scheduler.sh

#!/usr/bin/env bash
#
# A kubernetes scheduler written in bash
# dependencies: kubectl, curl
# Runs against localhost:8001 by default
# Use `kubectl proxy` to proxy to master without https
#
# Author: Justin Garrison
# justingarrison.com
# @rothgar

set -eo pipefail
# uncomment to see all commands in stdout
# set -x

SERVER="${SERVER:-localhost:8001}"
SCHEDULER="${SCHEDULER:-bashScheduler}"

while true; do
  # Get a list of all our pods in pending state
  for POD in $(kubectl --server ${SERVER} get pods \
              --output jsonpath='{.items..metadata.name}' \
              --all-namespaces \
              --field-selector=status.phase==Pending); do

    SCHEDULER_NAME=$(kubectl get pod ${POD} \
                    --output jsonpath='{.spec.schedulerName}')

    if [ "${SCHEDULER_NAME}" == "${SCHEDULER}" ]; then
      # Get the pod namespace
      NAMESPACE=$(kubectl get pod ${POD} \
                  --output jsonpath='{.metadata.namespace}')

      # Get an array for all of the nodes
      # We could optionally check if the nodes are ready
      NODES=($(kubectl --server ${SERVER} get nodes \
              --output jsonpath='{.items..metadata.name}'))

      # Store a number for the length of our NODES array
      NODES_LENGTH=${#NODES[@]}

      # Randomly select a node from the array
      # $RANDOM % $NODES_LENGTH will be the remainder
      # of a random number divided by the length of our nodes
      # In the case of 1 node this is always ${NODES[0]}
      NODE=${NODES[$[$RANDOM % $NODES_LENGTH]]}

      # Bind the current pod to the node selected
      curl --silent --fail \
        --header "Content-Type:application/json" \
        --request POST \
        --data '{"apiVersion":"v1",
                "kind": "Binding", 
                "metadata": {
                  "name": "'${POD}'"
                  }, 
                "target": {
                  "apiVersion": "v1", 
                  "kind": "Node", 
                  "name": "'${NODE}'"
                  }
                }' \
        http://${SERVER}/api/v1/namespaces/${NAMESPACE}/pods/${POD}/binding/ >/dev/null \
        && echo "Assigned ${POD} to ${NODE}" \
        || echo "Failed to assign ${POD} to ${NODE}"
    fi
  done
  echo "Nothing to do...sleeping."
  sleep 6s
done