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Pattern: Service instance per container

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 (Docker) container image and deploy each service instance as a container

Examples

Docker is becoming an extremely popular way of packaging and deploying services. Each service is packaged as a Docker image and each service instance is a Docker container. There are several Docker clustering frameworks including:

Resulting context

The benefits of this approach include:

  • It is straightforward to scale up and down a service by changing the number of container instances.
  • The container 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 container imposes limits on the CPU and memory consumed by a service instance
  • Containers are extremely fast to build and start. For example, it’s 100x faster to package an application as a Docker container than it is to package it as an AMI. Docker containers also start much faster than a VM since only the application process starts rather than an entire OS.

The drawbacks of this approach include:

  • The infrastructure for deploying containers is not as rich as the infrastructure for deploying virtual machines.

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