domain(s) pointing to a publicly accessible server (required for TLS)

Preparation

Clone the repository on the server pointed to by your domain.
In docker-compose.yml:
- Change the VIRTUAL_HOST and LETSENCRYPT_HOST entries from sampleapi.example.com and samplewebsite.example.com to your domains.
- Change LETSENCRYPT_EMAIL entries to the email address you want to be associated with the certificates.
In volumes/config/sample-website/config.js change apiUrl to your API endpoint as set up in the previous point in docker-compose.yml.

Running

In the main directory run:

docker-compose up

This will perform the following steps:

Download the required images from Docker Hub (nginx, docker-gen, docker-letsencrypt-nginx-proxy-companion).
Create containers from them.
Build and create containers for the two sites located in sample-websites.
Start up the containers.
- docker-letsencrypt-nginx-proxy-companion inspects containers’ metadata and tries to acquire certificates as needed (if successful then saving them in a volume shared with the host and the Nginx container).
- docker-gen also inspects containers’ metadata and generates the configuration file for the main Nginx reverse proxy

If everything went well then you should now be able to access your website at the provided address.

Troubleshooting

To view logs run docker-compose logs.
To view the generated Nginx configuration run docker exec -ti nginx cat /etc/nginx/conf.d/default.conf

How does it work

The system consists of 4 main parts:

Main Nginx reverse proxy container.
Container that generates the main Nginx config based on container metadata.
Container that automatically handles the acquisition and renewal of Let’s Encrypt TLS certificates.
The actual websites living in their own containers. In this example, a very simple website, talking to a very simple API.

The main Nginx reverse proxy container

This is the only publicly exposed container, routes traffic to the backend servers and provides TLS termination.

Uses the official nginx Docker image.

It is defined in docker-compose.yml under the nginx service block:

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services:
  nginx:
    restart: always
    image: nginx
    container_name: nginx
    ports:
      - "80:80"
      - "443:443"
    volumes:
      - "/etc/nginx/conf.d"
      - "/etc/nginx/vhost.d"
      - "/usr/share/nginx/html"
      - "./volumes/proxy/certs:/etc/nginx/certs:ro"

As you can see it shares a few volumes:

Configuration folder: used by the container that generates the configuration file.
Default Nginx root folder: used by the Let’s Encrypt container for challenges from the CA.
Certificates folder: written to by the Let’s Encrypt container, this is where the TLS certificates are maintained.

The configuration generator container

This container inspects the other running containers and based on their metadata (like VIRTUAL_HOST environment variable) and a template file it generates the Nginx configuration file for the main Nginx container. When a new container is spinning up this container detects that, generates the appropriate configuration entries and restarts Nginx.

Uses the jwilder/docker-gen Docker image.

It is defined in docker-compose.yml under the nginx-gen service block:

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services:
  ...

  nginx-gen:
    restart: always
    image: jwilder/docker-gen
    container_name: nginx-gen
    volumes:
      - "/var/run/docker.sock:/tmp/docker.sock:ro"
      - "./volumes/proxy/templates/nginx.tmpl:/etc/docker-gen/templates/nginx.tmpl:ro"
    volumes_from:
      - nginx
    entrypoint: /usr/local/bin/docker-gen -notify-sighup nginx -watch -wait 5s:30s /etc/docker-gen/templates/nginx.tmpl /etc/nginx/conf.d/default.conf

The container reads the nginx.tmpl template file (source: jwilder/nginx-proxy) via a volume shared with the host.

It also mounts the Docker socket into the container in order to be able to inspect the other containers (the "/var/run/docker.sock:/tmp/docker.sock:ro" line). Security warning: mounting the Docker socket is usually discouraged because the container getting (even read-only) access to it can get root access to the host. In our case, this container is not exposed to the world so if you trust the code running inside it the risks are probably fairly low. But definitely something to take into account. See e.g. The Dangers of Docker.sock for further details.

NOTE: it would be preferrable to have docker-gen only handle containers with exposed ports (via -only-exposed flag in the entrypoint script above) but currently that does not work, see e.g. https://github.com/jwilder/nginx-proxy/issues/438.

The Let’s Encrypt container

This container also inspects the other containers and acquires Let’s Encrypt TLS certificates based on the LETSENCRYPT_HOST and LETSENCRYPT_EMAIL environment variables. At regular intervals it checks and renews certificates as needed.

Uses the jrcs/letsencrypt-nginx-proxy-companion Docker image.

It is defined in docker-compose.yml under the letsencrypt-nginx-proxy-companion service block:

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services:
  ...

  letsencrypt-nginx-proxy-companion:
    restart: always
    image: jrcs/letsencrypt-nginx-proxy-companion
    container_name: letsencrypt-nginx-proxy-companion
    volumes_from:
      - nginx
    volumes:
      - "/var/run/docker.sock:/var/run/docker.sock:ro"
      - "./volumes/proxy/certs:/etc/nginx/certs:rw"
    environment:
      - NGINX_DOCKER_GEN_CONTAINER=nginx-gen

The container uses a volume shared with the host and the Nginx container to maintain the certificates.

It also mounts the Docker socket in order to inspect the other containers. See the security warning above in the docker-gen section about the risks of that.

The sample website and the sample API

These two very simple samples are running in their own respective containers. They are defined in docker-compose.yml under the sample-api and sample-website service blocks:

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services:
  ...

  sample-api:
    restart: always
    image: sample-api
    build: ./samples/api
    container_name: sample-api
    environment:
      - VIRTUAL_HOST=sampleapi.example.com
      - VIRTUAL_NETWORK=nginx-proxy
      - VIRTUAL_PORT=3000
      - LETSENCRYPT_HOST=sampleapi.example.com
      - [email protected]

  sample-website:
    restart: always
    image: sample-website
    build: ./samples/website
    container_name: sample-website
    volumes:
      - "./volumes/nginx-sample-website/conf.d/:/etc/nginx/conf.d"
      - "./volumes/config/sample-website/config.js:/usr/share/nginx/html/config.js"
    environment:
      - VIRTUAL_HOST=samplewebsite.example.com
      - VIRTUAL_NETWORK=nginx-proxy
      - VIRTUAL_PORT=80
      - LETSENCRYPT_HOST=sample.example.com
      - [email protected]

The important part here are the environment variables. These are used by the config generator and certificate maintainer containers to set up the system.

The source code for these two images is in the samples subfolder, the images are built from there. In a real-world scenario these images would likely come from a Docker registry.

Conclusion

This can be a fairly simple way to have easy, reproducible deploys for websites with free, auto-renewing TLS certificates.