Key Considerations

Following are the key factors to deploy the dedicated host:

• The solution supports deployment of both static and dynamic compute nodes exclusively on dedicated hosts.

• There is no separate parameter to specify the dedicated host profile. The dedicated host family is automatically derived from the static_compute_instances parameter. For example, if the compute nodes use a bx2 profile, the dedicated hosts will be provisioned from the bx2 family.

• The current solution supports a single instance profile type from any of the supported families: bx2, cx2, mx2, third-generation, and so on.

For more information, go to Profiles.

Before you begin

Before you begin, make sure to complete the steps from Before you begin deploying topic.

Benefits

Following are the benefits of a dedicated host:

• Consistent and High Performance – Ideal for long-running workloads with demanding performance needs.

• Enhanced Workload Management – Provides better control over virtual server instance placement and resource allocation.

• High Security and Compliance – Ensures physical isolation of workloads, making it suitable for compliance-driven industries with strict data isolation and residency requirements.

Enabling a Dedicated Host

To enable a dedicated host, set the enable_dedicated_host parameter to true (default: false). Once enabled, all the static and dynamic worker nodes are automatically attached to the same dedicated host.

For more information about dedicated host, go to Creating dedicated hosts and groups.

Limitations

1. Single Profile Requirement

   • When enable_dedicated_host is set to true, you must specify only one profile in static_compute_instances parameter.

   • If more than one profile is provided, an error is displayed:

   Error Example:

   Error: Invalid value for variable
   │
   │ on userinput.auto.tfvars line 21:
   │ 21: static_compute_instances = [{
   │ profile = "bx2-4x16"
   │ count   = 1
   │ image   = "hpc-lsf-fp15-compute-rhel810-v4"
   │ },
   | {
   │ profile = "cx2-2x4"
   │ count   = 2
   │ image   = "hpc-lsf-fp15-compute-rhel810-v4"
   | }]
   ├────────────────
   │     │ var.enable_dedicated_host is true
   │     │ var.static_compute_instances is list of object with 2 elements
   │ 
   │When dedicated hosts are enabled, static_compute_instances must contain only a single instance profile entry.   Multiple profile entries are not supported, even if the profiles belong to the same VSI family.
   │ 
   │ This was checked by the validation rule at variables.tf:324,3-13.
   

2. Supported Profiles

   If a single profile from bx2, cx2, mx2, cx2d, mx2d, or bx2d is specified, then the dedicated host is created from the same family and all the worker nodes are assigned to it.

3. Third-Generation Profile Limitation

   • Third-generation profiles like mx3d, cx3d, and bx3d are only available in specific regions (Dallas, Frankfurt, Toronto, Madrid).

   • Deploying an unsupported profile in a different region results in a failure during the planning or early deployment stage.

   Error Example:

   If a profile "bx3d" is provided on us-east, then the build fails at planning or early stage of deployment stating that this profile is not supported.

   Error: Invalid index
   │
   │ on locals.tf line 316, in locals:
   │ 316: dh_profile = var.enable_dedicated_host ? local.dh_profiles[local.dh_profile_index] : null
   │ ├────────────────
   │ │ local.dh_profile_index is "Profile class bx3d for dedicated hosts does not exist in us-east.  Check available class with ibmcloud target -r us-east; ibmcloud is dedicated-host-profiles and retry with another static_compute_instances."
   │ │ local.dh_profiles is empty tuple
   │
   │ The given key does not identify an element in this collection value: a number is required.
   

4. Spot Instances and Dedicated hosts cannot be used together

The solution does not support deployments where both enable_spot_instances and enable_dedicated_host are set to true. To use dedicated hosts, Spot Instances must be disabled, and vice versa.

**Error Example:**

```console
│ Error: Invalid value for variable
│ 
│ on userinput.auto.tfvars line 27:
│ 27: dynamic_compute_instances = [
│ {
│ profile = "bxf-2x8"
│ count   = 500
│ image   = "hpc-lsf-fp15-compute-rhel810-v4"
│ enable_spot_instances = true
│ }
│ ]
│ ├────────────────
│ │ var.dynamic_compute_instances is list of object with 1 element
│ │ var.enable_dedicated_host is true
│ 
│ Spot instances are not supported with dedicated hosts. When enable_spot_instances is true, enable_dedicated_host must be false.
│ 
│ This was checked by the validation rule at variables.tf:392,3-13.

When a dedicated host is enabled, the resource connector templates are automatically updated to include the host ID, allowing dynamic nodes to join.