...

• Use autoscaling to stop data (replicas) from being placed on nodes. But, that framework itself has been re-written from Solr 8x to 9x, hence we don’t have a recommendation for users for a consistent way to achieve this. Also, 9x autoscaling framework doesn't support placement plugin chaining, and hence placement plugins shouldn't be used for a first class support of node roles.
  
• OVERSEER role is already available today, it indicates "preferred" overseer.

Discussions (summary)

• No negative roles

There shouldn’t be a concept of “not data” or “not overseer” etc.

Everyone agree

• Roles on/off by default?

Jason, Ilan, Houston, Jan: All roles should be on by default. Having all roles on by default is less complicated for users, instead of “treating data role differently from other roles”.

Ishan, Noble, ?Gus?: Only those roles to be on by default that are needed for backcompat, so that we don’t take premature decision for any future roles introduced later. When a new role is introduced, whether that new role should be enabled by default or not can be decided then.

• Which branch to target?

Jan, Ishan, Noble: New feature to be added to 9x branch

• Need for roles?

Tim, Ilan: new concept of nodes unnecessary since everything that's proposed can be achieved using changes to new autoscaling framework and replica placement plugins. “This proposal in its current form (data and overseer roles) doesn't offer much that can't be reasonably achieved by other means” -- Ilan

Ishan, Noble: A first class concept of roles is important so that this functionality is expected to work, irrespective of whatever custom placement plugins users deploy (since placement plugins don't support chaining).

• Roles for collections?

Ilan: Role aware collections. “If we make collections role-aware for example (replicas of that collection can only be placed on nodes with a specific role, in addition to the other role based constraints), the set of roles should be user extensible and not fixed.”

Ishan: Role aware collections can be implemented separately later using node roles and placement plugins. As for user extensible roles, a separate concept of user defined node labels (as a separate feature) make more sense. This SIP is more about first class roles (that comes pre-defined with Solr).

• Configuration

Sysprops vs solr.xml+sysprops vs envvars:

Shawn: Solr.xml and/or envvars

Houston,Ilan: Sysprops and/or envvars

Ishan,Noble: Sysprops

Jan: SIP-11