Is microsoft recreating PaaS VMs for Web / Worker Roles for each release?

Question

I want to understand how does this Web / Worker role under cloud service work. As per my understanding, we have to define the required Web / Worker role instance count in CSDEF file, and Azure will create VMs (Instances) under the cloud service automatically. How about the application is updated and new code is deployed? Will the existing instances destroyed and new instances will be created or only the changed code will be updated in IIS? How does it work in the backend?

Note: Basically I have four instances in a web role and I want to create around 20 local user accounts in the VMs to manage it by different teams. I want to ensure the accounts do not get deleted whenever deployment is done.

Answer 1

Basically I have four instances in a web role and I want to create around 20 local user accounts in the VMs to manage it by different teams. I want to ensure the accounts do not get deleted whenever deployment is done.

Simple answer: Don't Do This!

Azure Cloud Services are essentially Stateless Virtual Machines. What that means is that anything you do in the VM (like installing software etc.) after a VM is created for you can be removed. Though this doesn't apply when you simply deploy the new version of the code but there are times when Microsoft takes down faulty VMs and stand up new VMs for you automatically from the last package file you used to create/update the deployment. In this scenario, any changes you have made will be lost.

Answer 2

Cloud services should be considered stateless. The disks won't necessarily be destroyed on every deployment, but you must plan for it. Any configuration or operations you wish to perform prior to the role starting up must be defined as a startup task in the CSDEF file.