IBM Cloud Transit Gateway is the correct choice because it is specifically designed to connect multiple Virtual Private Clouds (VPCs) and classic infrastructure (like VMware Solutions) into a single, simplified network. It provides centralized routing, security, and control, which is essential for maintaining consistent network policies and security during a hybrid migration scenario. While the other services are valuable, they address specific aspects (compliance auditing, physical connectivity, encryption) rather than the core network policy and connectivity challenge presented.

IBM Cloud Internet Services (CIS) with its Global Load Balancer (GLB) is the premier solution for scalable, highly available public ingress. The GLB can direct traffic to a pool of origins (the VPC instances) spread across multiple zones within a region. It provides health checks, automatic failover, and DDoS protection. A single public gateway is not a load balancer. A VPN gateway is for private access. Managing multiple VPC load balancers with manual DNS is complex and less resilient than a managed global service.

Attaching a secondary block storage (Volume) is the standard solution for this need. VPC Block Storage volumes are persistent, independent of the virtual server instance’s lifecycle, can be attached/detached, and support dynamic capacity expansion. Local SSD is not persistent (data is lost if the instance is stopped or fails). Object Storage is for unstructured data and is not a block-level solution. File Storage is a good choice for shared file access (NFS) but for a single instance’s dedicated block storage, a secondary volume is more direct and typically lower latency.

The ‘Customer-managed encryption’ feature for VPC Block Storage is the direct mechanism that allows you to use your own root keys from a supported key management service (like IBM Cloud Hyper Protect Crypto Services or Key Protect) to encrypt your boot and data volumes. This satisfies the requirement that IBM does not manage the encryption keys. Secure Boot ensures image integrity. Private Endpoints enhance security but don’t enable the key management model. BYOIP is for IP address management.

Using a bastion host (or NAT gateway instance) in a public subnet is a classic and secure pattern for providing outbound internet access to private instances. The private instances route traffic through the bastion, which performs Source Network Address Translation (SNAT). This avoids exposing the private instances directly to the internet. Attaching a public gateway or assigning floating IPs defeats the purpose of a private subnet. A VPN to on-premises is overly complex and introduces latency for a simple update task.

Security Groups are stateful, virtual firewalls that are attached to network interfaces (instances). They are the ideal tool for defining instance-level, granular rules like “allow traffic from the application subnet on port 3306.” ACLs are stateless and operate at the subnet level, which is less granular for this specific inter-tier communication requirement. NAT rules translate addresses. Routing tables determine the path of traffic, not whether it is permitted.

IBM Cloud Schematics is a fully managed service that allows you to use Terraform HCL templates to create, manage, and destroy cloud resources. It provides a native IBM Cloud environment for running Terraform, handling state files, and managing workspaces, which is ideal for automated, consistent environment provisioning. While you can use the open-source Terraform CLI with the IBM Provider, Schematics offers a managed, integrated solution within the IBM Cloud ecosystem, reducing operational overhead.

IBM Cloud Transit Gateway with its global routing capability is the simplest and most direct service for creating private connectivity between VPCs in different regions. It establishes a private, IBM backbone connection, avoiding the public internet. Direct Link is for connecting to on-premises data centers, not for inter-VPC connectivity. A site-to-site VPN works but is more complex to configure and manage than a fully-managed Transit Gateway connection.

The profile family (e.g., Balanced, Compute, Memory, GPU) is the primary selector. It defines the core resource ratio and intended use case. For a general-purpose workload, a ‘balanced’ family profile (like bx2) is typically the correct starting point, offering a good mix of vCPU and memory. The zone affects availability but not profile characteristics. Dedicated hosts are for compliance/ licensing, not performance tuning. The generation is important (newer is often better), but you first choose the family that matches your workload type.

IBM Cloud Transit Gateway is the correct choice because it is specifically designed to connect multiple Virtual Private Clouds (VPCs) and classic infrastructure (like VMware Solutions) into a single, simplified network. It provides centralized routing, security, and control, which is essential for maintaining consistent network policies and security during a hybrid migration scenario. While the other services are valuable, they address specific aspects (compliance auditing, physical connectivity, encryption) rather than the core network policy and connectivity challenge presented.0