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Pattern: Service Instance per VM

Context

You have applied the Microservice architecture pattern and architected your system as a set of services. Each service is deployed as a set of service instances for throughput and availability.

Problem

How are services packaged and deployed?

Forces

  • 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 deployment to reliable
  • You must deploy the application as cost-effectively as possible

Solution

Package the service as a virtual machine image and deploy each service instance as a separate VM

Examples

  • Netflix packages each service as an EC2 AMI and deploys each service instance as a EC2 instance.

Resulting context

The benefits of this approach include:

  • Its straightforward to scale the service by increasing the number of instances. Amazon Autoscaling Groups can even do this automatically based on load.
  • The VM encapsulates the details of the technology used to build the service. All services are, for example, started and stopped in exactly the same way.
  • Each service instance is isolated
  • A VM imposes limits on the CPU and memory consumed by a service instance
  • IaaS solutions such as AWS provide a mature and feature rich infrastructure for deploying and managing virtual machines. For example,
    • Elastic Load Balancer -
    • Autoscaling groups

The drawbacks of this approach include:

  • Building a VM image is slow and time consuming

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