Minimal Firewall Exceptions

[dereknola]

Changes

• While it is recommended disable firewalls, you can get minimum viable K3s working with a few exceptions. This adds support for ufw and firewalld, the two most common firewalls.
• Modifying k3s configuration from default such as --service-cidr would invalidate these exceptions. This is barebones, its left to the user to modify the firewall if they want more exceptions. See https://docs.k3s.io/installation/requirements#inbound-rules-for-k3s-server-nodes from the most common ports/rules.

Testing

Tested on HA configurations of:

• ubuntu 20.04 with UFW enabled
• rocky 8 with firewalld enabled

Linked Issues

#234