soundcloud/roshi — pull request #20 by peterbourgon (2014-07-09 11:34:48+00:00)
Title: Differentiate read- and write-clusters

The ability to place a cluster into "write-only mode" is intended to facilitate operational maneuvers, like re-provisioning a farm. The intended workflow is:

- Add a new cluster, in write-only mode
- Perform a backfill, to populate the new cluster
- Perform sanity checks, e.g. equal key counts
- Switch the cluster to normal read+write mode

The new mode prevents farm read strategies from querying what's effectively a known-bad set of instances while they're spinning up.