feature: bootstrap daemon to boot a fresh node

[muhamadazmy]

The bootstrap daemon requirements:

• A bootstrap daemon (as the name suggests) runs only on booting a new node. It's considered an error to re-run bootstrap after the node it booted, and measures should be taken to prevent it from re-running otherwise it can interfere with the node runtime.
• The bootstrap daemon should have NO dependency on node daemons (0-OS daemons) but of course is allowed to use the embedded tools in the image.
• bootstrap needs to make sure node can reach the internet (or nearby hub) to download flist of latest binaries).
• a tmpfs is created and used as a cache backend for the boot flist
• after mounting the flist ALL files are copied to the rootfs of the node
• all new yaml files under /etc/zinit/ are monitored
• bootstrap unmount the boot flist, and remove the tmpfs mount

[muhamadazmy]

The first issue we need to discuss is networking. 0-initramfs used to have a simple unit file that boots dhcpcd on the available network card(s). But it was removed in fever of networkd.

I think we can bring this back (with some improvements) and we make it responsibility of networkd to stop this service before taking over the machine networking stack.

Later on, bootstrap can only then depend on this internet service, and we grantee a smooth boot and running of the service

[zaibon]

I think we can bring this back (with some improvements) and we make it responsibility of networkd to stop this service before taking over the machine networking stack.

I don't have a problem with this. Seems logical enough. @delandtj ?

[delandtj]

for networking https://github.com/threefoldtech/zosv2/pull/236 addresses the bootstrap part of the network, as I think some simple dhcp runs on interfaces will not cope with some more complex setups. It will never be as simple, and now in bootstrap we can set a krnl cmdline to include or exclude interfaces, as that will come up in the future. also commented in the meeting notes 20190909