sticky-node-scheduler is a custom Kubernetes scheduler that schedules all variants of a given pod on the same node.

If a pod variant isn't running on any nodes, we pick a node to schedule on to based on which node is running the least amount of our sticky-scheduled pods. If any varients of a pod are running, then we place all copies of the pod on the same node.

If you're using e.g. EBS volumes, which can only be attached to a single node at a time, and need seamless updates of your stateful Deployments, this might be useful to you.

This scheduler only works with Kubernetes >= 1.6, which support custom schedulers as a beta feature.

NOTE: This is not ready for production usage.

How to use

First, deploy the scheduler into your cluster:

$ kubectl apply -f deployment.yml

Then, for each Deployment or ReplicationController you want to schedule using this scheduler, add:

schedulerName: stickToExistingNodeScheduler

to the pod spec. For instance:

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: my-stateful-service
spec:
  replicas: 2
  template:
    metadata:
      labels:
        app: my-stateful-service
    spec:
      schedulerName: stickToExistingNodeScheduler
      containers:
        - name: my-stateful-service
          image: stateful-service-image

The scheduler identifies 'variants' of your pods based on the metadata.labels entry in your pod template.

Options

The NODE_FILTER_QUERY environment variable controls which nodes are selected for scheduling. By default, it is set to labelSelector=kubernetes.io/role=node, which will filter only nodes (e.g. we won't schedule on to your master nodes).

The POLL_FREQUENCY environment variable controls how often we poll the Kubernetes API for changes, per second. The default is 0.5.

License

Copyright (c) 2016, 2017 Shotwell Labs, Inc.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.