gist:fff6a45c4ceb6310f81b

title:	Choosing a Scheduler
description:	How to choose a scheduler backend for Deis.

Choosing a Scheduler

The :ref:`scheduler` creates, starts, stops, and destroys each :ref:`container` of your app. For example, a command such as deis scale web=3 tells the scheduler to run three containers from the Docker image for your app.

Deis defaults to using the Fleet Scheduler. A tech preview of the Swarm Scheduler and Mesos with Marathon framework is available for testing. Work is ongoing on Kubernetes-based scheduler with the intent to test those alternatives in future releases of Deis. Keep watching issue 3850

Settings set by scheduler

The following etcd keys are set by the scheduler module of the controller component.

Some keys will exist only if a particular schedulerModule backend is enabled.

Settings used by scheduler

The following etcd keys are used by the scheduler module of the controller component.

setting	description
/deis/controller/schedulerModule	scheduler backend, either "fleet" or "swarm" or mesos_marathon (default: "fleet")

Fleet Scheduler

fleet is a scheduling backend included with CoreOS:

fleet ties together systemd and etcd into a distributed init system. Think of it as an extension of systemd that operates at the cluster level instead of the machine level. This project is very low level and is designed as a foundation for higher order orchestration.

fleetd is already running on the machines provisioned for Deis: no additional configuration is needed. Commands such as deis ps:restart web.1 or deis scale cmd=10 will use fleet by default to manage app containers.

To use the Fleet Scheduler backend explicitly, set the controller's schedulerModule to "fleet":

$ deisctl config controller set schedulerModule=fleet

Swarm Scheduler

Important

The Swarm Scheduler is a technology preview and is not recommended for production use.

swarm is a scheduling backend for Docker:

Docker Swarm is native clustering for Docker. It turns a pool of Docker hosts into a single, virtual host.

Swarm serves the standard Docker API, so any tool which already communicates with a Docker daemon can use Swarm to transparently scale to multiple hosts...

Deis includes an enhanced version of swarm v0.2.0 with node failover and optimized locking on container creation. The Swarm Scheduler uses a soft affinity filter to spread app containers out among available machines.

Swarm requires the Docker Remote API to be available at TCP port 2375. If you are upgrading an earlier installation of Deis, please refer to the CoreOS documentation to enable the remote API.

Note

Known Issues

It is not yet possible to change the default affinity filter.
If swarm can't create all the containers requested during scale, deis rolls back the scale operation.
App containers will not be rescheduled if deis-registry is unavailable.

To test the Swarm Scheduler backend, first install and start the swarm components:

$ deisctl install swarm && deisctl start swarm

Then set the controller's schedulerModule to "swarm":

$ deisctl config controller set schedulerModule=swarm

The Swarm Scheduler is now active. Commands such as deis destroy or deis scale web=9 will use swarm to manage app containers.

To monitor Swarm Scheduler operations, watch the logs of the swarm-manager component, or spy on Docker events directly on the swarm-manager machine:

$ deisctl journal swarm-manager
$ docker -H 172.17.8.102:2395 events
2015-04-30T17:31 172.17.8.100:5000/hungry-variable:v5: (from  node:deis-01) pull
2015-04-30T17:31 172.17.8.100:5000/hungry-variable:v5: (from  node:deis-02) pull
2015-04-30T17:31 02a570: (from 172.17.8.100:5000/hungry-variable:v5 node:deis-01) create
2015-04-30T17:31 02a570: (from 172.17.8.100:5000/hungry-variable:v5 node:deis-01) start
2015-04-30T17:31 61e59c: (from 172.17.8.100:5000/hungry-variable:v5 node:deis-02) create
2015-04-30T17:31 61e59c: (from 172.17.8.100:5000/hungry-variable:v5 node:deis-02) start

Mesos with Marathon framework

Important

The Mesos with Marathon framework Scheduler is a technology preview and is not recommended for production use.

Mesos is a distributed system kernel:

Mesos provides APIs for resource management and scheduling. A framework interacts with Mesos master and schedules and task. A Zookeeper cluster elects Mesos master node. Mesos slaves are installed on each node and they communicate to master with available resources.

Marathon is a Mesos framework for long running applications:

Marathon provides a Paas like feel for long running applications and features like high-availablilty, host constraints, service discovery, load balancing and REST API to control your Apps.

Deis uses Marathon framework to schedule containers. As Marathon is a framework for long running jobs, we are using fleet to run batch processing jobs. deisctl installs standlone Mesos cluster. If you want to install HA mesos cluster please follow aledbf-mesos and set edcd key /deis/scheduler/mesos/marathon to any Marathon node IP address, if the request is received by a non-master Marathon then the request is proxied to master Marathon node.

To test the Marathon Scheduler backend, first install and start the mesos components:

$ deisctl install mesos && deisctl start mesos

Then set the controller's schedulerModule to "mesos_marathon":

$ deisctl config controller set schedulerModule=mesos_marathon

The Marathon framework is now active. Commands such as deis destroy or deis scale web=9 will use Marathon to manage app containers.

Deis starts Marathon on port 8180. You can manage the apps through Marathon UI which is accessible at http://<Marathon-node-IP>:8180