When an index is shrunk using the shrink APIs, the shrink operation adds
some internal index settings to the shrink index, for example
`index.shrink.source.name|uuid` to denote the source index, as well as
`index.routing.allocation.initial_recovery._id` to denote the node on
which all shards for the source index resided when the shrunken index
was created. However, this presents a problem when taking a snapshot of
the shrunken index and restoring it to a cluster where the initial
recovery node is not present, or restoring to the same cluster where the
initial recovery node is offline or decomissioned. The restore
operation fails to allocate the shard in the shrunken index to a node
when the initial recovery node is not present, and a restore type of
recovery will *not* go through the PrimaryShardAllocator, meaning that
it will not have the chance to force allocate the primary to a node in
the cluster. Rather, restore initiated shard allocation goes through
the BalancedShardAllocator which does not attempt to force allocate a
primary.
This commit fixes the aforementioned problem by not requiring allocation
to occur on the initial recovery node when the recovery type is a
restore of a snapshot. This commit also ensures that the internal
shrink index settings are recognized and not archived (which can trip an
assertion in the restore scenario).
Closes#24257
0e52e3420e