[SOLVED] --publish-all not publishing EXPOSEd port

--publish-all not publishing EXPOSEd port

Here is a basic Docker NGINX image:

FROM nginx:alpine
COPY src /usr/share/nginx/html
EXPOSE 80

The image's metadata includes the exposed port:

> docker inspect --format '{{json .Config.ExposedPorts}}' ...
{"80/tcp":{}}

But when running it with docker run --publish-all the server is not accessible.
It must be run with docker run --publish 80:80.

But isn't the point of EXPOSE to document the image's port so they can be published without having to be explicitly listed thanks to --publish-all?

Solution

The --publish-all flag publishes the "exposed ports to ephemeral ports".

So, you'll get something like:

docker container inspect nginx --format=json \
| jq -r '.[0].NetworkSettings.Ports'

{
  "80/tcp": [
    {
      "HostIp": "0.0.0.0",
      "HostPort": "32769"
    }
  ]
}

Where, in this case, the container port 80 is mapped to the host's 32769 (not 80).