Hi All, I'd like to mention some changes that have been discussed amongst the committers but have not yet been shared broadly with the list.
The central component of Mesos is the "Master". The Master is responsible for administering slaves, frameworks, and resource offers. It also handles task launching requests, status updates, and framework messages. As you may or may not know, the Master is currently stateless, in that it does not persist any information across failovers. Rather, the Master currently recovers all of its state from the slaves and frameworks that re-register after a failover. This design has many benefits. First, failing over a Master is a trivial operation. Second, we do not have the performance overhead and complexity of dealing with persistent state. However, this design opens up a few cases for information loss in the system. For example, when no Master is running and a Slave fails permanently, there's no knowledge of this in the failed over Master. In order to detect these events, we'd like to add persistence of the registered slaves. The first step for this was creating the Registrar: https://reviews.apache.org/r/14383/ https://reviews.apache.org/r/14384/ https://reviews.apache.org/r/15099/ https://reviews.apache.org/r/15100/ The Registrar is responsible for keeping the official records of the master. This will initially include SlaveInfo in order to correctly handle cases like the example I provided above. The Registrar is agnostic to the underlying data storage and can be backed by a local LevelDB, by ZooKeeper (for high availability Masters), and in the future by our reconfigurable replicated log. The next steps are to implement "statefulness" in the Master using the Registrar. So far I've sent out some of the preliminary cleanup work, and I have a few pending patches that I'm in the process of cleaning up that implement this fully so keep an eye out for those. In the longer term, we will add persistence of framework information in the same vein. That is, handling framework failures in the presence of Master failures. Cheers! Ben
