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How to resolve the external IP of a public-facing Service/Ingress

The problem

Since zCompute is not a public DNS registrar (like AWS Route53, GoDaddy, etc.) public-facing Load Balancers (both NLB & ALB) get an external DNS identifier which can't be resolved - only the external IP is resolvable. This is true for both regular cloud and Kubernetes usages, but while regular cloud usage usually work directly with the cloud (either via the web console or AWS API-based tools like Terraform), in the Kubernetes usage case the users might not even be aware of the underline cloud. Because the AWS Load Balancer Controller only provide the public DNS upon service/ingress creation, users are required to manually look for it one way or another.

The alternatives

  1. Login into the zCompute web console, find the Load Balancer resource and fetch the external IP
  2. Use the Symp CLI tool to programatically fetch the external IP - you will need the cloud API endpoint as well as zCompute authentication (username & password)
  3. Use the AWS CLI tool to programatically fetch the external IP - you will need the cloud API endpoint as well as AWS credentials (access & secret keys)
  4. SSH into a Kubernetes node (assuming you have the predefined key-pair) and use the pre-installed AWS CLI tool to programatically fetch the external IP (no need to authenticate as all nodes use an instance profile)
  5. Run a node-shell pod (built-in with OpenLens but you can also deploy it independently) to do the same as #4 from within Kubernetes (requires admin permissions)
  6. Run the AWS CLI docker image (no need for any authentication as it will run on a Kubernetes node which already use an instance profile)

Example for alternative #6

Assuming we have a running service/ingress named wordpress-1700633749 on the wp namespace, we can describe it in order to get the public DNS of the Load Balancer, or we can use such command (replace service with ingress if relevant):

kubectl get service wordpress-1700633749 -n wp -o jsonpath='{.status.loadBalancer.ingress[0].hostname}'

Once we have the public DNS of the Load Balancer (either manually or programmatically), which we will use to populate the PUBLIC_DNS parameter in the below command before running it:

kubectl run -q aws --image amazon/aws-cli --restart=Never --rm -i --env PUBLIC_DNS=elb-ad7071e0-4d9c-4e7d-8478-0dc10241fecd.elb.services.symphony.public \
    --command -- /bin/bash << EOF
        yum install -y -q jq
        aws ec2 describe-network-interfaces \
        --endpoint-url \$(curl -s http://169.254.169.254/openstack/latest/meta_data.json | jq -c -r '.cluster_url')"/api/v2/aws/ec2" \
        --filter Name=addresses.private-ip-address,Values=\$(getent hosts \$(echo "\$PUBLIC_DNS" | cut -d. -f1) | cut -d\  -f1)  \
        --query 'NetworkInterfaces[0].Association.PublicIp' \
        --output text
EOF

This command will do the below:

  • Start a new AWS CLI pod that will be deleted once the execution finishes
  • Install jq in order to parse the internal API endpoint location of the zCompute cluster
  • Find out the private IP of the private DNS equivalent of the public DNS
  • Invoke the AWS CLI command to find the public IP linked with the private IP

The output will be the external IP of the Load Balancer.