Camera Snapshot: Rendering error

Hello dear community,

I am not a newbie but have not much experience with data templates.
Got two cameras that i want to save snapshots with time and entity name.

The following is working in developer mode but not in a Script i am writing. The script throws this error:

[140602836889024] Error rendering data template: UndefinedError: 'entity_id' is undefined

The working code in developer mode:

service: camera.snapshot
data:
  filename: >-
    www/snapshots/snapshot_{{ entity_id.name }}_{{
    now().strftime("%Y%m%d-%H%M%S") }}.jpg
target:
  entity_id:
    - camera.front_door_cam
    - camera.living_cam

The above is working ok and saves two snapshots to the configured folder.