A hosted service was previously a service in Azure that could contain Web Roles, Worker Roles and VM Roles.
With the new Virtual Machine (persistent) in Azure, you can also add them to a cloud service so that they can communicate in their private network.
A cloud service is automatically created when you create a virtual machine. When you create your second virtual machine you will be able to add the virtual machine to the same cloud service to enable network communication, load-balancing and maintain high availability for those virtual machines.This is important to know if you’re planning to extend your infrastructure and create connectivity between resources on-premise and in Windows Azure. Instead of going through the external IP/DNS name, you can take advantage of this private network.
So let’s repeat the PaaS service model in Windows Azure
A hosted service in Windows Azure was basically a combination of code and configuration. This does still apply for the cloud service.A cloud service represents the PaaS service model in Azure, where you can deploy your multi-tier applications, using multiple roles and have a flexible model to scale your stateless applications.
Each role (Web or/and Worker Role) has its own code and configuration file.So from a developer’s perspective, they only need to concentrate on their code, and let Windows Azure’s eco-system take care of the underlying architecture for the infrastructure and maintain performance, patching of the operating system and general maintenance in case of a failure.
Based on the SLA’s available in Azure, you must specify at least two instances of each role to assure you meat a satisfied SLA. This will apply to both failures and when you’re servicing your service.
This is to guarantee external connectivity to your internet-facing roles 99.95% of the time.
If you have worked with System Center 2012 – Virtual Machine Manager, you may be aware of the service concept where you can deploy distributed applications, use load balancing and scale out the stateless instances, and specify upgrade domains. Windows Azure has something similar, and provides you with two environments.
The staging environment is where you can test your cloud service before you put it into your production environment. When you are satisfied with your service, you can easily do a VIP swap (swapping the virtual IP address that’s associated with the two environments).
I’ll blog more about Azure over the next weeks.