Volume - Uniac

A volume is durable storage with a project-scoped identity. Its data and lifetime are independent of the service holding it.

Required and optional configuration

A singleton service can attach one volume. An attachment requires:

Field	Required	Meaning
`name`	Yes	Local volume name matching `^[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?$`.
`size_gb`	Yes	Size in GB when the volume is created: a number from 1 to 4096 after truncation toward zero. Later deployments declare the same size, as Lifecycle describes.
`mount_path`	Yes	Absolute path other than `/`, with no `.` or `..` segments, repeated slashes, or trailing slash, outside `/proc`, `/sys` and `/dev`, and other than `/etc/resolv.conf`.

The resulting project-scoped name is <service>.<name>, up to 127 characters, where <service> is the name of the deployment declaration that instantiates the definition.

YAML composition example

In YAML composition, a volume declaration is a mapping with name, size_gb, and mount_path inside the service definition’s optional volumes list. Omitting volumes, setting it to null, or using [] declares no volume. The singleton cache service mounts cache.data at /data. Redis writes its append-only persistence files there, and the volume retains them across container replacement.

resources:
  cache-code:
    type: singleton
    image: redis:7-alpine
    start_command: redis-server --appendonly yes
    volumes:
      - name: data
        size_gb: 1
        mount_path: /data
  cache:
    type: deployment
    from: cache-code

In the generated description, the declaration is one volume object with the scoped name, size_gb, and mount_path.

Lifecycle

Declaring a new volume name provisions storage, and declaring an existing unattached volume attaches it; each volume has one holder at a time. Redeploying with the same volume name reuses its data, including when its mount path changes. Removing the volume declaration on redeploy detaches it; deleting the service also detaches its volume and preserves its data. A volume keeps the size it was created with. A deployment that declares another size_gb for an existing volume stops the singleton’s running replica and then fails; the service stays stopped until a deployment declares the original size. A volume’s state distinguishes attachment to a service from an unattached volume whose data is retained. Transitional states include provisioning, attaching, detaching, and deleting. A fresh volume contains lost+found. A volume is deleted once no service holds it. Deletion requires name confirmation and destroys stored data.

​Required and optional configuration

​YAML composition example

​Lifecycle

Required and optional configuration

YAML composition example

Lifecycle