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Scheduler-Worker Cluster Architecture

Read full blog post here: http://www.koraygocmen.com/blog/single-scheduler-multiple-worker-architecture-with-grpc-and-go-part-1

Goal

  • Build a scheduler and worker architecture that supports HTTP requests on the scheduler and translates them to GRPC requests on workers.
  • Any application outside of the GRPC cluster can make HTTP requests to trigger jobs on the cluster and can also create distributed jobs as well.

General Overview

  • Support single scheduler and multiple workers.
  • The scheduler must be aware of all workers' states. (requires the workers to register and deregister when going offline)
  • The scheduler and the workers authenticate with each other via SSL.
  • The scheduler and workers, both need to have GRPC-APIs.
    • The scheduler GRPC-API support:
      • Register a worker
      • Deregister a worker
    • The worker GRPC-API support:
      • Start a job
      • Stop a job
      • Return the status of a job
      • Return a stream of output for a running job.
  • The scheduler also has an HTTP-API (which will be translated and proxied to GRPC requests):
    • Start a job on a specific worker (with worker ID, command and path to the job)
    • Stop a job on a specific worker (with worker ID and job ID)
    • Query a job on a specific worker (with worker ID and job ID)
    • Return the output stream of a job a specific worker (with worker ID and job ID)

Scheduler Overview

  • Scheduler Details
  • API Docs
  • All config parameters are specified in the config.toml file
  • Support a GRPC-API (Appendix A) and an HTTP-API.
  • When a worker registers, a UUID is assigned to the worker and worker details are kept in a map.
  • HTTP requests are translated into GRPC requests on the specified server.
  • Starting a job on a specific worker
    • Request: 
      {
  "worker_id": "71382ed1-471d-4ae3-b572-f67d178f04e9",
  "path": "worker/scripts/count.sh",
  "command": "bash"
}
    • Response: 
      {
  "job_id": "6c26a00e-3017-11e9-b210-d663bd873d93"
}

Worker Overview

  • Worker Details
  • All config parameters are specified in the config.toml file
  • Support a GRPC-API (Appendix B)
  • Jobs are basically scripts that are held in the specified folder in the config.
  • When a job is started by the scheduler, a job object is created by the worker
    • This object specifies where the output of the job will be piped.
    • Also holds which command and which path was requested.

TODO:

  • Finish streaming output of a job
  • Change the insecure dialing for grpc