Deploying microservices

With their focus on statelessness and horizontal scaling, microservices work well with modern cloud environments. Nevertheless, when choosing a microservice architecture, deploying your application will tend to get more complex overall, as you will need to deploy more, different applications (all the more reason to stick with the twelve-factor app methodology).

However, each inpidual service will be easier to deploy than a big monolithic application. Depending on the service's size, it will also be easier to upgrade a service to a new runtime or to replace it with a new implementation entirely. Also, you can scale each microservice inpidually. This allows you to scale out heavily used parts of your application while keeping less utilized components cost-efficient. Of course, this requires each service to support horizontal scaling.

Deploying microservices gets (potentially) more complex when different services use different technologies. A possible solution for this problem is offered by modern container runtimes such as Docker or RKT. Using containers, you can package an application with all its dependencies into a container image and then use that image to quickly spawn a container running your application on any server that can run Docker (or RKT) containers. (Let's return to the twelve-factor app—deploying applications in containers is one of the most thorough interpretations of dependency isolation as prescribed by Factor II.)

Running container workloads is a service offered by many major cloud providers (such as AWS' Elastic Container Service, the Azure Container Service, or the Google Container Engine). Apart from that, there are also container orchestration engines such as Docker Swarm, Kubernetes, or Apache Mesos that you can roll out on IaaS cloud platforms or your own hardware. These orchestration engines offer the possibility to distribute container workloads over entire server clusters, and offer a very high degree of automation. For example, the cluster manager will take care of deploying containers across any number of servers, automatically distributing them according to their resource requirements and usages. Many orchestration engines also offer auto-scaling features and are often tightly integrated with cloud environments.

You will learn more about deploying microservices with Docker and Kubernetes in Chapter 6, Deploying Your Application in Containers.