We have a small fleet of DS-5/Development Studio projects that target Cyclone V and we're interested in building these projects in containers. Some questions:
That does sound like it would do the trick, but due to the resulting image size/speed we ended up starting with an Ubuntu image and installing ARMDS and a specific version of the ARM compiler requested by the developers and that seems to be working well.
Unfortunately, they appear to have been using a customized version of mkimage in the post-build step that was only built as a Windows exe years ago. I had installed the latest u-boot-tools apt package, but that was apparently generating an img file that had a checksum that didn't match prior builds of the same source.
I was surprised (being new to ES) to find this article: https://www.rocketboards.org/foswiki/Documentation/BuildingBootloaderCycloneVAndArria10 where the instructions have you build u-boot from source.