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title:Configure an Application on Deis
description:Instructions for developers using Deis to configure applications.

Configure an Application

A Deis application stores config in environment variables.

Configure the Application

Use deis config to modify environment variables for a deployed application.

$ deis help config
Valid commands for config:

config:list        list environment variables for an app
config:set         set environment variables for an app
config:unset       unset environment variables for an app
config:pull        extract environment variables to .env
config:push        set environment variables from .env

Use `deis help [command]` to learn more.

When config is changed, a new release is created and deployed automatically.

You can set multiple environment variables with one deis config:set command, or with deis config:push and a local .env file.

$ deis config:set FOO=1 BAR=baz && deis config:pull
$ cat .env
FOO=1
BAR=baz
$ echo "TIDE=high" >> .env
$ deis config:push
Creating config... done, v4

=== yuppie-earthman
DEIS_APP: yuppie-earthman
FOO: 1
BAR: baz
TIDE: high

Attach to Backing Services

Deis treats backing services like databases, caches and queues as attached resources. Attachments are performed using environment variables.

For example, use deis config to set a DATABASE_URL that attaches the application to an external PostgreSQL database.

$ deis config:set DATABASE_URL=postgres://user:pass@example.com:5432/db
=== peachy-waxworks
DATABASE_URL: postgres://user:pass@example.com:5432/db

Detachments can be performed with deis config:unset.

Custom Domains

You can use deis domains to add or remove custom domains to your application:

$ deis domains:add hello.bacongobbler.com
Adding hello.bacongobbler.com to finest-woodshed... done

Once that's done, you can go into your DNS registrar and set up a CNAME from the new appname to the old one:

$ dig hello.deisapp.com
[...]
;; ANSWER SECTION:
hello.bacongobbler.com.         1759    IN    CNAME    finest-woodshed.deisapp.com.
finest-woodshed.deisapp.com.    270     IN    A        172.17.8.100

Note

Setting a CNAME for your root domain can cause issues. Setting your @ record to be a CNAME causes all traffic to go to the other domain, including mail and the SOA ("start-of-authority") records. It is highly recommended that you bind a subdomain to an application, however you can work around this by pointing the @ record to the address of the load balancer (if any).

Custom Health Checks

By default, Deis checks if the container is running for health checks. You can change both the healthcheck URL and the expected status code by setting custom config:

$ deis config:set HEALTHCHECK_URL=/404.html
=== peachy-waxworks
HEALTHCHECK_URL: /404.html
$ deis config:set HEALTHCHECK_STATUS_CODE=404
=== peachy-waxworks
HEALTHCHECK_STATUS_CODE: 404
HEALTHCHECK_URL: /404.html

If a new release does not pass the healthcheck, the application will be rolled back to the previous release. Beyond that, if an application container responds to a heartbeat check with a different status than is expected, the :ref:`router` will mark that container as down and stop sending requests to that container.

Track Changes

Each time a build or config change is made to your application, a new :ref:`release` is created. Track changes to your application using deis releases.

$ deis releases
=== peachy-waxworks Releases
v4      3 minutes ago                     gabrtv deployed d3ccc05
v3      1 hour 17 minutes ago             gabrtv added DATABASE_URL
v2      6 hours 2 minutes ago             gabrtv deployed 7cb3321
v1      6 hours 2 minutes ago             gabrtv deployed deis/helloworld

Rollback the Application

Use deis rollback to revert to a previous release.

$ deis rollback v2
Rolled back to v2

$ deis releases
=== folksy-offshoot Releases
v5      Just now                          gabrtv rolled back to v2
v4      4 minutes ago                     gabrtv deployed d3ccc05
v3      1 hour 18 minutes ago             gabrtv added DATABASE_URL
v2      6 hours 2 minutes ago             gabrtv deployed 7cb3321
v1      6 hours 3 minutes ago             gabrtv deployed deis/helloworld

Note

All releases (including rollbacks) append to the release ledger.