Dockerfile ADD: x509: certificate signed by unknown authority

Background: I have a dockerfile that adds a file directly from an (internal) server using a URL. I am currently converting the server to use https instead of http. docker is giving me the message:

ADD failed: Get https://…: x509: certificate signed by unknown authority

This is not totally surprising. It is an internal server and in other cases I’ve have to add the public keys into the trusted cert area. I’ve done this for the host environment and it now works for (e.g.). I assume since the above fails, then there is a separate way of adding to the docker engine.

Question: are there any instructions for this?

Virtually all the links I see regarding certificates are to do with signed registry access.

OK I can answer this myself. I rebooted the host machine and it seems to be fine. I initially tried to reboot just docker and that failed, but might have been for another reason.