The error message "ddl in progress" should plainly state that index builds are in progress.

Rebalancing can fail with the error message "indexer rebalance failure - ddl in progress". This message does not clearly convey that the issue is that 'index builds are in progress'. Further, it would be diagnostically efficient to list which index or indexes are currently building. For example, "indexer rebalance failure - index X, Y, Z currently in 'Building' status".