Distributed!

Was That All Folks?

Late in 2014, Mesosphere announced the Datacenter Operating System (DCOS) [18]. Mesophere describes DCOS as a "new kind of operating system that spans all of the servers in a physical or cloud-based data center and runs on top of any Linux distribution." Mesos assumes the system kernel role at the base of the DCOS system.

The Marathon [19] and Chronos [20] frameworks will also be part of the package. Marathon manages jobs with a longer execution time. If you compare DCOS with a classical Unix-style operating system, Marathon is equivalent to the init process. You can also view Marathon as a meta-scheduler. Marathon starts the other frameworks and monitors them. In doing so, Marathon checks whether the desired number of job instances are running. If a slave fails, Marathon starts the failed processes on the remaining Mesos nodes.

Chronos, which runs jobs in line with a defined schedule, is the equivalent of cron. In DCOS, Chronos is the first framework started by Marathon. Both have a REST interface for interaction.

Figure 3 shows a highly simplified DIY version of DCOS. Marathon (Figure 4) and Chronos are registered as Mesos applications. The jobs are simple sleep commands. The use of ZooKeeper is mandatory for DCOS. Both Marathon and Chronos require ZooKeeper.

Figure 3: A narrow-gauge version of the Datacenter Operating System: Mesos with Marathon and Chronos.

Figure 4: Marathon starts and manages other frameworks.

When this issue went to press, the DCOS by Mesosphere was still in beta. You can visit the Mesosphere website [18] to download a pre-release version.

Conclusions of a Kind

Just a glance at the list of enterprises that have been using Mesos for years is more than enough to show that Mesos is an exciting project. The number of frameworks based on Mesos is also quite impressive. Mesos really comes into its own in large and heterogeneous IT landscapes. The Mesos framework offers a simple approach to pooling existing compute capacities and providing them either as a bulk package or bit by bit. This form of abstraction is also very attractive for smaller IT environments.