What is Auto-Scaling in SaaS?

Auto-scaling is a feature that adjusts a SaaS application’s resources up or down based on current usage. When there are more users, auto-scaling increases available resources – on the flip side, it decreases them during quiet periods. 

SaaS companies need auto-scaling because they often don’t know when traffic is going up or down. While it’s sometimes predictable (e.g. a product launch), sudden global events and unexpected spikes are where auto-scaling should be deployed.

Reasons why you must use auto-scaling in your SaaS business include: 

• Performance: Use auto-scaling so that your site or app works optimally during busy periods; without it, you could encounter service disruptions. 
• Availability: You need to implement auto-scaling so customers can access your site, product, and services 24/7.
• Cost Optimization: Use auto-scaling to scale up and down based on real-time usage – you risk needless expenses if you use an alternative method.

Metrics used to trigger auto-scaling include: 

• CPU Utilization: The amount of CPU being used at any given time.
• Memory Usage: How much memory an app or website is using in real-time.
• Network Traffic: Incoming and outgoing site visitors and app users.
• Request Latency: Response times to user requests; this depends on how many users are on the same server. 
• Queue Length: Pending queue requests; auto-scaling up is triggered when this is higher.

Different auto-scaling policies work in varying scenarios. Here’s a list of some common ones and when you should use them: 

• Target Tracking: Moves resources based on a metric like average queue lengths; use when you know your workloads. 

• Step Scaling: Scales within thresholds you set; use if you’re a beginner.

• Scheduled Scaling: Scales based on scheduled times; use if you know daily or weekly traffic patterns.

Examples of SaaS companies that use auto-scaling based on demand are: 

• Shopify: Sets parameters to auto-scale resources during high-traffic times, such as Black Friday and the Holiday Season.

• Slack： Considers peak messaging times (e.g. work hours) to allocate resources as needed.

• Netflix: Auto-scaling parameters are set to manage traffic when more viewers are online (e.g. evenings and weekends).