Use the swift-ring-builder utility to build and manage rings. This utility assigns partitions to devices and writes an optimized Python structure to a gzipped, serialized file on disk for transmission to the servers. The server processes occasionally check the modification time of the file and reload in-memory copies of the ring structure as needed. If you use a slightly older version of the ring, one of the three replicas for a partition subset will be incorrect because of the way the ring-builder manages changes to the ring. You can work around this issue.
The ring-builder also keeps its own builder file with the ring information and additional data required to build future rings. It is very important to keep multiple backup copies of these builder files. One option is to copy the builder files out to every server while copying the ring files themselves. Another is to upload the builder files into the cluster itself. If you lose the builder file, you have to create a new ring from scratch. Nearly all partitions would be assigned to different devices and, therefore, nearly all of the stored data would have to be replicated to new locations. So, recovery from a builder file loss is possible, but data would be unreachable for an extended time.
