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.
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