apk does not honor http_proxy env var
Error while updating a package:
/home/leo # apk add -u apk-tools
WARNING: Failed to open index for http://alpine.nethq.org/alpine/v1.9/packages/main
Use proxy to download index and packages
I think the same would apply for ftp_proxy. I haven’t tested it though.
(from redmine: issue id 137, created on 2009-08-17, closed on 2009-08-18)