> For the complete documentation index, see [llms.txt](https://gia-duong-duc-minh.gitbook.io/notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gia-duong-duc-minh.gitbook.io/notes/computer/microservices/service-instance-per-vm.md).

# 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

## 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.