Nomad volume specification capability block

The capability block allows validating that a volume meets the requested capabilities.

id           = "ebs_prod_db1"
namespace    = "default"
name         = "database"
type         = "csi"
plugin_id    = "ebs-prod"
capacity_max = "200G"
capacity_min = "100G"

capability {
  access_mode     = "single-node-reader-only"
  attachment_mode = "file-system"
}

You must provide at least one capability block, and you must provide a block for each capability you intend to use in a job's volume block.

Parameters

• access_mode (string) - Defines whether a volume should be available concurrently. The access_mode and attachment_mode from the volume request must exactly match one of the volume's capability blocks.

  • For CSI volumes the access_mode is required. Can be one of the following:

    • "single-node-reader-only": Jobs can only request the volume with read-only access, and only one node can mount the volume at a time.
    • "single-node-writer": Jobs can request the volume with read/write or read-only access, and only one node can mount the volume at a time.
    • "multi-node-reader-only": Jobs can only request the volume with read-only access, but multiple nodes can mount the volume simultaneously.
    • "multi-node-single-writer": Jobs can request the volume with read/write or read-only access, but the scheduler only allows one allocation to have read/write access. Multiple nodes can mount the volume simultaneously.
    • "multi-node-multi-writer": Jobs can request the volume with read/write or read-only access, and the scheduler allows multiple allocations to have read/write access. Multiple nodes can mount the volume simultaneously.

    Most CSI plugins support only single-node modes. Consult the documentation of the storage provider and CSI plugin.

  • For dynamic host volumes the access_mode is optional. Can be one of the following:

    • "single-node-writer": Jobs can only request the volume with read/write access.
    • "single-node-reader-only": Jobs can only request the volume with read-only access.
    • "single-node-single-writer": Jobs can request either read/write or read-only access, but the scheduler only allows one allocation to have read/write access.
    • "single-node-multi-writer": Jobs can request either read/write or read-only access, and the scheduler allows multiple allocations to have read/write access.

    In the job specification, the default is single-node-writer unless read_only = true, which translates to single-node-reader-only.

• attachment_mode (string) - The storage API used by the volume. One of "file-system" or "block-device". The access_mode and attachment_mode from the volume request must exactly match one of the volume's capability blocks.

  • For CSI volumes the attachment_mode field is required. Most storage providers support "file-system", to mount volumes using the CSI filesystem API. Some storage providers support "block-device", which mounts the volume with the CSI block device API within the container.

  • For dynamic host volumes the attachment_mode field is optional and defaults to "file-system".

Example

This examples shows a volume that must satisfy multiple capability requirements.

capability {
  access_mode     = "single-node-reader-only"
  attachment_mode = "file-system"
}

capability {
  access_mode     = "single-node-writer"
  attachment_mode = "file-system"
}