Pattern: Multiple service instances per host

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

Run multiple instances of different services on a host (Physical or Virtual machine).

There are various ways of deploying a service instance on a shared host including:

• Deploy each service instance as a JVM process. For example, a Tomcat or Jetty instances per service instance.
• Deploy multiple service instances in the same JVM. For example, as web applications or OSGI bundles.

Examples

Resulting context

The benefits of this pattern include:

• More efficient resource utilization than the Service Instance per host pattern

The drawbacks of this approach include:

• Risk of conflicting resource requirements
• Risk of conflicting dependency versions
• Difficult to limit the resources consumed by a service instance
• If multiple services instances are deployed in the same process then its difficult to monitor the resource consumption of each service instance. Its also impossible to isolate each instance

Related patterns

• The Single Service Instance per Host pattern is an alternative solution.
• The Serverless deployment pattern is an alternative solution.