Repository: rothgar/bashScheduler
Branch: main
Commit: f676d8048578
Files: 3
Total size: 4.1 KB

Directory structure:
gitextract_mu2czho1/

├── README.md
├── nginx.deploy.yaml
└── scheduler.sh

================================================
FILE CONTENTS
================================================

================================================
FILE: README.md
================================================
![](img/banner.png)

Kubernetes bash scheduler
============

### This is a really bad idea

I made it because it was helpful for me to learn :bowtie:
I hope you learn something too.

## How to run it 

Please don't ever use this on a production kubernetes cluster!!!

Run it against a local [kind](https://kind.sigs.k8s.io/) cluster.

```
kind create cluster
```

Create pods that use the custom scheduler.

```
kubectl apply -f https://raw.githubusercontent.com/rothgar/bashScheduler/main/nginx.deploy.yaml
```

You should see nginx pods with Pending status

```
NAME                     READY   STATUS    RESTARTS   AGE
nginx-56dcc974bc-8ss4m   0/1     Pending   0          49m                                              
nginx-56dcc974bc-94ltw   0/1     Pending   0          49m                                              
nginx-56dcc974bc-tnz6s   0/1     Pending   0          49m 
```

Then proxy your localhost to the kubernetes api server

```
kubectl proxy
Starting to serve on 127.0.0.1:8001
```

Now in a new terminal run

```
curl -sL https://raw.githubusercontent.com/rothgar/bashScheduler/main/scheduler.sh | bash
```

You should see similar output to
```
Assigned nginx-56dcc974bc-8ss4m to kind-control-plane
Assigned nginx-56dcc974bc-94ltw to kind-control-plane
Assigned nginx-56dcc974bc-tnz6s to kind-control-plane
```

Look at the code and see what it's doing.
Uncomment `set -x` to see all the commands run.

Have fun :shipit:


================================================
FILE: nginx.deploy.yaml
================================================
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      schedulerName: bashScheduler
      containers:
      - name: nginx
        image: nginx
        resources:
          limits:
            memory: "128Mi"
            cpu: "500m"
        ports:
        - containerPort: 80

================================================
FILE: 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