We've even used cursors to migrate implementations; in our case, we were migrating from solr5 to solr7. When you started a session, you were allocated to solr5

We've even used cursors to migrate implementations; in our case, we were migrating from solr5 to solr7. When you started a session, you were allocated to solr5 or solr7 according to the business rules in effect; the solr7 cursors were prefixed with solr7-, so that in subsequent requests we could send you to the same major version. It could work the same way with load balancing too I guess.