Usage of nstar package on VMware Tanzu Platform for Cloud Foundry

Products

• VMware Tanzu Application Service

Issue/Introduction

This KB aims to explain the usage of the nstar package in Diego cell and Isolation segments on VMware Tanzu Platform for Cloud Foundry (TAS)

Environment

TAS diego cell and Isolation segment

Resolution

This package is used to cache artifacts on diego-cell VMs. and resides at the following path: /var/vcap/data/packages/guardian/<uuid>/bin/nstar. The acronym "nstar" refers to "namespaced tar".

Garden component utilizes nstar to manage the streaming of application staging or running artifacts, such as application droplets or buildpacks, into or from containers onto host filesystem.  

Garden is shipped with the specific version of tar package that it is compatible with. The tar package gets compiled on the stemcell VM. Because it is streaming from or to the host VM it needs to run tar on the host OS to have correct permissions rather than within the container's filesystem. nstar invokes tar on the host to set correct permissions inside of the container for all artifact files.