fixing "Could not handshake: An unexpected TLS packet was received" error while apt update in docker container behind corporate proxy

Background

While trying to build a docker image from a very raw apache spark base image, since it didn’t have any basic packages such as vim, ssh, wget, etc, I entered a running container of this image and typed apt update but the following error msg was returned

Could not handshake: An unexpected TLS packet was received

This error message did not go away even though I set the http_proxy and https_proxy environment variable.

BTW, I was trying to build this docker image on a server which was behind a corporate proxy. Also when creating the container, I allowed host network access so that it can access “localhost:7007” which is a port that points to the corporate proxy.

Solution

The solution that worked for me was from this stackoverflow answer.

I manually created a file /etc/apt/apt.conf.d/05proxy and added the following lines

Acquire::http::proxy "http://localhost:7007";
Acquire::https::proxy "http://localhost:7007";

where “localhost:7007” is where I have opened a port to be directed to my corporate proxy. Note that even for https proxy, I have forced it to point to http of proxy.

After adding this file and running apt update works.