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Cloud Services is a platform as a service (PaaS) compute feature in which applications are deployed into instances (managed virtual machines) of server types referred to as web roles and worker roles. The deployment of the instances is fully managed by Microsoft, making it easy to scale applications in and out.

After writing your application, you create a deployment package for your application and upload it to Azure; Azure will create the requested number of VMs and install your software on them. Azure manages the VMs, bringing up new instances if one crashes, and handling the updates without downtime. Azure also manages the load balancing and autoscaling for the VMs. You can easily change the number of VMs by modifying the instance count in the classic Azure portal. If you increase the instance count, Azure takes the original deployment package and deploys additional instances. If you decrease the instance count, Azure shuts down and removes instances.

Cloud Services web and worker roles are classic resources, and can only be used with the classic version of resources such as virtual networks and storage accounts. The Resource Manager deployment model is the recommended deployment model moving forward in Azure. For Cloud Services, the recommendation is to use other parts of Azure to run these kinds of workloads. New web workloads are better handled by the App Service feature. The worker roles that loop infinitely and do work such as reading messages from a queue can be migrated to WebJobs or the new Service Fabric product.

Source of Information : Microsoft Azure Essentials Fundamentals of Azure Second Edition