Using Windows Stemcells

Overview

A stemcell is a customized operating system image containing the filesystem for BOSH-managed virtual machines. When deployed, it includes a process, the BOSH Agent, which is pre-configured to communicate with the orchestrating VM, the BOSH Director. The BOSH Agent is responsible for executing and monitoring jobs on the VM.

PAS for Windows 2012R2 deployments currently use a stemcell based on Windows Server 2012 R2.

Root Disk Sizing

The size of the stemcell’s root disk determines the minimum root disk size of any Windows VM that the BOSH Director can create from that stemcell. The relationship between a stemcell’s disk size and the root disk size of the Windows cells depends on your IaaS as shown in the table below.

IaaS Stemcell root disk size Possible root disk sizes for Windows cells
Azure 127 GB 127 GB
AWS 30 GB 30 GB or larger (for stemcell 1200.9 and later)
GCP 50 GB 50 GB or larger
vSphere Recommended 128 GB+* Same as stemcell minimum root disk size

*Because you create your own stemcell on vSphere, you can control its root disk size. See Creating a vSphere Stemcell Manually for more information.

In the PAS for Windows 2012R2 tile > Resource Config pane, the VM types that you can choose from reflect the disk size constraints in the table above.

Light Stemcells

Light stemcells are metadata files that enable you to deploy VMs without uploading the full operating system manually. These stemcells reference images of Windows Server 2012 R2 hosted on public IaaSes.

Light stemcells are available for Microsoft Azure, AWS, and GCP, which typically bill a surcharge for the associated Windows licensing cost. See the documentation on those IaaSes for details.

Below is IaaS-specific documentation for light stemcells you can use with the PAS for Windows 2012R2 tile:

Stemcell Builds

Because of the constraints placed on the distribution of Windows OS by Microsoft’s licensing terms, operators must build stemcells for on-premise deployments from OS disk images (e.g. ISO files) licensed to them directly from Microsoft. This typically involves starting a Windows virtual machine, installing the BOSH agent and associated software, then exporting its disk image and converting it to a stemcell format.

Below is IaaS-specific documentation for building stemcells for the PAS for Windows 2012R2 tile:

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