Databricks Apps **NOT** mapping volume to app runtime

[Escoto]

Describe the issue

Hi I would appreciate your help debugging this problem i found while working with Databricks Apps. I am deploying an App that needs to read and write from a Volume.

Everything looks right in the deployment, but in the runtime seems like Volumes are not being attached/mapped.

In Databricks UI everything seems correctly configured, when getting configs with the CLI, these also seems to be right too.

Configuration

Note. I am summarizing the config - cant fit the whole thing here.

on Databricks resources (bundle config)

resources:
  apps:
    my-app:
      resources:
        - name: GXP_PROJECTS_VOLUME
          description: "Unity Catalog Volume for project documents"
          uc_securable:
            permission: WRITE_VOLUME
            securable_full_name: testing_dev_01.functional_testing.source_data
            securable_type: VOLUME

on /app/app.yaml (app specific config)

command: ...
env:
  - name: VOLUME_BASE_PATH
    valueFrom: GXP_PROJECTS_VOLUME

Based on Debug Logs later, you can see these configs result in the expected behavior. Yet, inside the app
Running os.system('df -h'), you can see there is no Volumes mount:

Filesystem              Size  Used Avail Use% Mounted on
overlay                 190G   18G  162G  10% /
tmpfs                    64M     0   64M   0% /dev
tmpfs                   7.7G     0  7.7G   0% /sys/fs/cgroup
overlayroot             190G   18G  162G  10% /databricks/runtime-secrets
/dev/mapper/rw-encrypt  190G   18G  162G  10% /databricks/customer-logs
overlayroot             190G   18G  162G  10% /dev/termination-log
shm                      64M     0   64M   0% /dev/shm
tmpfs                   7.7G     0  7.7G   0% /proc/acpi
tmpfs                   7.7G     0  7.7G   0% /proc/scsi
tmpfs                   7.7G     0  7.7G   0% /sys/firmware

Steps to reproduce the behavior

Please list the steps required to reproduce the issue, for example:

1. Run databricks bundle deploy
2. Run databricks bundle run my-app
3. Deployment looks right

• Resources created as expected
  • Volume appears in resources section in the app
• SP has CAN READ + CAN WRITE in Volume... CAN USE in Catalog and Schema

4. When trying to create a directory directory TEST:

project_dir = Path(os.environ["VOLUME_BASE_PATH"]) / "TEST"
print(project_dir) # logs: /Volumes/testing_dev_01/functional_testing/source_data/TEST 
project_dir.mkdir() # logs: FileNotFoundError: [Errno 2] No such file or directory: /Volumes/testing_dev_01/functional_testing/source_data/TEST'

Expected Behavior

Volumes are reachable

Actual Behavior

Volumes are not reachable

OS and CLI version

• Databricks CLI v0.294.0

Debug Logs

/> databricks apps get my-app --output json

{
  "active_deployment": {
    "create_time":"2026-03-13T10:19:02Z",
    "creator":"{..ME..}",
    "deployment_artifacts": {
      "source_code_path":"/Workspace/Users/{..SP..}/src/01f11ec60ed11fbbbe45eea93d19588d"
    },
    "deployment_id":"01f11ec60ed11fbbbe45eea93d19588d",
    "mode":"SNAPSHOT",
    "source_code_path":"/Workspace/Users/{..ME..}/.bundle/{..BUNDLE..}/dev_01/files/app",
    "status": {
      "message":"App started successfully",
      "state":"SUCCEEDED"
    },
    "update_time":"2026-03-13T10:19:38Z"
  },
  "app_status": {
    "message":"App has status: App is running",
    "state":"RUNNING"
  },
  "compute_size":"MEDIUM",
  "compute_status": {
    "message":"App compute is running.",
    "state":"ACTIVE"
  },
  "create_time":"2026-03-13T09:49:43Z",
  "creator":"{..ME..}",
  "default_source_code_path":"/Workspace/Users/{..ME..}/.bundle/{..BUNDLE..}/dev_01/files/app",
  "description":"",
  "id":"{..SP..}",
  "name":"{..APP NAME..}",
  "oauth2_app_client_id":"{..oath2..}",
  "oauth2_app_integration_id":"{..oath2..}",
  "resources": [
    {
      "description":"Unity Catalog Volume for project documents",
      "name":"GXP_PROJECTS_VOLUME",
      "uc_securable": {
        "permission":"WRITE_VOLUME",
        "securable_full_name":"testing_dev_01.functional_testing.source_data",
        "securable_type":"VOLUME"
      }
    }
  ],
  "service_principal_client_id":"{..SP..}",
  "service_principal_id":1234567890,
  "service_principal_name":"app-2hhy48 {..APP NAME..}",
  "update_time":"2026-03-13T10:19:02Z",
  "updater":"{..ME..}",
  "url":"https://{..APP NAME..}-1497042897853922.aws.databricksapps.com"
}

[Escoto]

any help? :(