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Configuring an Application

A Deis application stores config in environment variables.

Setting Environment Variables

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 Health Checks

By default, Workflow only checks that the application starts in their Container. If it is preferred to have Kubernetes respond to application health, a health check may be added by configuring a health check probe for the application.

The health checks are implemented as Kubernetes container probes. A liveness and a readiness probe can be configured, and each probe can be of type httpGet, exec, or tcpSocket depending on the type of probe the container requires.

A liveness probe is useful for applications running for long periods of time, eventually transitioning to broken states and cannot recover except by restarting them.

Other times, a readiness probe is useful when the container is only temporarily unable to serve, and will recover on its own. In this case, if a container fails its readiness probe, the container will not be shut down, but rather the container will stop receiving incoming requests.

httpGet probes are just as it sounds: it performs a HTTP GET operation on the Container. A response code inside the 200-399 range is considered a pass.

exec probes run a command inside the Container to determine its health, such as cat /var/run/myapp.pid or a script that determines when the application is ready. An exit code of zero is considered a pass, while a non-zero status code is considered a fail.

tcpSocket probes attempt to open a socket in the Container. The Container is only considered healthy if the check can establish a connection. tcpSocket probes accept a port number to perform the socket connection on the Container.

Health checks can be configured on a per-application basis using deis healthchecks:set. To configure a httpGet liveness probe:

$ deis healthchecks:set liveness httpGet 80
=== peachy-waxworks Healthchecks
Liveness
--------
Initial Delay (seconds): 50
Timeout (seconds): 50
Period (seconds): 10
Success Threshold: 1
Failure Threshold: 3
Exec Probe: N/A
HTTP GET Probe: Path="/" Port=80 HTTPHeaders=[]
TCP Socket Probe: N/A

Readiness
---------
No readiness probe configured.

If the application relies on certain headers being set (such as the Host header) or a specific URL path relative to the root, you can also send specific HTTP headers:

$ deis healthchecks:set liveness httpGet 80 \
    --path /welcome/index.html \
    --header "X-Client-Version=v1.0"
=== peachy-waxworks Healthchecks
Liveness
--------
Initial Delay (seconds): 50
Timeout (seconds): 50
Period (seconds): 10
Success Threshold: 1
Failure Threshold: 3
Exec Probe: N/A
HTTP GET Probe: Path="/welcome/index.html" Port=80 HTTPHeaders=[X-Client-Version=v1.0]
TCP Socket Probe: N/A

Readiness
---------
No readiness probe configured.

To configure an exec readiness probe:

$ deis healthchecks:set readiness exec -- /bin/echo -n hello
=== peachy-waxworks Healthchecks
Liveness
--------
No liveness probe configured.

Readiness
---------
Initial Delay (seconds): 50
Timeout (seconds): 50
Period (seconds): 10
Success Threshold: 1
Failure Threshold: 3
Exec Probe: Command=[/bin/echo -n hello]
HTTP GET Probe: N/A
TCP Socket Probe: N/A

You can overwrite a probe by running deis healthchecks:set again:

$ deis healthchecks:set readiness httpGet 80
=== peachy-waxworks Healthchecks
Liveness
--------
No liveness probe configured.

Readiness
---------
Initial Delay (seconds): 50
Timeout (seconds): 50
Period (seconds): 10
Success Threshold: 1
Failure Threshold: 3
Exec Probe: N/A
HTTP GET Probe: Path="/" Port=80 HTTPHeaders=[]
TCP Socket Probe: N/A

Configured health checks also modify the default application deploy behavior. When starting a new Pod, Workflow will wait for the health check to pass before moving onto the next Pod.