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README.adoc

Managing CF App Features with MTA

Table of Contents

This example shows how to use the app-features parameter in an MTA to enable or disable different Cloud Foundry features for your applications. The app-features parameter allows fine-grained control over CF app capabilities during deployment. This feature also helps solve the 130KB environment variable limit issue described in garden-runc-release#160 by providing an alternative way to configure app features without using environment variables.

Official Documentation

For more information about the app-features parameter and other module-specific parameters, see: SAP BTP Documentation - Module-Specific Parameters

Overview

The app-features parameter accepts an array of feature flags that can be used to: - Enable or disable specific Cloud Foundry application features - Control runtime behavior of applications - Customize deployment characteristics per environment

Supported App Features

The following features can be controlled via the app-features parameter:

  • ssh: Enable/disable SSH access to the application container

  • file-based-vcap-services: Use file-based service bindings instead of environment variables

More features may be added in the future as Cloud Foundry evolves, please refer to the following link for the latest updates.

Try it out

Deploy an MTA with App Features

The example demonstrates how to configure different app features using the app-features parameter.

Deploy from directory

This approach uses deployment descriptor mtad.yaml and ready application binaries appBits.zip:

$ cf deploy ./ -f ;

Build and deploy

This approach uses development descriptor mta.yaml and application binaries appBits.zip to build an MTAR archive:

$ mbt build -p cf -t . ;

The built MTAR is then deployed:

$ cf deploy cf.app.features_0.0.0.mtar -f ;
Note
 See mta.yaml or mtad.yaml for details on the app-features parameter configuration.

Examine the result

List the deployed MTA

$ cf mta cf.app.features ;
Showing health and status for multi-target app cf.app.features in org **** / space **** as ****...
OK
Version: 0.0.0
Namespace:

Apps:
name                     requested state   instances   memory   disk   urls
my-featured-app-module   STARTED           1/1         19.6M    5.3M   orgname-spacename-my-featured-app-module.example.com

Services:
name            service   plan          bound apps               last operation
xsuaa-service   xsuaa     application   my-featured-app-module   create succeeded

Verify app features

Check that the app was deployed with the specified features:

$ cf curl v3/apps/$(cf app my-featured-app-module --guid)/features
{
  "resources": [
    {
      "name": "ssh",
      "description": "Enable SSHing into the app.",
      "enabled": true
    },
    {
      "name": "revisions",
      "description": "Enable versioning of an application",
      "enabled": true
    },
    {
      "name": "service-binding-k8s",
      "description": "Enable k8s service bindings for the app",
      "enabled": false
    },
    {
      "name": "file-based-vcap-services",
      "description": "Enable file-based VCAP service bindings for the app",
      "enabled": true
    }
  ],
  "pagination": {
    "total_results": 4,
    "total_pages": 1,
    "first": {
      "href": "/v3/apps/e41aef45-76e1-4c2a-b375-f17b7ae47566/features"
    },
    "last": {
      "href": "/v3/apps/e41aef45-76e1-4c2a-b375-f17b7ae47566/features"
    },
    "next": null,
    "previous": null
  }
}

Test SSH access (if enabled)

If SSH feature is enabled in the app-features:

$ cf ssh my-featured-app ;

Test file based VCAP services (if enabled)

If File based VCAP services is enabled, then service bindings will be set in file with specified path in VCAP_SERVICES_FILE_PATH environment variable:

$ cf env my-featured-app-module
Getting env variables for app my-featured-app-module in org **** / space **** as ****...
System-Provided:
VCAP_SERVICES_FILE_PATH: "/etc/cf-service-bindings/vcap_services"
...

Use Cases

Enable SSH for debugging:

app-features:
  ssh: true

Enable file based VCAP services to mitigate env limit of 130kB:

app-features:
  file-based-vcap-services: true