Virtual machine scale sets can be used to deploy and manage a group of identical VMs. Earlier, virtual machines supported identical instances only; this is called uniform orchestration. Now with the introduction of flexible orchestration, you can implement a scale set with identical or multiple types of VM. Though this feature is in public preview at the time of writing this book, it is worth explaining this because in the future you will see this option.
For VMSS, no pre-provisioning of the VM is required. VMSS targets major workloads such as parallel processing, big data, and containerized workloads. VMSS is being used as nodes for the Azure Kubernetes Service because of the scalability. In short, as demand grows, more instances will be added based on the rules or a schedule. You can accomplish the scaling manually or using automation.
The following are the benefits offered by VMSS:
- Under uniform orchestration, all VMs that are part of the scale set are created using the VM configuration and OS image. This makes the configuration and network management much easier.
- All VMs in a scale set will have only private IP addresses, and the scale set can be placed as a backend pool for Azure Load Balancer or Azure Application Gateway.
- Since there are multiple instances of your application, if there is an issue with one instance, customers can be redirected to another instance with minimal interruption.
- Based on the demand, the number of instances can be increased or decreased. VMSS is ideal for all kinds of unexpected demand.
- VMSS supports up to 1,000 VMs in a scale set. If you are using custom images, you can have up to 600 VMs.
Implementing a Scale Set
You can implement a scale set from the Azure portal, Azure PowerShell, the Azure CLI, and the REST API. The process is very similar to creating a virtual machine. In the Azure portal, you can search for VMSS, and you will see Virtual Machine Scale Set in the search results. Once you click it, you will be redirected to the Virtual Machine Scale Set blade; then click Create.
The Basic tab consists of basic details such as subscription, resource group, virtual machine scale set name, region, and availability zone. Using the availability zones, you can span your scale set across zones. Further, you can select the orchestration mode: Uniform or Flexible. To select Flexible mode, you need to register your subscription as this feature is in preview. Also, you will be able to configure the instance details including the image, size, authentication type, username, etc., as shown in Figure 7.10.