IBM Cloud Kubernetes Service clusters are deployed with a ConfigMap (kube-system/ibm-k8s-controller-config) that contains the default managed configuration for application load balancers (ALBs). Occasionally IKS adjusts the ConfigMap values, you can always find the latest version in this repository (see ibm-k8s-controller-config.yaml).
Read more about IBM Cloud Kubernetes Service ALBs in our documentation. Find more details about the possible configuration values in nginx-ingress' documentation.