add concepts page.

Author: nullfunc

docs/concepts/scaling.md

@@ -0,0 +1,66 @@
+---
+title: Scaling
+description: Defang can help you handle service irregular loads.
+sidebar_position: 375
+---
+
+# Scaling
+
+Scaling is the process of adjusting the number of instances (or replicas) of a service to meet the current demand. Services that receive requests—such as APIs, workers, or background jobs—can be scaled up or down to optimize performance, availability, and cost.
+
+Scaling is a core concept in distributed systems and cloud-native applications. It ensures your system can handle varying workloads without degrading user experience or over-provisioning resources.
+
+## Why Scale?
+
+Scaling enables services to respond effectively under different conditions:
+
+- **High Traffic**: When demand spikes, scaling up ensures your service can process more requests in parallel.
+- **Cost Optimization**: Scaling down during periods of low demand helps reduce unnecessary resource usage and cloud costs.
+- **Fault Tolerance**: Multiple instances of a service provide redundancy in case of instance failure.
+- **Throughput & Latency**: Additional instances can reduce response times and increase the number of operations your service can perform per second.
+
+## Types of Scaling
+
+There are two main ways to scale a service:
+
+- **Horizontal Scaling**: Adds or removes instances of a service. This is the most common approach for stateless services.
+- **Vertical Scaling**: Increases or decreases the resources (CPU, memory) available to a single instance.
+
+In most modern deployments, horizontal scaling is preferred because it aligns well with cloud-native principles and is easier to automate and distribute.
+
+## Auto-Scaling
+
+**Auto-scaling** refers to automatically adjusting the number of service instances based on defined policies or metrics.
+
+Instead of manually adding more instances when traffic increases, an auto-scaling system watches key indicators (like CPU usage) and takes action in real time.
+
+### How It Works
+
+Auto-scaling systems typically rely on:
+
+- **Metrics Collection**: Real-time monitoring of system metrics.
+- **Scaling Policies**: Rules that define when to scale up or down. For example:
+  - If average CPU > 85% for 5 minutes → scale up by 2 instances.
+- **Cooldown Periods**: Delays between scaling events to prevent rapid, repeated changes (flapping).
+
+### Supported Platforms
+
+| Platform        | Auto-Scaling Support |
+|----------------|----------------------|
+| AWS            | ✅ Supported         |
+| GCP            | ✅ Supported         |
+| DigitalOcean   | ❌ Not yet supported |
+
+> 💡 We're actively working on support for additional platforms. Let us know which ones you’d like to see next! 
+
+### Benefits of Auto-Scaling
+
+- **Elasticity**: Automatically adapts to changing workloads.
+- **Resilience**: Helps maintain performance during traffic surges or partial outages.
+- **Efficiency**: Reduces the need for manual intervention or over-provisioning.
+
+### Considerations
+
+- Ensure services are **stateless** or use **externalized state** (e.g., databases, caches) for smooth scaling. ([12 Factor App](https://12factor.net/processes))
+- Test services under load to identify scaling bottlenecks.
+  

docs/tutorials/scaling-your-services.mdx

@@ -83,13 +83,13 @@ Once deployed, your services' CPU usage is monitored for how much load it is han
 
 Requirements
 
-- BYOC, your own cloud platform account (AWS or GCP).
-- You must be on the Pro or higher plan to use autoscaling.
+- BYOC, your own cloud platform account. ([Scaling](/docs/concepts/scaling))
+- You must be on the Pro or higher plan to use autoscaling. ([Defang plans](https://defang.io/#pricing))
 - Only staging and production deployment modes supported. ([Deployment modes](/docs/concepts/deployment-modes))
 - The service must be stateless or able to run in multiple instances.
 - Only CPU metrics are used for scaling decisions.
 
 Best Practices
 
-- Design your services to be horizontally scalable.
+- Design your services to be horizontally scalable. ([12 Factor App](https://12factor.net/processes))
 - Use shared or external storage if your service writes data. (e.g. Postgres or Redis [managed services](/docs/concepts/managed-storage) )