To configure a secure multi-tenant platform on GKE where each customer can only access their own blog without affecting others, deploying a namespace per tenant and using Network Policies in each blog deployment is the most effective approach. This method provides both logical separation of resources and network isolation.

• Option A (Enable Application-layer Secrets) is incorrect because it focuses on protecting secrets rather than isolating tenants.
• Option C (Use GKE Audit Logging) is incorrect as it is a reactive measure for identifying malicious activities, not a proactive isolation strategy.
• Option D (Build a custom image and use Binary Authorization) is incorrect because it ensures the integrity of images but does not provide tenant isolation.