Developing client-server applications has resulted in a focus on building tiered applications that use specific technologies in each tier and is typically divided by functional layers such as front end, business logic, and data storage. Such applications are often referred to as monolithic applications and are packaged onto hardware scaled upfront to cater for worst case scenarios or peak loads. The main drawbacks of this development approach are the tight coupling between components within each tier, that individual components cannot be easily scaled as well as the infrastructural cost of the multiple environments needed to build, test, and run the application. A simple update can have unforeseen effects on the rest of the tier, and so a change to an application component requires its entire tier to be retested and redeployed which severely reduces the agility of the business. An additional significant concern facing businesses in the digital age is that monolithic applications can't be easily scaled. A monolithic application is scaled by cloning the entire application stack onto multiple machines which is costly and difficult to provision and manage.

A container is a modified runtime environment built on top of a host operating system that executes your application. A container does not use virtualization, so it does not waste resources simulating virtual hardware with a redundant operating system. This typically makes containers significantly more lightweight than VMs. This design allows you to respond quickly to changes in demand or failure. Another benefit of containers is you can run multiple isolated applications on a single container host as since containers are secured and isolated, you do not need separate servers for each app and are key enablers of microservices.

Microservices offer a different approach to application development and deployment, an approach that is suited to the agility, scale, and reliability requirements of modern cloud applications. A microservices application is decomposed into independent components that work together to deliver the application's overall functionality. The term microservice emphasizes that applications should be composed of services small enough to reflect independent concerns, so that each microservice implements a single function. In addition, each microservice has well-defined contracts so that other microservices can communicate and share data with it. Microservices can scale-out independently, as compared to monolithic applications that scale together. This means that a specific functional area, that requires more processing power or network bandwidth to support demand can be scaled rather than unnecessarily scaling-out other areas of the application. Some of the benefits of using microservices are: Each microservice is relatively small, easy to manage and evolve. Each microservice can be developed and deployed independently of other services. Each microservice isolates any issues. For example, if there is an issue in a service it only impacts that service. The other services can continue to handle requests. Each microservice can use the latest technologies. Because microservices are autonomous and run side-by-side, the latest technologies and frameworks can be used, rather than being forced to use an older framework that might be used by a monolithic application.

The task of automating, managing, and interacting with many containers is known as orchestration. Keeping containerized apps up and running can be complex because they often involve many containers deployed across different machines. Kubernetes is open-source orchestration software for deploying, managing, and scaling containers. Kubernetes has become the de facto choice globally for container orchestration and is supported by all the major technology vendors. Azure Kubernetes Service (AKS) is Microsoft’s PaaS service for Kubernetes on Azure and is a complete orchestration service for containers with distributed architectures with multiple containers.