With new logstash ES hosts racked and installed (in T240881 and T240882), it's time to configure an SSD indexing tier for the ELK7 cluster.
Here's a checklist in rough sequence aiming to do this without unwanted shard relocation.
[x] Add an ES node attribute to "tag" the backing storage type for a given host.
* https://gerrit.wikimedia.org/r/#/c/operations/puppet/+/578653/
[] Prepare an ELK7 logstash template with a routing allocation rule to ensure new indices are written to HDD (initially) using the above mentioned attribute.
* https://gerrit.wikimedia.org/r/#/c/operations/puppet/+/579338/
[] Manually set the routing allocation for all existing indices to require `"disktype":"hdd"`.
[] Add new SSD hosts to ES cluster.
* https://gerrit.wikimedia.org/r/#/c/operations/puppet/+/579340/
[] Deploy an updated logstash template with routing allocation requiring `"disktype":"ssd"` for new indices.
[] Add a curator job (or similar) to require `"disktype":"hdd"` 7 days(?) after creation.
* https://gerrit.wikimedia.org/r/#/c/operations/puppet/+/579422/