Networking (11%)

Understand the networking configuration on the cluster nodes.
Understand Pod networking concepts.
Understand service networking.
Know how to use Ingress rules.
Know how to configure and use the cluster DNS.
Understand CNI.

Exercise

Check the port range that it is possible to use in your cluster.

show

# check the name of the apiserver pod
kubectl get pods -n kube-system
NAME                                      READY   STATUS             RESTARTS   AGE
coredns-fb8b8dccf-hfsxj                   1/1     Running            1          19m
coredns-fb8b8dccf-vc7jt                   1/1     Running            1          19m
etcd-master                               1/1     Running            0          18m
kube-apiserver-master                     1/1     Running            0          18m
kube-controller-manager-master            1/1     Running            0          18m
kube-keepalived-vip-hq77s                 1/1     Running            0          19m
kube-proxy-82kqs                          1/1     Running            0          19m
kube-proxy-dn5h6                          1/1     Running            0          19m
kube-scheduler-master                     1/1     Running            0          18m
weave-net-kcg9q                           2/2     Running            1          19m
weave-net-rgf92                           2/2     Running            1          19m

kubectl get pods -n kube-system -o yaml kube-apiserver-master | grep service-node-port-range
<empty output>

This means that we are using the default configuration.

Pod range: 30000-32767

Change the port range to 30000-30100 used by kubernetes to create NodePort services.

show

vim /etc/kubernetes/manifests/kube-apiserver.yaml
Add the following line in the command tag:
    - --service-node-port-range=30000-30100

# check it:
kubectl get pods -n kube-system -o yaml kube-apiserver-master | grep service-node-port-range

Create a ClusterIP service named my-cluster-headless-svc (in headless mode).
show
```
kubectl create service clusterip my-cluster-headless-svc --clusterip="None"
```
Create a ClusterIP service named my-cluster-svc with target port 8080 and port 80.
show
```
kubectl create service clusterip my-cluster-svc --tcp=80:8080
```
Create a NodePort service named my-nodeport-1-svc using with target port 8080 and port 5678. Do not specify a node-port.
show
```
kubectl create service nodeport my-nodeport-1-svc --tcp=5678:8080
```
Create a NodePort service named my-nodeport-2-svc using with target port 8080, port 5678 and node-port 20000.
show
```
kubectl create service nodeport my-nodeport-2-svc --tcp=5678:8080  --node-port=20000
```
The Service "my-nodeport-2-svc" is invalid: spec.ports[0].nodePort: Invalid value: 20000: provided port is not in the valid range. The range of valid ports is 30000-30100
Create a NodePort service named my-nodeport-2-svc using with target port 8080, port 5678 and node-port 30010.
show
```
kubectl create service nodeport my-nodeport-2-svc --tcp=5678:8080  --node-port=30010
```
Create a LoadBalancer service named my-lbs
show
```
solution
```
Create a ExternalName service named my-en-svc using with target port 8080, port 80 and external name of service google.es
show
```
 kubectl create service externalname my-en-svc --external-name=google.es --tcp=80:8080
```

Create a Cluster IP multi-Port services.

show

kubectl create service clusterip multi-port-svc --tcp=80:9376 --tcp=443:9377

Check the service-cluster-ip-range CIDR range that is configured for the API server in your cluster.

show

kubectl get pods -n kube-system -o yaml kube-apiserver-master | grep service-cluster-ip-range
    - --service-cluster-ip-range=10.96.0.0/12

For example, if you have a Service called "my-service" in a Kubernetes Namespace "my-ns", the control plane and the DNS Service acting together create a DNS record for "my-service.my-ns". Pods in the "my-ns" Namespace should be able to find it by simply doing a name lookup for my-service ("my-service.my-ns" would also work).
show
```
solution
```
Kubernetes also supports DNS SRV (Service) records for named ports. If the "my-service.my-ns" Service has a port named "http" with protocol set to TCP, you can do a DNS SRV query for _http._tcp.my-service.my-ns to discover the port number for "http", as well as the IP address.
show
```
solution
```
For example, if you start kube-proxy with the --nodeport-addresses=127.0.0.0/8 flag, kube-proxy only selects the loopback interface for NodePort Services. The default for --nodeport-addresses is an empty list. This means that kube-proxy should consider all available network interfaces for NodePort. (That’s also compatible with earlier Kubernetes releases).
show
```
solution
```
Create a pods exposing a services and check the enviroment variables.

Kubelet adds a set of environment variables for each active Service.
show
```
kubectl run --generator=run-pod/v1 nginx --image=nginx --port 80 --expose

kubectl exec nginx -- printenv | grep NGINX
```

Check your pods’ IPs, You should be able to ssh into any node in your cluster and curl both IPs.

show

kubectl get pods -o wide
NAME    READY   STATUS    RESTARTS   AGE    IP          NODE     NOMINATED NODE   READINESS GATES
nginx   1/1     Running   0          2m5s   10.44.0.1   node01   <none>           <none>

From the node01:
curl 10.44.0.1

Check the endpoints, and note that the IPs are the same as the Pods created in the first step.
show
```
kubectl describe svc nginx
kubectl get ep nginx
```
What is the network interface configured for cluster connectivity on the master node?
show
```
ip link
```
IP address assigned to the master node.
show
```
ip addr
```
Ip address assigned to the node02.
show
```
kubectl get nodes -o wide
```
What is the interface/bridge created by docker on this host
show
```
ssh node02  ; ip addr
```
State of the interface docker0
show
```
ip link show docker0
```
What is the IP address of the Default Gateway?
show
```
ip route show default
```
What is the port the kube-proxy is listing on in the master node?
show
```
netstat -nplt
```
Inspect the kubelet service and identify the network plugin configured for Kubernetes.
show
```
master $ ps aux | grep kubelet
```

root 1621 2.7 4.9 833032 101036 ? Ssl 15:08 0:20 /usr/bin/kubelet --bootstrap-kubeconfig=/etc/kubernetes/bootstrap-kubelet.conf --kubeconfig=/etc/kubernetes/kubelet.conf --config=/var/lib/kubelet/config.yaml --cgroup-driver=cgroupfs --cni-bin-dir=/opt/cni/bin --cni-conf-dir=/etc/cni/net.d --network-plugin=cni ```

</p>
</details>

What binary executable file will be run by kubelet after a container and its associated namespace are created.
show
```
cat /etc/cni/net.d/10-weave.conf
```
What is the POD IP address range configured by weave?
show
```
ip addr show weave
```

What is the default gateway configured on the PODs scheduled on node03?

show

ssh node03 ip route
10.32.0.0/12 dev weave  proto kernel  scope link  src 10.38.0.0

What network range are the nodes in the cluster part of?
show
```
ip addr
```
What is the range of IP addresses configured for PODs on this cluster?
show
```
kubectl logs -n kube-system weave-net-94n72 -c weave | grep ipalloc
```

What is the IP Range configured for the services within the cluster?

show

kubectl describe pods -n kube-system kube-apiserver-master | grep service

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