To establish a reliable, cloud-native, and scalable process for updating nodes in your GKE clusters, configuring node auto-upgrades within designated maintenance windows is the most effective approach.​

Option A: Migrating to a self-managed Kubernetes environment would increase operational overhead and complexity, as your team would be responsible for managing the entire infrastructure, including patching and updates. This contradicts the goal of adopting a cloud-first strategy and does not inherently provide a more reliable update process.​

Option B: Developing custom scripts for patch management introduces potential risks and maintenance burdens. Ensuring the reliability, security, and scalability of such scripts can be challenging, and this approach may not align with best practices for managing GKE environments.​

Option C: Scheduling daily reboots does not guarantee that nodes will apply the latest patches or updates. Without a mechanism to manage and apply updates, reboots alone are insufficient to maintain node security and compliance.​

Option D: Configuring node auto-upgrades ensures that GKE automatically keeps your nodes up-to-date with the latest stable versions, reducing the risk of missed critical patches. By setting maintenance windows, you can control when these upgrades occur, minimizing disruptions to your workloads. This approach leverages GKE's managed services to maintain security and compliance efficiently.​

Therefore, Option D is the optimal solution, as it aligns with a cloud-first strategy and leverages GKE's native capabilities to automate and schedule node updates effectively.​