Multiple Service instances 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

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.