coordinator

README

Coordinator Microservice

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📄 Contents

• Contents
  • Description
  • Deployment
  • How does the coordinator work?
  • Directory and File description
  • Common questions

❕ Description

The coordinator's goal is to monitor the kubernetes cluster for newly created pods. Once a pod is created the coordinator will proceeed to to examine the details of the pod and send it to the queue service.

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❕ Deployment of the coodinator service

Before deploying the coordinator.yaml file, please configure the environment variables to the correct values used by the queue microservice.

env:
- name: MQ_HOST
  value: "sched-rabbitmq-0.sched-rabbitmq.custom-scheduler.svc.cluster.local"
- name: MQ_PORT
  value: "5672"
- name: MQ_MANAGE_PORT
  value: "15672"
- name: MQ_USER
  value: "guest"
- name: MQ_PASS
  value: "guest"
- name: DEFAULT_QUEUE
  value: "epsilon.distributed"

The DEFAULT_QUEUE is the queue used by the general-purpose scheduler. In Epsilon, atleast one scheduler service need to act as the default scheduler.

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❕ Coordinator algorithm

[STEP 1]
The coordinator monitors for the creation of a new pod.

[STEP 2]
When a new pod is created the coodinator will check the SchedulerName field of the pod configuration to ensure that the pod is configured to be scheduled by the Epsilon scheduler.

The function that checks for the scheduler name can be found in main.go at line 193-195

[STEP 3]
Once a pod passes the check in STEP 2. The coordinator will put the pod in a FIFO queue till the handler processes it.

[STEP 4]
The coordinator handler will fetch the pod from the queue and check if a specific shceduler queue is specified inside the pod configuration. If there isn't a scheduler queue specified in the pod labels the coordinator will send the pod to the default scheduler queue.

The handle.go file contains the pod handling algorithm and all the coodinator handler functions. The function that fetches a pod from the queue and processes it is called ObjectSync(). (Line 88-92 of handler.go)

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❕ Directory and File Description

Directory Name	File name	Description
/	main.go	Implementation code of the main routine
/	controller.go	Implementation code containing a queue implementation for buffering pods that are created and waiting to be scheduled
/	handler.go	Contains the implementation coordinator logic and how it select which scheduler to send the pod to
/helper	helper.go	Contain helper methods use by the main routine
/docker	Dockerfile	Used by docker to create a docker image
/yaml	coordinator.yaml	Deployment file to deploy the scheduler in a Kubernetes cluster

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❕ Common questions

How to change the SchedulerName used by Epsilon to something else?

The SchedulerName can be changed by changing the name to check in the if statement in main.go at line 193.

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