Support for pre-defined user images in the iso

[niusmallnan]

Somebody wants to pre-defined images in the iso, which can address offline scenario.

Now we have supported APPEND_SYSTEM_IMAGES, it can save images to /usr/share/ros/images-system.tar, and loaded with system-docker when booting. There are a lot of demos in Makefile of rancher/os.

I will add another option APPEND_USER_IMAGES, it can save images to /usr/share/ros/images-user.tar. ROS will not load this image, you can deal with it by yourself. ROS can load this image with user-docker.
You can build ISO like this:

APPEND_USER_IMAGES="alpine ubuntu" make

Please note that these will be packaged into the initrd, and the predefined images will take up the resource footprint at startup.

[crochik]

@niusmallnan I do appreciate it! Just out of curiosity: is there any reason why we wouldn't want to make part of the "install" process to copy those to the preload folder?

[niusmallnan]

@crochik I see that you want an offline ISO with pre-defined images.
I think that it should be hard for you to get an ISO file, if adding pre-defined images to "install" process.

[rootwuj]

Tested with rancher/os:v1.5.2-rc1 from May 24

Step:

• Use APPEND_USER_IMAGES="alpine ubuntu nginx" make build ISO.
• Use this ISO to deploy offline environment.
• Validate /usr/share/ros/images-user.tar exist.
• Use docker images to validate that the pre-defined image has been loaded.
• Delete all user-docker images and validate that they can reload after reboot

Verified fixed.