I have been doing Ubuntu deployment using a preseed.cfg. After becoming comfortable with the packages being installed it was time to reduce download time and internet traffic by creating a mirror. I ended up doing a "partial mirror" using apt-cacher-ng and preseeding it by adding
d-i mirror/http/proxy string http://mymirror
to the preseed.cfg. This is where things got strange. I have a few .debs that I run as part of preseed/late_command by wgetting them and installing them with dpkg -i. The packages were installing without issue until added the proxy. With the proxy they fail to install. So does the proxy affect installing .debs during preseeded installation?