Allow to configure the base VPC CIDR

cluster/aws/options.md

@@ -141,4 +141,13 @@ export MASTER_IP_RANGE="100.65.0.0/24"
 export CLUSTER_IP_RANGE="100.66.0.0/16"
 ```
 
+**KUBE_VPC_CIDR_BASE**
+
+By default `kube-up.sh` will create a VPC with CIDR 172.20.0.0/16. `KUBE_VPC_CIDR_BASE` allows to configure
+this CIDR. For example you may choose to use `172.21.0.0/16`:
+
+```
+export KUBE_VPC_CIDR_BASE=172.21
+```
+
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cluster/aws/util.sh

@@ -102,7 +102,7 @@ export AWS_DEFAULT_OUTPUT=text
 AWS_CMD="aws ec2"
 AWS_ASG_CMD="aws autoscaling"
 
-VPC_CIDR_BASE=172.20
+VPC_CIDR_BASE=${KUBE_VPC_CIDR_BASE:-172.20}
 MASTER_IP_SUFFIX=.9
 VPC_CIDR=${VPC_CIDR_BASE}.0.0/16
 SUBNET_CIDR=${VPC_CIDR_BASE}.0.0/24