Affects Version/s: None
Fix Version/s: None
Currently Hadoop uses local files to determine cluster membership. With HDFS for example, dfs.hosts and dfs.hosts.exclude are used.
To enable tighter integrations cluster membership should be an interface, with the current file-based functionality provided as the default implementation. The common case would be no functional change, however, sites could plug an alternative implementation in, such as pulling the machine lists from a machine database.
Two machine lists, includes and excludes, are used to define cluster membership and state. HostsFileReader currently handles reading these lists from files, who's names are passed in by FSNamesystem for HDFS and JobTracker for MR.
The proposed change is adding a HostsReader interface to common, and changing HostsFileReader to an abstract class that functions the same as today.
Two new classes, DFSHostsFileReader and MRHostsFileReader, extend HostsFileReader and simply pass the appropriate file names in. These new classes are needed because config key names live outside common.
Two new conf keys, defaulting to the file-based readers, would be added to choose a different hosts reader: dfs.namenode.hosts.reader.class mapreduce.jobtracker.hosts.reader.class
Comments/suggestions? I have most of this written already but would love some feedback on the general idea before posting the diff.