MetalLB: fail if kube_proxy_strict_arp is false (#5180)

When using IPVS, kube_proxy_strict_arp = true is required
https://github.com/danderson/metallb/issues/153#issuecomment-518651132

Add kube_proxy_strict_arp to inventory/sample

contrib/metallb/roles/provision/tasks/main.yml

 ---
+- name: "Kubernetes Apps | Check cluster settings for MetalLB"
+  fail:
+    msg: "MetalLB require kube_proxy_strict_arp = true, see https://github.com/danderson/metallb/issues/153#issuecomment-518651132"
+  when:
+    - "kube_proxy_mode == 'ipvs' and not kube_proxy_strict_arp"
 - name: "Kubernetes Apps | Lay Down MetalLB"
   become: true
   template: { src: "{{ item }}.j2", dest: "{{ kube_config_dir }}/{{ item }}" }

inventory/sample/group_vars/k8s-cluster/k8s-cluster.yml

@@ -101,6 +101,10 @@ kube_apiserver_insecure_port: 0  # (disabled)
 # Can be ipvs, iptables
 kube_proxy_mode: ipvs
 
+# configure arp_ignore and arp_announce to avoid answering ARP queries from kube-ipvs0 interface
+# must be set to true for MetalLB to work
+kube_proxy_strict_arp: false
+
 # A string slice of values which specify the addresses to use for NodePorts.
 # Values may be valid IP blocks (e.g. 1.2.3.0/24, 1.2.3.4/32).
 # The default empty string slice ([]) means to use all local addresses.

roles/kubernetes/master/defaults/main/kube-proxy.yml

@@ -80,6 +80,8 @@ kube_proxy_exclude_cidrs: []
 # nq: never queue
 kube_proxy_scheduler: rr
 
+# configure arp_ignore and arp_announce to avoid answering ARP queries from kube-ipvs0 interface
+# must be set to true for MetalLB to work
 kube_proxy_strict_arp: false
 
 # The IP address and port for the metrics server to serve on