Merge pull request #367 from louiznk/docs/replace-flannel-with-calico

docs: add guide on using calico instead of flannel (thanks @louiznk)

docs/usage/guides/.pages

@@ -2,3 +2,4 @@ title: Guides
 arrange:
   - exposing_services.md
   - registries.md
+  - calico.md

docs/usage/guides/calico.md

@@ -0,0 +1,67 @@
+# Use Calico instead of Flannel
+If you want to use NetworkPolicy you can use Calico in k3s instead of Flannel.
+
+### 1. Download and modify the Calico descriptor
+You can following the [documentation](https://docs.projectcalico.org/master/reference/cni-plugin/configuration)
+
+And then you have to change the ConfigMap `calico-config`. On the `cni_network_config` add the entry for allowing IP forwarding  
+```json
+    "container_settings": {
+        "allow_ip_forwarding": true
+    }
+```
+Or you can directly use this [calico.yaml](calico.yaml) manifest
+
+## 2. Create the cluster without flannel and with calico
+On the k3s cluster creation :
+- add the flag `--flannel-backend=none`. For this, on k3d you need to forward this flag to k3s with the option `--k3s-server-arg`.
+- mount (`--volume`) the calico descriptor in the auto deploy manifest directory of k3s `/var/lib/rancher/k3s/server/manifests/`
+
+So the command of the cluster creation is (when you are at root of the k3d repository)
+```bash
+    k3d cluster create "${clustername}" --k3s-server-arg '--flannel-backend=none' --volume "$(pwd)/docs/usage/guides/calico.yaml:/var/lib/rancher/k3s/server/manifests/calico.yaml"
+```
+In this example :
+- change `"${clustername}"` with the name of the cluster (or set a variable). 
+- `$(pwd)/docs/usage/guides/calico.yaml` is the absolute path of the calico manifest, you can adapt it.
+
+You can add other options, [see](../commands.md).  
+
+The cluster will start without flannel and with Calico as CNI Plugin.
+
+For watching for the pod(s) deployment
+```bash
+    watch "kubectl get pods -n kube-system"    
+```
+
+You will have something like this at begining (with the command line `kubectl get pods -n kube-system`)
+```
+NAME                                       READY   STATUS     RESTARTS   AGE
+helm-install-traefik-pn84f                 0/1     Pending    0          3s
+calico-node-97rx8                          0/1     Init:0/3   0          3s
+metrics-server-7566d596c8-hwnqq            0/1     Pending    0          2s
+calico-kube-controllers-58b656d69f-2z7cn   0/1     Pending    0          2s
+local-path-provisioner-6d59f47c7-rmswg     0/1     Pending    0          2s
+coredns-8655855d6-cxtnr                    0/1     Pending    0          2s
+```
+
+And when it finish to start
+```
+NAME                                       READY   STATUS      RESTARTS   AGE
+metrics-server-7566d596c8-hwnqq            1/1     Running     0          56s
+calico-node-97rx8                          1/1     Running     0          57s
+helm-install-traefik-pn84f                 0/1     Completed   1          57s
+svclb-traefik-lmjr5                        2/2     Running     0          28s
+calico-kube-controllers-58b656d69f-2z7cn   1/1     Running     0          56s
+local-path-provisioner-6d59f47c7-rmswg     1/1     Running     0          56s
+traefik-758cd5fc85-x8p57                   1/1     Running     0          28s
+coredns-8655855d6-cxtnr                    1/1     Running     0          56s
+```
+
+Note : 
+- you can use the auto deploy manifest or a kubectl apply depending on your needs
+- <!> Calico is not as quick as Flannel (but it provides more features)
+
+## References
+https://rancher.com/docs/k3s/latest/en/installation/network-options/  
+https://docs.projectcalico.org/getting-started/kubernetes/k3s/