TLS Timeout when using docker run/pull on Raspberry Pi Zero W

[donkawechico]

ISSUE:

On a Raspberry Pi Zero W, when pulling/downloading the latest magic-cards image layers via the docker run step in the README, it eventually fails with the error:

error pulling image configuration: Get https://production.butt //...// : net/http: TLS handshake timeout

CAUSE

Docker, by default, runs 3 simultaneous network connections when pulling down docker image layers, which overwhelms the Zero W.

SOLUTION:

Set the max-concurrent-downloads parameter, as described here: https://forums.docker.com/t/tls-handshake-timeout-pulling-from-docker-hub-on-a-raspberry-pi-1-on-docker-17-03/53614/2

It can also be done when starting the docker daemon by stopping the daemon, then starting manually with:
dockerd --max-concurrent-downloads 1

Once the docker pull is complete, you can relaunch the daemon with the default of 3 connections.

Might be worth adding an entry in the README to reflect this, as I suspect it would occur for all/most pi zeros.