docker-letsencrypt-nginx-proxy-companion/docs/Getting-containers-IDs.md

Getting nginx-proxy/nginx/docker-gen containers IDs

For acme-companion to work properly, it needs to know the ID of the nginx/nginx-proxy container (in both two and three containers setups), plus the ID of the docker-gen container in a three container setup.

There are three methods to inform the acme-companion container of the nginx/nginx-proxy container ID:

• label method: add the label com.github.nginx-proxy.nginx to the nginx/nginx-proxy container.

• environment variable method: assign a fixed name to the nginx/nginx-proxy container with container_name: and set the environment variable NGINX_PROXY_CONTAINER to this name on the acme-companion container.

• volumes_from method. Using this method, the acme-companion container will get the nginx/nginx-proxy container ID from the volumes it got using the volumes_from option.

And two methods to inform the acme-companion container of the docker-gen container ID:

• label method: add the label com.github.nginx-proxy.docker-gen to the docker-gen container.

• environment variable method: assign a fixed name to the docker-gen container with container_name: and set the environment variable NGINX_DOCKER_GEN_CONTAINER to this name on the acme-companion container.

The methods for each container are sorted by order of precedence, meaning that if you use both the label and the volumes_from method, the ID of the nginx/nginx-proxy container that will be used will be the one found using the label. There is no point in using more than one method at a time for either the nginx/nginx-proxy or docker-gen container beside potentially confusing yourself.

The advantage the label methods have over the environment variable (and volumes_from) methods is enabling the use of the acme-companion in environments where containers names are dynamic, like in Swarm Mode or in Docker Cloud. Howhever if you intend to do so, as upstream docker-gen lacks the ability to identify containers from labels, you'll need both to either use the two containers setup or to replace nginx-proxy/docker-gen with a fork that has this ability like herlderco/docker-gen. Be advised that for now, this works to a very limited extent (everything has to be on the same node).

Examples with three containers setups:

label method.

$ docker run --detach \
    [...]
    --label com.github.nginx-proxy.nginx \
    nginx

$ docker run --detach \
    [...]
    --label com.github.nginx-proxy.docker-gen \
    nginxproxy/docker-gen

$ docker run --detach \
    [...]
    nginxproxy/acme-companion

environment variable method

$ docker run --detach \
    [...]
    --name unique-container-name \
    nginx

$ docker run --detach \
    [...]
    --name another-unique-container-name \
    nginxproxy/docker-gen

$ docker run --detach \
    [...]
    --env NGINX_PROXY_CONTAINER=unique-container-name \
    --env NGINX_DOCKER_GEN_CONTAINER=another-unique-container-name \
    nginxproxy/acme-companion

volumes_from (nginx) + label (docker-gen) method

$ docker run --detach \
    [...]
    --name unique-container-name \
    nginx

$ docker run --detach \
    [...]
    --label com.github.nginx-proxy.docker-gen \
    nginxproxy/docker-gen

$ docker run --detach \
    [...]
    --volumes-from unique-container-name \
    nginxproxy/acme-companion

volumes_from (nginx) + environment variable (docker-gen) method

$ docker run --detach \
    [...]
    --name unique-container-name \
    nginx

$ docker run --detach \
    [...]
    --name another-unique-container-name \
    nginxproxy/docker-gen

$ docker run --detach \
    [...]
    --volumes-from unique-container-name \
    --env NGINX_DOCKER_GEN_CONTAINER=another-unique-container-name \
    nginxproxy/acme-companion