This setting is only used by the shrink action.

action: shrink
description: >-
  Shrink selected indices on the node with the most available space.
  Prepend target index names with 'foo-' and append a suffix of '-shrink'
  shrink_node: DETERMINISTIC
  shrink_prefix: 'foo-'
  shrink_suffix: '-shrink'
  - filtertype: ...

The default value for this setting is -shrink.

The value of this setting will be appended to target index names. If the source index were index, and the shrink_prefix were foo-, and the shrink_suffix were -shrink, the resulting target index name would be foo-index-shrink.