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11-pod-network-routes.md

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Provisioning Pod Network Routes

Pods scheduled to a node receive an IP address from the node's Pod CIDR range. At this point pods can not communicate with other pods running on different nodes due to missing network routes.

In this lab you will create a route for each worker node that maps the node's Pod CIDR range to the node's internal IP address.

There are other ways to implement the Kubernetes networking model.

The Routing Table

On each worker node, add the following routes:

WARNING: don't add the route associated to the POD CIDR for the current node (ex: don't add the 10.200.0.0/24 route if you are on the worker-0 node).

ip route add 10.200.0.0/24 via 172.16.0.20 # Don't add on worker-0
ip route add 10.200.1.0/24 via 172.16.0.21 # Don't add on worker-1
ip route add 10.200.2.0/24 via 172.16.0.22 # Don't add on worker-2

Don't take care of the RTNETLINK answers: File exists message, it appears just when you try to add an existing route, not a real problem.

List the routes in the kubernetes-the-hard-way VPC network:

ip route

Output (example for worker-0):

default via 172.16.0.1 dev ens19 proto static 
10.200.1.0/24 via 172.16.0.21 dev ens19 
10.200.2.0/24 via 172.16.0.22 dev ens19 
172.16.0.0/24 dev ens19 proto kernel scope link src 172.16.0.20

To make it persistent (if reboot), you need to edit your network configuration (depends on your Linux distribution).

Example for Ubuntu 18.04 and higher:

vi /etc/netplan/00-installer-config.yaml

Content (example for worker-0, don't specify the POD CIDR associated with the current node):

network:
  version: 2
  ethernets:
    ens18:
      dhcp4: true
      dhcp4-overrides:
        use-routes: false
    ens19:
      dhcp4: no
      addresses:
        - 172.16.0.20/24
      gateway4: 172.16.0.1
      nameservers:
        addresses:
          - 8.8.8.8
          - 8.8.4.4
      routes:
        - to: 172.16.0.0/24
          via: 172.16.0.1
          scope: link
        - to: 10.200.1.0/24
          via: 172.16.0.21
        - to: 10.200.2.0/24
          via: 172.16.0.22

Next: Deploying the DNS Cluster Add-on