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1. If "-Dsolr.node.roles" parameter is not passed, it is implicitly assumed to be "-Dsolr.nodes.role=data" (due to backcompat reasons and also so that those who don't use the role feature don't need any extra parameters).
   
2. Roles are static and immutable for the entire life cycle of a node. Once a node starts up with a role, it registers the role in ZK and that sticks around until the node is stopped/restarted.
   
3. The bar for adding new roles in future should be high so it is not abused as any other tag or label for any tiny feature. It should be reserved for functionality that may benefit from a dedicated set of nodes.

Public Interfaces

There will just one supported way to use the roles functionality:

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