Freezes an index.
A frozen index has almost no overhead on the cluster (except for maintaining its metadata in memory) and is read-only. Read-only indices are blocked for write operations, such as docs-index_ or force merges. See Frozen indices and Unfreeze index.
Freezing an index will close the index and reopen it within the same API call. This causes primaries to not be allocated for a short amount of time and causes the cluster to go red until the primaries are allocated again. This limitation might be removed in the future.