kubernetes-the-hard-way/docs/11-pod-network-routes.md

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

In this section you will gather the information required to create routes in the kubernetes-the-hard-way VPC network.

Print the internal IP address and Pod CIDR range for each worker instance:

GCP

for instance in worker-0 worker-1 worker-2; do
  gcloud compute instances describe ${instance} \
    --format 'value[separator=" "](networkInterfaces[0].networkIP,metadata.items[0].value)'
done

AWS

VPC_ID="$(aws ec2 describe-vpcs \
  --filters Name=tag-key,Values=kubernetes.io/cluster/kubernetes-the-hard-way \
  --profile kubernetes-the-hard-way \
  --query 'Vpcs[0].VpcId' \
  --output text)"

for i in 0 1 2; do
  instance_id="$(aws ec2 describe-instances \
    --filters \
      Name=vpc-id,Values="$VPC_ID" \
      Name=tag:Name,Values="worker-$i" \
    --profile kubernetes-the-hard-way \
    --query 'Reservations[0].Instances[0].InstanceId' \
    --output text)"

  instance_ip="$(aws ec2 describe-instances \
    --instance-ids "$instance_id" \
    --profile kubernetes-the-hard-way \
    --query 'Reservations[0].Instances[0].PrivateIpAddress' \
    --output text)"

  instance_ud="$(aws ec2 describe-instance-attribute \
    --instance-id "$instance_id" \
    --attribute userData \
    --profile kubernetes-the-hard-way \
    --query UserData.Value \
    --output text|base64 --decode)"

  pod_cidr="$(echo "$instance_ud"|tr '|' '\n'|grep '^pod-cidr='|cut -d= -f2)"

  echo "$instance_ip $pod_cidr"
done

output

10.240.0.20 10.200.0.0/24
10.240.0.21 10.200.1.0/24
10.240.0.22 10.200.2.0/24

Routes

Create network routes for each worker instance:

GCP

for i in 0 1 2; do
  gcloud compute routes create kubernetes-route-10-200-${i}-0-24 \
    --network kubernetes-the-hard-way \
    --next-hop-address 10.240.0.2${i} \
    --destination-range 10.200.${i}.0/24
done

AWS

ROUTE_TABLE_ID="$(aws ec2 describe-route-tables \
  --filters \
    Name=vpc-id,Values="$VPC_ID" \
    Name=tag-key,Values=kubernetes.io/cluster/kubernetes-the-hard-way \
  --profile kubernetes-the-hard-way \
  --query 'RouteTables[0].RouteTableId' \
  --output text)"

for i in 0 1 2; do
  instance_id="$(aws ec2 describe-instances \
    --filters \
      Name=vpc-id,Values="$VPC_ID" \
      Name=tag:Name,Values="worker-$i" \
    --profile kubernetes-the-hard-way \
    --query 'Reservations[0].Instances[0].InstanceId' \
    --output text)"

  instance_ud="$(aws ec2 describe-instance-attribute \
    --instance-id "$instance_id" \
    --attribute userData \
    --profile kubernetes-the-hard-way \
    --query UserData.Value \
    --output text|base64 --decode)"

  pod_cidr="$(echo "$instance_ud"|tr '|' '\n'|grep '^pod-cidr='|cut -d= -f2)"

  aws ec2 create-route \
    --route-table-id "$ROUTE_TABLE_ID" \
    --destination-cidr-block "$pod_cidr" \
    --instance-id "$instance_id" \
    --profile kubernetes-the-hard-way
done

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

GCP

gcloud compute routes list --filter "network: kubernetes-the-hard-way"

AWS

aws ec2 describe-route-tables \
  --route-table-id "$ROUTE_TABLE_ID" \
  --profile kubernetes-the-hard-way \
  --query 'RouteTables[0].Routes[]|sort_by(@, &DestinationCidrBlock)[].[InstanceId,DestinationCidrBlock,GatewayId]' \
  --output table

output

GCP

NAME                            NETWORK                  DEST_RANGE     NEXT_HOP                  PRIORITY
default-route-236a40a8bc992b5b  kubernetes-the-hard-way  0.0.0.0/0      default-internet-gateway  1000
default-route-df77b1e818a56b30  kubernetes-the-hard-way  10.240.0.0/24                            1000
kubernetes-route-10-200-0-0-24  kubernetes-the-hard-way  10.200.0.0/24  10.240.0.20               1000
kubernetes-route-10-200-1-0-24  kubernetes-the-hard-way  10.200.1.0/24  10.240.0.21               1000
kubernetes-route-10-200-2-0-24  kubernetes-the-hard-way  10.200.2.0/24  10.240.0.22               1000

AWS

----------------------------------------------------------
|                   DescribeRouteTables                  |
+---------------------+-----------------+----------------+
|  None               |  0.0.0.0/0      |  igw-116a3177  |
|  i-0d173dd08280c9f52|  10.200.0.0/24  |  None          |
|  i-0a4ae7e79b0bc3cc9|  10.200.1.0/24  |  None          |
|  i-0a424b69034b9068f|  10.200.2.0/24  |  None          |
|  None               |  10.240.0.0/24  |  local         |
+---------------------+-----------------+----------------+

Next: Deploying the DNS Cluster Add-on