The issue aims to solve the problem of redeploying HBase clusters on cloud.
I can not find the issue but IIRC, the AWS guys said they tried to do the following steps while redeploying a customer's HBase cluster: 1. Disable write to cluster, flush all data to disk(which is actually S3) 2. Recreate the cluster with a set of new machines, and also a new zk and a new HDFS(for writing WAL) Then the new cluster just hung there and no regions were online. This is because in HMaster startup, we rely on scanning the WAL directory on HDFS to get the previous live region servers, and we will compare the list with the list stored on zookeeper to find out dead region servers and schedule SCPs for them, and then the SCPs will bring the regions online. The problem for the above redeploying operation is, the WAL directory is also cleaned, so we can not get the previous live region servers, so no SCP will be scheduled. This is a bit annoying as we have already flushed all the data out so it should be safe to delete all the WAL data. The idea in HBASE-26245 is to also store a copy of the live region servers in master local region, so when restarting, we could also load the previous live region servers from master local region, instead of only relying on the WAL directory. In this way we could solve the problem of the above redeploying operation. The PR is also ready. https://github.com/apache/hbase/pull/4136 Suggestions and reviews are always welcomed. Thanks.
