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# Single Service instance per host

## 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

Deploy each single service instance on its own host

## Examples

## Resulting context

The benefits of this approach include:

* Services instances are isolated from one another
* There is no possibility of conflicting resource requirements or dependency versions
* A service instance can only consume at most the resources of a single host
* Its straightforward to monitor, manage, and redeploy each service instance

The drawbacks of this approach include:

* Potentially less efficient resource utilization compared to \[\[Multiple Services per Host]] because there are more hosts

## Related patterns

* The \[\[Multiple Service Instances per Host]] pattern is an alternative solution
* The \[\[Service Instance per VM]] pattern is a refinement of this pattern
* The \[\[Service Instance per Container]] pattern is a refinement of this pattern
* The \[\[Serverless deployment]] pattern is an alternative solution.