Build Runtime

The Build runtime is the environment Apps are built in.

	Buildpack Builds	Docker Builds
System libraries	Provided by the Stack	User supplied
Network access	Full access through Envoy sidecar	Full access through Envoy sidecar
File system	No storage	No storage
Language runtime	Provided by the Stack	User supplied
User	Specified by the Stack	User supplied
Isolation mechanism	Kubernetes Pod	Kubernetes Pod
DNS	Provided by Kubernetes	Provided by Kubernetes

Environment variables

Environment variables are injected into the Build at runtime. 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 to Builds:

Variable	Purpose
CF_INSTANCE_ADDR	The cluster-visible IP:PORT of the Build.
INSTANCE_GUID	Alias of CF_INSTANCE_GUID .
CF_INSTANCE_IP	The cluster-visible IP of the Build.
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 Build.
LANG	Required by Buildpacks to ensure consistent script load order.
MEMORY_LIMIT	The maximum amount of memory in MB the Build can consume.
VCAP_APPLICATION	A JSON structure containing App metadata.
VCAP_SERVICES	A JSON structure specifying bound services.