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How can I use microservices and containers to build an app?

We want to scale down one of our large applications. What role do containers play in a microservices-based app, and what other services do I need?

Containers are basically low-overhead virtual machines. But unlike traditional hypervisor-based VMs, containers all exist on top of a container orchestration platform, such as Docker or Kubernetes, and share a common OS kernel. This means containers can be created, scaled up, managed and destroyed very quickly; they're then grouped or connected through APIs.

Consequently, containers have emerged as an extraordinarily useful tool in microservices application development. Major public cloud providers, such as Amazon EC2 Container Service, Google's Container Engine and Azure, now support container services.

However, it's important to point out the distinction between microservices and containers. Containers are one of many tools developers can use to package and deploy components used for microservices applications. The idea is to choose services for an application based on the problems developers are trying to solve.

For example, containers may be entirely appropriate for microservices applications that demand high levels of performance scalability -- ability to spin up additional functional components to support periods of higher demand. But the technical reality that containers share a common server OS may make containers unsuitable for microservices applications, where security is a primary concern -- at least until containers evolve to provide better isolation between instances.

Additional services are usually required to make a complete AWS microservices application. Developers should implement more resources to fully support an application composed of microservices and containers -- such as storage through Amazon S3, event-driven computing through AWS Lambda functions and application traffic management with AWS Elastic Load Balancing. With an application based on microservices and containers, developers have the flexibility to select services that best fit the functional requirements of each component. The components are then stitched together using a common API, so each functional component works together. But each container or component is independent from the others.

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