Index routing settings

I'm trying to implement hot-cold architecture (https://www.elastic.co/blog/hot-warm-architecture)

Instead of using the curl to update the index setting, I want to use elasticsearch.yml to update the 'index.routing.allocation.require.box_type'

this isn't working..

what is the syntax for this?

That's not an ideal situation, as any changes to the config file require ES to be restarted for it to be applied.