About Microservices.io

Microservices.io is brought to you by Chris Richardson. Experienced software architect, author of POJOs in Action, the creator of the original CloudFoundry.com, and the author of Microservices patterns.

Chris helps clients around the world adopt the microservice architecture through consulting engagements, and training classes and workshops.

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Assess your application's microservice architecture and identify what needs to be improved.

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Pattern: 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:

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

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