Pattern: Service Instance per VM

pattern   deployment  

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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

Related patterns

• This pattern is a refinement of the Single Service per Host pattern
• The Service Instance per Container pattern is an alternative solution
• The Serverless deployment pattern is an alternative solution.