Before we configure EKS, we need to enable secondary CIDR blocks in your VPC and make sure they have proper tags and route table configurations
There are restrictions on the range of secondary CIDRs you can use to extend your VPC. For more info, see IPv4 CIDR Block Association Restrictions
You can use below commands to add 100.64.0.0/16 to your EKS cluster VPC. Please note to change the Values parameter to EKS cluster name if you used different name than eksctl-eksworkshop
VPC_ID=$(aws ec2 describe-vpcs --filters Name=tag:Name,Values=eksctl-eksworkshop* --query 'Vpcs[].VpcId' --output text)
aws ec2 associate-vpc-cidr-block --vpc-id $VPC_ID --cidr-block 100.64.0.0/16
Next step is to create subnets. Before we do this step, let’s check how many subnets we are consuming. You can run this command to see EC2 instance and AZ details
aws ec2 describe-instances --filters "Name=tag-key,Values=eks:cluster-name" "Name=tag-value,Values=eksworkshop*" --query 'Reservations[*].Instances[*].[PrivateDnsName,Tags[?Key==`eks:nodegroup-name`].Value|[0],Placement.AvailabilityZone,PrivateIpAddress,PublicIpAddress]' --output table
I have 3 instances and using 3 subnets in my environment. For simplicity, we will use the same AZ’s and create 3 secondary CIDR subnets but you can certainly customize according to your networking requirements. Remember to change the AZ names according to your environment
export AZ1=us-east-2a
export AZ2=us-east-2b
export AZ3=us-east-2c
CGNAT_SNET1=$(aws ec2 create-subnet --cidr-block 100.64.0.0/19 --vpc-id $VPC_ID --availability-zone $AZ1 --query 'Subnet.SubnetId' --output text)
CGNAT_SNET2=$(aws ec2 create-subnet --cidr-block 100.64.32.0/19 --vpc-id $VPC_ID --availability-zone $AZ2 --query 'Subnet.SubnetId' --output text)
CGNAT_SNET3=$(aws ec2 create-subnet --cidr-block 100.64.64.0/19 --vpc-id $VPC_ID --availability-zone $AZ3 --query 'Subnet.SubnetId' --output text)
Next step is to add Kubernetes tags on newer Subnets. You can check these tags by querying your current subnets
aws ec2 describe-subnets --filters Name=cidr-block,Values=192.168.0.0/19 --output text
Output shows similar to this
Here are the commands to add tags to both the subnetsaws ec2 create-tags --resources $CGNAT_SNET1 --tags Key=eksctl.cluster.k8s.io/v1alpha1/cluster-name,Value=eksworkshop-eksctl
aws ec2 create-tags --resources $CGNAT_SNET1 --tags Key=kubernetes.io/cluster/eksworkshop-eksctl,Value=shared
aws ec2 create-tags --resources $CGNAT_SNET1 --tags Key=kubernetes.io/role/elb,Value=1
aws ec2 create-tags --resources $CGNAT_SNET2 --tags Key=eksctl.cluster.k8s.io/v1alpha1/cluster-name,Value=eksworkshop-eksctl
aws ec2 create-tags --resources $CGNAT_SNET2 --tags Key=kubernetes.io/cluster/eksworkshop-eksctl,Value=shared
aws ec2 create-tags --resources $CGNAT_SNET2 --tags Key=kubernetes.io/role/elb,Value=1
aws ec2 create-tags --resources $CGNAT_SNET3 --tags Key=eksctl.cluster.k8s.io/v1alpha1/cluster-name,Value=eksworkshop-eksctl
aws ec2 create-tags --resources $CGNAT_SNET3 --tags Key=kubernetes.io/cluster/eksworkshop-eksctl,Value=shared
aws ec2 create-tags --resources $CGNAT_SNET3 --tags Key=kubernetes.io/role/elb,Value=1
As next step, we need to associate three new subnets into a route table. Again for simplicity, we chose to add new subnets to the Public route table that has connectivity to Internet Gateway
SNET1=$(aws ec2 describe-subnets --filters Name=cidr-block,Values=192.168.0.0/19 --query 'Subnets[].SubnetId' --output text)
RTASSOC_ID=$(aws ec2 describe-route-tables --filters Name=association.subnet-id,Values=$SNET1 --query 'RouteTables[].RouteTableId' --output text)
aws ec2 associate-route-table --route-table-id $RTASSOC_ID --subnet-id $CGNAT_SNET1
aws ec2 associate-route-table --route-table-id $RTASSOC_ID --subnet-id $CGNAT_SNET2
aws ec2 associate-route-table --route-table-id $RTASSOC_ID --subnet-id $CGNAT_SNET3