I have two indices in my setup.
marimba-000001 & marimba-000002 with alias marimba.
Before applying to ILM
I created a policy with rollover action. Then, on the existing template, I added that policy, added an alias, and created an index with a write index.
PUT marimba-000001 { "aliases": { "marimba": { "is_write_index": true } } }
And I reindex the data from the existing index to this marimba-000001 index. And the policy started running. I took a snapshot of the rolled over index and tried restoring it, but it failed after some time without throwing an error in the Kibana dashboard or even getting any logs regarding that.