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Practice Test - Explore Env

Solution

  1. How many nodes are part of this cluster? 
    kubectl get nodes

    Count the results

  2. What is the Internal IP address of the controlplane node in this cluster? 
    kubectl get nodes -o wide

    Note the value in INTERNAL-IP column for controlplane

  3. What is the network interface configured for cluster connectivity on the controlplane node?

    This will be the network interface that has the same IP address you determined in the previous question.

    ip a

    There is quite a lot of output for the above command. We can filter it better:

    ip a | grep -B2 X.X.X.X

    where X.X.X.X is the IP address you got from the previous question. grep -B2 will find the line containing the value we are looking for and print that and the previous 2 line of output. It will look like this, though the values will be different each time you run the lab.

    3058: eth0@if3059: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UP group default
   link/ether 02:42:c0:08:ea:03 brd ff:ff:ff:ff:ff:ff link-netnsid 0
  inet 192.8.234.3/24 brd 192.8.234.255 scope global eth0

    From this, we can determine the answer to be

    eth0

  4. What is the MAC address of the interface on the controlplane node?

    This value is also present in the output of the command you ran for the previous question. The MAC address is the value in the link/ether field of the output and is 6 hex numbers separated by :. Note that the value can be different each time you run the lab.

    If the output for eth0 is

    3058: eth0@if3059: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UP group default
   link/ether 02:42:c0:08:ea:03 brd ff:ff:ff:ff:ff:ff link-netnsid 0
  inet 192.8.234.3/24 brd 192.8.234.255 scope global eth0

    then the MAC address is

    02:42:c0:08:ea:03

  5. What is the IP address assigned to node01? 
    kubectl get nodes -o wide

    Note the value in INTERNAL-IP column for node01

  6. What is the MAC address assigned to node01?

    For this we will need to SSH onto node01 so we can view its interfaces. We know what IP to look for, as we determined this in the previous question

    ssh node01
ip a | grep -B2 X.X.X.X

    where X.X.X.X is the IP address you got from the previous question. Again, look at the link/ether field.

    We could guess that the correct interface on node01 is also eth0 and simply run

    ip link show eth0

    but it's best to be sure.

    Now return to controlplane

    exit
  7. We use Containerd as our container runtime. What is the interface/bridge created by Containerd on this host?

    This is not immediately straight forward.

    ip link show

    Know that

    • Any interface with name beginning eth is a "physical" interface, and represents a network card attached to the host.
    • Interface lo is the loopback, and covers all IP addresses starting with 127. Every computer has this.
    • Any interface with name beginning veth is a virtual network interface used for tunnelling between the host and the pod network. These connect with bridges, and the bridge interface name is listed with their details.

    We can see that for the two veth devices, they are associated with another device in the list cni0, therefore that is the answer.

  8. What is the state of the interface cni0?

    You can see in the output of the previous command that the state field for cni0 is

    UP

  9. If you were to ping google from the controlplane node, which route does it take?

    What is the IP address of the Default Gateway?

    Run

    ip route show default

    and note the output

  10. What is the port the kube-scheduler is listening on in the controlplane node?

    Use the netstat command to look at network sockets used by programs running on the host. There's a lot of output, so we will filter by process name, i.e. kube-scheduler

    netstat -nplt | grep kube-scheduler
    What the netstat options used mean
    • -n - Show IP addresses (don't try to resolve to host names)
    • -p - Show the process names (e.g. kube-scheduler)
    • -l - Include only listening sockets
    • -t - Include only TCP sockets

    Output:

    tcp        0      0 127.0.0.1:10259         0.0.0.0:*               LISTEN      3291/kube-scheduler

    We can see it's listening on localhost, port 10259

  11. Notice that ETCD is listening on two ports. Which of these have more client connections established?

    We use netstat with slightly different options and filter for etcd

    netstat -anp | grep etcd
    What the netstat options used mean
    • -a - Include sockets in all states
    • -n - Show IP addresses (don't try to resolve to host names)
    • -p - Show the process names (e.g. etcd)

    You can see that by far and away, the most used port is 2379.

  12. Information

    That's because 2379 is the port of ETCD to which API server connects to There are multiple concurrent connections so that API server can process multiple etcd operations simultaneously.

    2380 is only for etcd peer-to-peer connectivity when you have multiple controlplane nodes. In this case we don't.