In this scenario, you need to ensure that there is an additional 10% capacity of Pods available to handle traffic when nodes are drained. By increasing the replica count by 10%, you provide a buffer to maintain high availability during node drains. This approach meets the high-availability requirement by ensuring sufficient Pods remain available during upgrades or disruptions.
Options like Pod Disruption Budget (PDB) with a minAvailable value of 10% do not directly increase the Pod count but rather set a threshold for the minimum number of available Pods, which could result in reduced serving capacity during node drains if the replica count itself is not increased.

https://cloud.google.com/kubernetes-engine/docs/concepts/ingress
In GKE, an Ingress object defines rules for routing HTTP(S) traffic to applications running in a cluster. An Ingress object is associated with one or more Service objects, each of which is associated with a set of Pods. To learn more about how Ingress exposes applications using Services, see Service networking overview.
When you create an Ingress object, the GKE Ingress controller creates a Google Cloud HTTP(S) Load Balancer and configures it according to the information in the Ingress and its associated Services.

Pub/Sub is a messaging service that allows you to decouple microservices and other applications. It is a good choice for this use case because it is scalable, reliable, and easy to use.

Attestation: By creating an attestation for container images that have successfully passed regression tests, you can enforce deployment policies that only allow images with valid attestations to be deployed to your GKE clusters.
Integration with Binary Authorization: This approach directly integrates with Binary Authorization, allowing it to enforce the deployment policy based on the attestations created during the Cloud Build pipeline.
Control and Security: This method ensures that only thoroughly tested and verified images are deployed, enhancing the security and reliability of your applications.
Options "Deploy Voucher Server and Voucher Client components. After a container image has passed the regression tests, run Voucher Client as a step in the Cloud Build pipeline" and "Set the Pod Security Standard level to Restricted for the relevant namespaces. Digitally sign the container images that have passed the regression tests as a step in the Cloud Build pipeline" do not specifically leverage the attestation mechanism necessary for Binary Authorization. Option
"Create an attestor and a policy. Run a vulnerability scan to create an attestation for the container image as a step in the Cloud Build pipeline" focuses on vulnerability scanning, which, while important, does not fulfill the requirement of ensuring that only tested images are deployed.