--flannel-backend=none doesn't work on agent, but --no-flannel works

[j4m3s-s]

Environmental Info:
K3s Version: 1.21.0+k3s1

Node(s) CPU architecture, OS, and Version:

x86_64, NixOS 21.11
Cluster Configuration:

3 servers, 83 agents
Describe the bug:

--flannel-backend=none doesn't work. --no-flannel is deprecated but works.
Steps To Reproduce:

/nix/store/f1f0my79gzkibfcmvlcf3hvvicd08vzx-k3s-1.21.0+k3s1/bin/k3s agent   --docker      --server https://10.224.33.248:6443   --token-file /var/lib/rancher/k3s_token   --flannel-backend=none   --pause-image registry.gitlab.com/risson/prologin-sadm-2021/rancher/pause:3.1
Incorrect Usage: flag provided but not defined: -flannel-backend

NAME:
   k3s agent - Run node agent

USAGE:
   k3s agent [OPTIONS]

OPTIONS:
   --config FILE, -c FILE              (config) Load configuration from FILE (default: "/etc/rancher/k3s/config.yaml") [$K3S_CONFIG_FILE]
   --debug                             (logging) Turn on debug logs [$K3S_DEBUG]
   -v value                            (logging) Number for the log level verbosity (default: 0)
   --vmodule value                     (logging) Comma-separated list of pattern=N settings for file-filtered logging
   --log value, -l value               (logging) Log to file
   --alsologtostderr                   (logging) Log to standard error as well as file (if set)
   --token value, -t value             (cluster) Token to use for authentication [$K3S_TOKEN]
   --token-file value                  (cluster) Token file to use for authentication [$K3S_TOKEN_FILE]
   --server value, -s value            (cluster) Server to connect to [$K3S_URL]
   --data-dir value, -d value          (agent/data) Folder to hold state (default: "/var/lib/rancher/k3s")
   --node-name value                   (agent/node) Node name [$K3S_NODE_NAME]
   --with-node-id                      (agent/node) Append id to node name
   --node-label value                  (agent/node) Registering and starting kubelet with set of labels
   --node-taint value                  (agent/node) Registering kubelet with set of taints
   --docker                            (agent/runtime) Use docker instead of containerd
   --container-runtime-endpoint value  (agent/runtime) Disable embedded containerd and use alternative CRI implementation
   --pause-image value                 (agent/runtime) Customized pause image for containerd or docker sandbox (default: "docker.io/rancher/pause:3.1")
   --snapshotter value                 (agent/runtime) Override default containerd snapshotter (default: "overlayfs")
   --private-registry value            (agent/runtime) Private registry configuration file (default: "/etc/rancher/k3s/registries.yaml")
   --node-ip value, -i value           (agent/networking) IPv4/IPv6 addresses to advertise for node
   --node-external-ip value            (agent/networking) IPv4/IPv6 external IP addresses to advertise for node
   --resolv-conf value                 (agent/networking) Kubelet resolv.conf file [$K3S_RESOLV_CONF]
   --flannel-iface value               (agent/networking) Override default flannel interface
   --flannel-conf value                (agent/networking) Override default flannel config file
   --kubelet-arg value                 (agent/flags) Customized flag for kubelet process
   --kube-proxy-arg value              (agent/flags) Customized flag for kube-proxy process
   --protect-kernel-defaults           (agent/node) Kernel tuning behavior. If set, error if kernel tunables are different than kubelet defaults.
   --rootless                          (experimental) Run rootless
   --selinux                           (agent/node) Enable SELinux in containerd [$K3S_SELINUX]
   --lb-server-port value              (agent/node) Local port for supervisor client load-balancer. If the supervisor and apiserver are not colocated an additional port 1 less than this port will also be used for the apiserver client load-balancer. (default: 6444) [$K3S_LB_SERVER_PORT]
   --no-flannel                        (deprecated) use --flannel-backend=none
   --cluster-secret value              (deprecated) use --token [$K3S_CLUSTER_SECRET]
   
FATA[0000] flag provided but not defined: -flannel-backend 

• Installed k3s : We use NixOS version packaged.
  Expected behavior:

Actual behavior:

The non-deprecated flag doesn't work, but the deprecated one does.

cc @rissson @lportemo (my fellow colleagues)

[brandond]

Like other cluster-wide configuration variables (cluster-cidr, pod-cidr, etc) the flannel configuration is set server-side and propagated to agents. If you set --flannel-backend=none on your servers, you don't need to do anything on the agent - including using deprecated flags.

Ref:
controlConfig is the configuration retrieved from the server during agent bootstrapping.

k3s/pkg/agent/config/config.go

Line 420 in 136dddc

FlannelBackend: controlConfig.FlannelBackend,

k3s/pkg/agent/config/config.go

Lines 495 to 496 in 136dddc

	if nodeConfig.FlannelBackend == config.FlannelBackendNone {
	nodeConfig.NoFlannel = true

[rissson]

Understood. Shouldn't this flag be removed from the agents altogether then?

[brandond]

It's deprecated (and documented as such) but not removed so that folks that started using it before we refactored the logic don't see agents crash due to invalid CLI flags when they upgrade.

[rissson]

Great. I think we can close this then.