Allow flannel interface to be specified on the command line

[yoink00]

This should fix #200 and #72.

I am having issues building this on my local system to test properly as dapper keeps flaking out. I am hoping someone can review this while I try and fix dapper.

[yoink00]

I've now completed testing this. My dapper problems were caused by an out-dated version of Docker.

Test setup

2 Ubuntu VMs with a GRE tunnel configured.

Test 1

Run k3s as per the quick start instructions on k3s.io:

        sudo k3s server &
        # Kubeconfig is written to /etc/rancher/k3s/k3s.yaml
        sudo k3s kubectl get node

        # On a different node run the below. NODE_TOKEN comes from /var/lib/rancher/k3s/server/node-token
        # on your server
        sudo k3s agent --server https://192.168.1.24:6443 --token ${NODE_TOKEN}

Check agent log file to ensure that default interface is selected for flannel. Run a simple load and monitor network traffic using iftop.

Test 2

Run k3s specifying tunnel IP and flannel interface:

        sudo k3s server --node-ip 10.10.10.1 --flannel-iface gre1 &
        # Kubeconfig is written to /etc/rancher/k3s/k3s.yaml
        sudo k3s kubectl get node

        # On a different node run the below. NODE_TOKEN comes from /var/lib/rancher/k3s/server/node-token
        # on your server
        sudo k3s agent --server https://10.10.10.1:6443 --flannel-iface gre1 --node-ip 10.10.10.2 --token ${NODE_TOKEN}

Check agent log file to ensure that gre1 interface is selected for flannel. Run a simple load and monitor network traffic using iftop.

Result

Both tests behaved as I expected.

[yoink00]

Resolved conflicts

[deniseschannon]

@galal-hussein can you review this?

[galal-hussein]

LGTM, @yoink00 can you squash your commits

[yoink00]

@galal-hussein Commits squashed. Thanks!