Our team is migrating a legacy database and web app to the cloud. How does auto-scaling work in cloud infrastructure when choosing between vertical and horizontal methods? We want to ensure we don't hit architectural limits or experience unnecessary application downtime during peak usage hours.
3 answers
Vertical scaling, or scaling up, involves adding more power—such as upgrading to a faster CPU or increasing RAM—to an existing virtual machine. Horizontal scaling, or scaling out, adds more individual machine instances to your resource pool instead. While vertical scaling is straightforward, it usually requires a reboot, creating downtime, and hits a hard hardware ceiling. Horizontal scaling offers virtually unlimited elasticity and seamless availability because instances are added behind a load balancer without disrupting operational services.
What specific database engine are you migrating, since many relational databases struggle with horizontal write scaling compared to stateless web applications?
Vertical scaling changes the size of a single instance, whereas horizontal scaling adds more instances. Horizontal is preferred for web tiers to achieve high availability.
Spot on. It is also worth noting that horizontal scaling improves fault tolerance. If one instance fails, the load balancer redirects traffic to the others, whereas a failure in a vertically scaled single instance results in a complete outage.
If you are migrating a traditional relational database like MySQL or PostgreSQL, vertical scaling is often the initial path because maintaining data consistency across multiple write instances is complex. However, for the web application tier, horizontal scaling is highly recommended as it allows stateless nodes to spin up or down freely without affecting the database layer.