AZ-204 Developing Solutions for Microsoft Azure Exam

Understand and Configure Azure Autoscale for Apps and Services

Autoscale is an Azure feature that automatically adjusts the number of App Service plan instances based on demand. With horizontal scaling, it adds or removes instances when resource use crosses thresholds, helping to improve availability and minimize costs. Autoscale relies on rules that specify when to scale and by how many instances, and it can scale out (increase instances) or scale in (decrease instances). By responding to real‐time metrics and schedules, autoscale ensures web apps remain responsive during peak times without over-provisioning during low usage.

Azure autoscale supports horizontal scaling but not vertical scaling in web apps. Horizontal scaling changes the instance count, whereas vertical scaling adjusts the CPU, memory, or storage of existing instances. Vertical scaling is done by scale up operations, which require changing the pricing tier of the App Service plan. Since vertical scaling has hardware limits and may require restarts, horizontal scaling is more flexible and faster for dynamic web workloads.

To configure autoscale for an Azure App Service Web App, you define profiles of rules, capacity, and schedules in the Azure portal or via CLI. Metric-based scaling uses metrics like:

• Percentage CPU
• Memory usage
• HTTP queue length
• Custom metrics via Application Insights
  You set a low and high threshold, and the system uses OR logic to trigger scale out and AND logic for scale in. Each profile specifies a minimum, maximum, and default instance count to keep scaling within safe bounds.

You can also add time-based scaling rules to prepare for known traffic patterns, such as weekends or special events. Schedule-based rules let you scale to a specific instance count for certain days or date ranges, ensuring capacity matches anticipated load. Autoscale can send notifications via email or webhooks when scaling actions occur, which helps in monitoring and auditing changes. Best practices include defining at least one scale-out and one scale-in rule and testing thresholds to avoid rapid scaling cycles.

Conclusion

In summary, Azure autoscale for App Service helps web apps stay available by automatically adjusting instance counts based on real‐time metrics and scheduled events. By focusing on horizontal scaling through scale-out and scale-in operations, apps can handle varying loads without manual intervention or excessive cost. Setting clear rules, thresholds, and schedules ensures predictable performance and resource use. Remember to monitor notifications and test your scaling logic to maintain reliability and efficiency.