DC/OS can run many different kinds of workloads, which are composed of tasks. DC/OS tasks are Mesos tasks that have been scheduled by either a DC/OS built-in scheduler or a scheduler service running on DC/OS.

Executors

When the scheduler launches a task, it specifies a Mesos Executor, which then executes the task. In Mesos, the scheduler and its executor(s) are called a framework, but within the broader context of DC/OS we often use the terms “scheduler”, “executor”, and “task” explicitly.

Built-in executors

Mesos includes built-in executors that are available to all schedulers, but schedulers can also use their own executors.

• Command Executor - execute shell commands or Docker containers
• Default Executor (Mesos 1.1) - execute a group of shell commands or Docker containers

For more on Mesos executors, see the Mesos Framework Development Guide

Schedulers

Because the task system is so generic, users generally do not create or interact with tasks directly. Instead, schedulers often provide higher level abstractions.

Built-in schedulers

DC/OS has two built-in schedulers:

• The Marathon scheduler provides services (Apps and Pods), which run continuously and in parallel. For more on Marathon services, see the Services docs or the Marathon docs.
• The Metronome scheduler provides jobs, which run immediately or on a defined schedule. For more on Metronome jobs, see the Jobs docs.

User space schedulers

Additional schedulers can be installed as scheduler services on Marathon, either from the Mesosphere Catalog or directly through Marathon.

Example user space schedulers:

• The Kafka scheduler provides Kafka brokers, which run as lifecycle managed Kafka nodes.
• The Cassandra scheduler provides Cassandra nodes, which run as lifecycle managed Cassandra nodes.
• The Spark scheduler (dispatcher) provides Spark jobs, which are themselves schedulers for Spark tasks.

For a full list of installable schedulers (and other packages), see the Mesosphere Catalog package list.