App runtime

The app runtime is the environment apps are executed in.

	Buildpack Apps	Container Image Apps
System libraries	Provided by the Stack	Provided in the container
Network access	Full access through Envoy sidecar	Full access through Envoy sidecar
File system	Ephemeral storage	Ephemeral storage
Language runtime	Supplied by the Stack or Buildpack	Built into the container
User	Specified by the Stack	Specified on the container
Isolation mechanism	Kubernetes Pod	Kubernetes Pod
DNS	Provided by Kubernetes	Provided by Kubernetes

Environment variables

Environment variables are injected into the app at runtime by Kubernetes. Variables are added based on the following order, where later values override earlier ones with the same name:

1. Space (set by administrators)
2. App (set by developers)
3. System (set by Kf)

Kf provides the following system environment variables:

Variable	Purpose
CF_INSTANCE_ADDR	The cluster-visible IP:PORT of the App instance.
CF_INSTANCE_GUID	The UUID of the App instance.
INSTANCE_GUID	Alias of CF_INSTANCE_GUID.
CF_INSTANCE_INDEX	The index number of the App instance, this will ALWAYS be 0.
INSTANCE_INDEX	Alias of CF_INSTANCE_INDEX.
CF_INSTANCE_IP	The cluster-visible IP of the App instance.
CF_INSTANCE_INTERNAL_IP	Alias of CF_INSTANCE_IP
VCAP_APP_HOST	Alias of CF_INSTANCE_IP
CF_INSTANCE_PORT	The cluster-visible port of the App instance. In Kf this is the same as PORT.
DATABASE_URL	The first URI found in a VCAP_SERVICES credential.
LANG	Required by Buildpacks to ensure consistent script load order.
MEMORY_LIMIT	The maximum amount of memory in MB the App can consume.
PORT	The port the App should listen on for requests.
VCAP_APP_PORT	Alias of PORT.
VCAP_APPLICATION	A JSON structure containing App metadata.
VCAP_SERVICES	A JSON structure specifying bound services.

Service credentials from bound services get injected into Apps via the VCAP_SERVICES environment variable. The variable is a valid JSON object with the following structure.

VCAPServices

A JSON object where the keys are Service labels and the values are an array of VCAPService. The array represents every bound service with that label. User provided services are placed under the label user-provided.

Example

{
  "mysql": [...],
  "postgresql": [...],
  "user-provided": [...]
}

VCAPService

This type represents a single bound service instance.

Example

{
  "binding_name": string,
  "instance_name": string,
  "name": string,
  "label": string,
  "tags": string[],
  "plan": string,
  "credentials": object
}

Fields

Field	Type	Description
binding_name	string	The name assigned to the service binding by the user.
instance_name	string	The name assigned to the service instance by the user.
name	string	The binding_name if it exists; otherwise the instance_name.
label	string	The name of the service offering.
tags	string[]	An array of strings an app can use to identify a service instance.
plan	string[]	The service plan selected when the service instance was created.
credentials	object	The service-specific credentials needed to access the service instance.

Note: Use the tags field to discover services in your App rather than filtering by plan/label so you can swap implementations and providers per environment.

Note: The credentials field is often an object with string keys and values. However, the values are allowed to be any type.

VCAP_APPLICATION

TheVCAP_APPLICATION environment variable is a JSON object containing metadata about the App.

Example

{
  "application_id": "12345",
  "application_name": "my-app",
  "application_uris": ["my-app.example.com"],
  "limits": {
    "disk": 1024,
    "mem": 256
  },
  "name": "my-app",
  "process_id": "12345",
  "process_type": "web",
  "space_name": "my-ns",
  "uris": ["my-app.example.com"]
}

Fields

Field	Type	Description
application_id	string	The GUID identifying the App.
application_name	string	The name assigned to the App when it was pushed.
application_uris	string[]	The URIs assigned to the App.
limits	object	The limits to disk space, and memory permitted to the App. Memory and disk space limits are supplied when the App is deployed, either on the command line or in the App manifest. Disk and memory limits are represented as integers, with an assumed unit of MB.
name	string	Identical to application_name.
process_id	string	The UID identifying the process. Only present in running App containers.
process_type	string	The type of process. Only present in running App containers.
space_name	string	The human-readable name of the Space where the App is deployed.
uris	string[]	Identical to application_uris.

Missing Fields

Some fields in VCAP_APPLICATION that are in Cloud Foundry are currently not supported in Kf.

Besides CF-specific and deprecated fields (cf_api, host, users) the fields that are not supported in Kf are:

• application_version (identical to version)
• organization_id
• organization_name
• space_id
• start (identical to started_at)
• started_at_timestamp (identical to state_timestamp)