This presentation talks about different aspects of scheduling in Docker Swarm 1.12

1. Docker 1.12 Swarm
Scheduling
Atharva Chauthaiwale
Juniper Networks.

2. Agenda
 Basic Swarm Scheduling Concepts
 Scheduling criteria
 Resource Awareness
 Labels
 Constraints
 Strategy
 Demo
 WARNING : We are covering docker 1.12 Swarm mode only !!!

3. Swarm Scheduler
Manager
Swarm init
Worker 1
swarm join
Worker 2
swarm join
Worker 3
swarm join
Worker 2
swarm join
docker service create –-name myredis –-replicas 3 redis:latest
Scheduler
kicks in Here !
Main job of scheduler is to decide which node to use when running docker container/service.
docker service update docker service scale

4. Scheduling Criteria
 Resource Availability
 Scheduler is aware of resources available on nodes.
 Labels and Constraints
 Label : attribute of the node
 E.g. environment = test, storage = ssd
 Constraints
 Restrictions applied by Operator while creating a service.
 E.g. docker service create --constraint node.labels.storage==ssd …

5. Engine Labels & Constraints
 Attached to docker Engine
 Adding/Modifying requires Docker engine restart
 https://docs.docker.com/engine/admin/#/configuring-docker
 How to specify Engine labels ( Linux Machine )
 Edit file /etc/default/docker modify DOCKER_OPTS and restart
daemon
 Engine constraints
 docker service create --constraint engine.labels.storage==ssd …

6. Node Labels & Constraints
 Can be added by cluster admin for operational purpose
 Doesn’t require docker engine restart
 docker node update --label-add security=high
 docker node update –label-rm security
 Node constraints
 docker service create --constraint node.labels.deployment.environment
!= test

7. Strategy & Affinity
 Strategy : What happens when two nodes are similar
 Spread strategy : schedule tasks on the least loaded nodes, provided
they meet the constraints and resource requirements.
 Swarm standalone supported Bean pack and Random strategy
NOT SUPPORTED IN SWARM MODE YET !
 Affinity and Anti Affinity
 Affinity: two containers should be together
 Anti Affinity : two containers should not be together
 Supported in swarm standalone

8. Demo
 Setup
 AWS : 3 EC2 instances – Ubuntu 15.10
 1 Manager and 2 workers
Manager
Worker 1
Worker 2
Engine label: com.storage.class=ssd
Engine label: com.storage.class=hdd
Engine label: com.storage.class=hdd

9. References
 Swarm mode scheduler :
https://github.com/docker/swarmkit/blob/master/README.md
 What’s new in Docker 1.12 Scheduling – Docker Captain Ajeet Singh Raina
 Docker1.12 and AWS – Atharva
 Github repo for the demo - https://github.com/achautha/docker-
experiments
Thank you !!