kohend / dcos-commons

Simplifying stateful services

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DC/OS SDK is a collection of tools, libraries, and documentation for easy integration of technologies such as Kafka, Cassandra, HDFS, Spark, and TensorFlow with DC/OS.

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Understanding the Hello World Service Specification

The service specification declaratively defines the helloworld service:

name: "helloworld"
pods:
  helloworld:
    count: {{COUNT}}
    tasks:
      server:
        goal: RUNNING
        cmd: "echo 'Hello World!' >> helloworld-container-volume/output && sleep 10"
        cpus: {{SERVER_CPU}}
        memory: 32
        volume:
          path: "helloworld-container-volume"
          type: ROOT
          size: 64

In the above YAML file, we have:

• Defined a service with the name helloworld
• Defined a pod specification for our helloworld pod using:

pods:
  helloworld:
    count: {{COUNT}}
    tasks:
      ...

• Declared that we need atleast {{COUNT}} instances of the helloworld pod running at all times, where COUNT is the environment variable that is injected into the scheduler process at launch time via Marathon. It defaults to 1 for this example.
• Defined a task specification for our server task using:

tasks:
  server:
    goal: RUNNING
    cmd: "echo 'Hello World!' >> helloworld-container-volume/output && sleep 10"
    cpus: {{SERVER_CPU}}
    memory: 32

We have configured it to use {{SERVER_CPU}} CPUs (which defaults to 0.5 for this example) and 32 MB of memory.

• And finally, configured a 64 MB persistent volume for our server task where the task data can be persisted using:

volume:
  path: "helloworld-container-volume"
  type: ROOT
  size: 64

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References

• Developer Guide
• Javadocs

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Contributions

Contributions are welcome! See CONTRIBUTING.

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License

DC/OS SDK is licensed under the Apache License, Version 2.0.