Container Linux migration documentation

[bgilbert]

Spun out from #48.

The Container Linux distro currently has a planned EOL in 2020, and users will need to migrate to Fedora CoreOS to remain supported. We'll need to document the differences to make the migration as painless as possible.

This bug tracks known differences that need to be documented.

Installation

• coreos-install -> coreos-installer
• Autologin kernel command-line parameter (Consider adding kernel command-line argument for automatically logging in on console #112)
• Migrating from CL image types to FCOS ones
• Vagrant images (Vagrant Cloud images for Fedora CoreOS #144)

User configuration

• Ignition config spec changes
• Availability of users/groups in Ignition configs (Handling of default users/groups #155)
• CLC -> FCC changes
• coreos-metadata rename: systemd services and provider variable, metadata path and variables
• PXE custom OEMs
• /etc path differences
• ntpd/systemd-timesyncd -> chronyd
• etcd
• flannel
• locksmith (reboot coordination: locksmith successor #3)
• networkd (Network Management #24)
• Password login (Consider disabling SSH password login by default #138)
• Docker version selection
• Docker configuration differences (docker group or not #2, etc.)
• Immutable root directory (Allow creation of immutable directories below root folder #270)

Operator notes

• Release streams and recommendations for production
• update-ssh-keys (Decide how to handle user SSH keys #139)
• Update system and commands
• SELinux policy differences
• toolbox differences (coreos/toolbox v2 #38)
• Custom kernel modules (Kernel Module Support #15)
• ostree, /etc, and /var
• Metrics (Collect metrics from Fedora CoreOS machines #86)
• Automatic rollback mechanism differences
• Cloud CLI clients (Cloud CLI Clients #75)
• Different behavior when opening an existing file in a sticky directory (EACCES when root opens user files with O_WRONLY|O_CREAT|O_APPEND bugs#2577)
• SMT disablement (Policy for disabling SMT #181)

Implementation notes

• Partition layout differences
• sshd socket activation
• Default filesystems (Default filesystem choices for FCOS #33)
• OEM partition support
• Automatic filesystem resizing differences (Determine how we extend partitions on boot #45)

[dhawal55]

Is torcx still going to be the tool of choice for boot-time configuration? Should we add torcx to the above list?

[bgilbert]

@dhawal55 Nope, it's not.

[bgilbert]

At this point I think it's unlikely that further work will be done here, so I propose closing this out.

[bgilbert]

Closing per #159 (comment).