| title: | Choosing a Scheduler |
|---|---|
| description: | How to choose a scheduler backend for Deis. |
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 is available for testing. Work is ongoing on Kubernetes and Mesos-based schedulers with the intent to test those alternatives in future releases of Deis.
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.
| setting | description |
|---|---|
| /deis/scheduler/swarm/host | the swarm manager's host IP address |
| /deis/scheduler/swarm/node | used to identify other nodes in the cluster |
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" (default: "fleet") |
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=fleetImportant
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, Deis returns an error and leaves some containers in the "created" state. Until this behavior is fixed, be mindful of resource limitations on your cluster.
- 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 swarmThen set the controller's schedulerModule to "swarm":
$ deisctl config controller set schedulerModule=swarmThe 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