Get count of spare IPs left on each EKS worker node, sorted from oldest to newest node

get-node-ips.sh

#!/bin/bash

REGION=us-east-1

# Get a list of all the nodes in the cluster
NODES=$(kubectl get nodes  --sort-by=.metadata.creationTimestamp -o=jsonpath='{.items[*].metadata.name}')

K8S_NODES_DATA=$(kubectl get no -ojson)

# Create a temporary file to store combined output
tempfile=$(mktemp)

# Create and store a list of ALL the pods running in the cluster
ALL_PODS=$(kubectl get pods -o wide --all-namespaces)

# Get a list of AWS instance IDs
# To be used as input for `aws describe-instances`
AWS_INSTANCE_ID_LIST=$(echo $K8S_NODES_DATA | jq '.items[].spec.providerID' | tr -d '"')
AWS_INSTANCE_ID_LIST=$(echo $AWS_INSTANCE_ID_LIST | sed 's/aws:\/\/\/[a-z]*-[a-z]*-[0-9][a-z]\///g')

# Prepare aws output for all instances
AWS_OUTPUT=$(aws ec2 describe-instances \
    --instance-ids $AWS_INSTANCE_ID_LIST \
    --output json \
    --region $REGION)

echo -e "node\tallowed_pods\trunning_pods\tattached_ips\tunused_ips" >>"$tempfile"

# Iterate over each node
for node in $NODES; do
    allowed_pods=($(echo $K8S_NODES_DATA | jq ".items[] | select(.metadata.name == \"$node\")" | jq '.status.allocatable.pods' | tr -d '"'))

    # Get no. of pods running on the node
    running_pods=$(echo "$ALL_PODS" | grep $node | wc -l)

    # Get count of allocated IPs (it should match IPs seen in AWS EC2 console)
    attached_ips=($(echo $AWS_OUTPUT | jq ".Reservations[].Instances[] | select(.PrivateDnsName == \"$node\")" | jq '.NetworkInterfaces[].PrivateIpAddresses[].PrivateIpAddress' | wc -l))

    # Subtract above to get unused/available IPs
    unused_ips=$(expr $attached_ips - $running_pods)

    echo -e "$node\t$allowed_pods\t$running_pods\t$attached_ips\t$unused_ips" >>"$tempfile"
done

# Print the combined output in a table format using column command
column -t -s $'\t' "$tempfile"

# echo "$tempfile"
# Remove the temporary file
# rm "$tempfile"

Before running the script, make sure to point kube context to the intended cluster.

Sample output should look something like this -

node                          allowed_pods  running_pods  attached_ips  unused_ips
ip-10-4-xx-xxx.ec2.internal   58                  24      33            9
ip-10-4-xxx-xxx.ec2.internal  234                 81      94            13
ip-10-4-aa-aa.ec2.internal    58                  17      28            11
ip-10-4-bb-bbb.ec2.internal   58                  29      45            16