Twelve-Factor App | Scale out via the Process Model

The eighth factor of the Twelve-Factor App methodology emphasizes scaling out via the process model. 

Why Scale-Out via the Process Model?

Scaling out (horizontal scaling) involves adding more process instances to handle the increased load. This approach offers several advantages:

  • Scalability: Adding more instances enables the system to handle more traffic.
  • Resilience: Provides fault tolerance by distributing the load across multiple instances.
  • Flexibility: Allows for fine-grained control over scaling based on specific needs.

How to Scale Out via the Process Model

Design for Concurrency

Applications must be designed to run as independent processes that can be scaled horizontally.

Example: Stateless REST API

Design a RESTful API that doesn't rely on local state, allowing for easy scaling.

Utilize Orchestration Tools

Tools like Kubernetes enable automatic scaling based on demand.

Example: Kubernetes Horizontal Pod Autoscaler
apiVersion: autoscaling/v2beta2
kind: HorizontalPodAutoscaler
  name: myapp
    apiVersion: apps/v1
    kind: Deployment
    name: myapp
  minReplicas: 3
  maxReplicas: 10
Monitor and Adjust Scaling

Use monitoring tools to observe performance and adjust scaling as needed.

Deployment Strategies with Concurrency

Managing concurrency is essential for handling varying loads.

  • Development Stage: Design the application for horizontal scaling.
  • Deployment Stage: Use orchestration tools to automate scaling.
  • Monitoring Stage: Continuously monitor performance and adjust scaling rules as necessary.

Scaling out via the process model is fundamental to building resilient, scalable applications.