# Deploying an Application

An [Application][] is deployed to Deis using `git push` or the `deis` client.

## Supported Applications

Deis Workflow can deploy any application or service that can run inside a Docker container.  In order to be scaled
horizontally, applications must follow the [Twelve-Factor App][] methodology and store any application state in external
backing services.

For example, if your application persists state to the local filesystem -- common with content management systems like
Wordpress and Drupal -- it cannot be scaled horizontally using `deis scale`.

Fortunately, most modern applications feature a stateless application tier that can scale horizontally inside Deis.

## Login to the Controller

!!! important
	if you haven't yet, now is a good time to [install the client][install client] and [register](../users/registration.md).

Before deploying an application, users must first authenticate against the Deis [Controller][]
using the URL supplied by their Deis administrator.

```
$ deis login http://deis.example.com
username: deis
password:
Logged in as deis
```

## Select a Build Process

Deis Workflow supports three different ways of building applications:

### Buildpacks

Heroku buildpacks are useful if you want to follow Heroku's best practices for building applications or if you are porting an application from Heroku.

Learn how to deploy applications [using Buildpacks](../applications/using-buildpacks.md).


### Dockerfiles

Dockerfiles are a powerful way to define a portable execution environment built on a base OS of your choosing.

Learn how to deploy applications [using Dockerfiles](../applications/using-dockerfiles.md).


### Docker Image

Deploying a Docker image onto Deis allows you to take a Docker image from either a public
or a private registry and copy it over bit-for-bit, ensuring that you are running the same
image in development or in your CI pipeline as you are in production.

Learn how to deploy applications [using Docker images](../applications/using-docker-images.md).

## Tuning Application Settings

It is possible to configure a few of the [globally tunable](../applications/managing-app-configuration.md) settings on per application basis using `config:set`.

Setting                                         | Description
----------------------------------------------- | ---------------------------------
DEIS_DEPLOY_BATCHES                             | the number of pods to bring up and take down sequentially during a scale (default: number of available nodes)
DEIS_KUBERNETES_DEPLOYMENTS                     | if enabled [Deployments][] is used to handle an application deploy instead of [ReplicationControllers][]
                                                | any value is acceptable to turn on [Deployments][], to turn it off either remove or pass an empty string (default: off)
KUBERNETES_DEPLOYMENTS_REVISION_HISTORY_LIMIT   | how many [revisions][[kubernetes-deployment-revision]] Kubernetes keeps around of a given Deployment (default: all revisions)

When `DEIS_KUBERNETES_DEPLOYMENTS=1` is set on an application then Deis Workflow will use [Deployments][] internally instead of [ReplicationControllers][].

The advantage of that is that rolling-updates will happen server-side in Kubernetes instead of in Deis Workflow Controller,
along with a few other Pod management related functionality. This allows a deploy to continue even when the CLI connection is interrupted.

Deis Workflow will behave the same way with `DEIS_KUBERNETES_DEPLOYMENTS` enabled or disabled. The changes are behind the scenes.
Where you will see differences while using the CLI is `deis ps:list` will output Pod names differently.

Behind the scenes your application deploy will be built up of a Deployment object per process type,
each having multiple ReplicaSets (one per release) which in turn manage the Pods running your application.

[install client]: ../users/cli.md#installation
[application]: ../reference-guide/terms.md#application
[controller]: ../understanding-workflow/components.md#controller
[Twelve-Factor App]: http://12factor.net/
[Deployments]: http://kubernetes.io/docs/user-guide/deployments/
[kubernetes-deployment-revision]: http://kubernetes.io/docs/user-guide/deployments/#revision-history-limit
[ReplicationControllers]: http://kubernetes.io/docs/user-guide/replication-controller/