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:

• Kubernetes

• Marathon/Mesos

• Amazon EC2 Container Service

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.

Related patterns

• This pattern is a refinement of the [[Service Instance per Host]] pattern

• The [[Service Instance per VM]] pattern is an alternative solution

• The [[Serverless deployment]] pattern is an alternative solution.