Tuesday, May 10, 2022

Pattern: Single Service Instance per Host


How are services packaged and deployed?


  • Services are written using a variety of languages, frameworks, and framework versions
  • Each service consists of multiple service instances for throughput and availability
  • Service must be independently deployable and scalable
  • Service instances need to be isolated from one another
  • You need to be able to quickly build and deploy a service
  • You need to be able to constrain the resources (CPU and memory) consumed by a service
  • You need to monitor the behavior of each service instance
  • You want the deployment to reliable
  • You must deploy the application as cost-effectively as possible.


Another way to deploy your microservices is the Service Instance per Host pattern. When you use this pattern, you run each service instance in isolation on its own host. 

There are two different specializations of this pattern: Service Instance per Virtual Machine and Service Instance per Container.

Service Instance per Virtual Machine Pattern

When you use Service Instance per Virtual Machine pattern, you package each service as a virtual machine (VM) image such as an Amazon EC2 AMI. 

Each service instance is a VM (for example, an EC2 instance) that is launched using that VM image. The following diagram shows the structure of this pattern:

This is the primary approach used by Netflix to deploy its video streaming service. Netflix packages each of its services as an EC2 AMI using Animator. Each running service instance is an EC2 instance.

Service Instance per Container Pattern

When you use the Service Instance per Container pattern, each service instance runs in its own container. Containers are a virtualization mechanism at the operating system level. 

A container consists of one or more processes running in a sandbox. From the perspective of the processes, they have their own port namespace and root filesystem. You can limit a container’s memory and CPU resources. Some container implementations also have I/O rate limiting. 

Examples of container technologies include Docker and Solaris Zones. The following diagram shows the structure of this pattern:

To use this pattern, you package your service as a container image. A container image is a filesystem image consisting of the applications and libraries required to run the service. 

Some container images consist of a complete Linux root filesystem. Others are more lightweight. To deploy a Java service, for example, you build a container image containing the Java runtime, perhaps an Apache Tomcat server, and your compiled Java application.

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