How does Cloud Foundry know an app is working? Health checks. An app health check is a monitoring process that continually checks the state of a running Cloud Foundry app. Cloud Foundry supports three types of health checks:

• http whereby a GET is performed against a web app on its default port - can be used with any app than can provide a HTTP 200 response.
• port whereby a TCP connection is made to one or more ports - can be used where an app can receive TCP connections, including HTTP web apps. This is the default if no health check is specified.
• process whereby the process (PID) running in the container is monitored - useful for apps that don’t support TCP connections e.g. a worker app.

As a developer, you can change health checks for an app. Health checks can be set in the app manifest, or on the command line:

cf set-health-check <APP-NAME> <HEALTH-CHECK-TYPE> --endpoint <CUSTOM-HTTP-ENDPOINT>

---
  ...
  health-check-type: http
  health-check-http-endpoint: /health

Note that the --endpoint flag and health-check-http-endpoint field of the manifest are only applicable when using the http health check type.

After you set the health check configuration of a deployed app with the cf set-health-check command, you must restart the app for the change to take effect.

Let’s update the health check type for the training-app to use a http health check instead of the default port check:

cf set-health-check training-app http

Once the health check method is updated, the app needs to be restarted for the changes to take effect.

cf restart training-app

Ta-da, the training-app is now using a HTTP health check.

You can view the currently-configured health check on an app like so:

cf get-health-check training-app

Note: When we set the health check, we didn’t provide a custom endpoint with the --endpoint flag even though we chose a check of type http. When this flag is omitted, Cloud Foundry defaults to using / as the endpoint. This suffices for a training example, but applications you should provide a dedicated health check endpoint when using a HTTP health check. The endpoint needs to respond within 1 second to be considered healthy by Cloud Foundry, so relying on non-dedicated endpoints serving business logic could compromise the response time and health check results.