Compare App Service and Container Apps for a small service

You are planning a small service and need to decide between Azure App Service and Azure Container Apps. The choice often comes down to whether you want to optimise for web application hosting or container-based microservices. Both options are fully managed, but they serve different architectural patterns.

Understand the core hosting models

Azure App Service provides fully managed hosting for web applications, including websites and web APIs. It is optimised for web applications and supports deployment using code or containers. When building web apps, App Service is an ideal option because it integrates seamlessly with other Azure services and offers a familiar development experience for traditional web workloads. You can deploy your application using code, which is often simpler for standard web frameworks, or use containers if you need specific runtime dependencies.

Azure Container Apps, on the other hand, enables you to build serverless microservices and jobs based on containers. It is optimised to run general-purpose containers, especially for applications that span many microservices deployed in containers. Container Apps is powered by Kubernetes and open-source technologies like Dapr, KEDA, and Envoy. It supports Kubernetes-style apps and microservices with features like service discovery and traffic splitting. However, it does not provide direct access to the underlying Kubernetes APIs. If you require direct access to the Kubernetes APIs and control plane, you should use Azure Kubernetes Service instead.

Compare scaling and operational features

Scaling is a key differentiator. Azure Container Apps supports event-driven application architectures by enabling scale based on traffic and pulling from event sources like queues. It also supports scale to zero, which means your application can scale down to zero instances when not in use, reducing costs. Applications that scale on CPU or memory load cannot scale to zero. Container Apps also supports running on-demand, scheduled, and event-driven jobs.

Azure App Service provides autoscaling capabilities, but the features available depend on the pricing tier. Basic App Service does not provide every autoscale feature, and shared App Service compute is not absence of all tenant isolation. Extra separate plans do not inherently save cost. App Service is generally always-on, which can be beneficial for applications that require consistent low-latency responses but may result in higher costs during idle periods.

Consider deployment and management complexity

Deployment complexity varies between the two options. With Azure App Service, you can deploy using code or containers, and it integrates with other Azure services. It is a good choice if you are already familiar with the App Service environment and want a straightforward deployment process. Container Apps requires you to package your application in a container, but it provides built-in support for HTTPS or TCP ingress without managing other Azure infrastructure. It also supports running multiple container revisions and managing the container app’s application lifecycle.

Container Apps provides many application-specific concepts on top of containers, including certificates, revisions, scale, and environments. Users often interact with Azure Container Instances through other services, but Container Apps provides a more opinionated approach that aligns with microservices architectures. If you need a less “opinionated” building block that doesn’t align with the scenarios Azure Container Apps is optimising for, Azure Container Instances is an ideal option.

Make a decision based on your requirements

If you are building a web application and want a fully managed hosting solution with straightforward deployment, Azure App Service is likely the better choice. It is optimised for web applications and integrates well with other Azure services. If you are building a microservices architecture or need event-driven scaling, Azure Container Apps is more suitable. It provides advanced features like service discovery, traffic splitting, and scale to zero, which are beneficial for container-based applications.

To verify your choice, consider the following:

• Do you need to deploy containers or can you use code?
• Do you require event-driven scaling or scale to zero?
• Are you comfortable with Kubernetes-style concepts like revisions and service discovery?
• Do you need direct access to Kubernetes APIs?

If you answer yes to the first three questions and no to the last, Azure Container Apps is likely the right fit. If you answer no to the first three and yes to the last, you should consider Azure Kubernetes Service. For most small web applications, Azure App Service remains a strong candidate due to its simplicity and integration capabilities.

For a small service, start by deploying a simple web application to both environments if possible, or use the quickstarts provided by Microsoft to understand the deployment process. This hands-on approach will help you determine which option best fits your operational requirements and team expertise.

References for Compare App Service and Container Apps for a small service: Comparing Container Apps with other Azure container options, Azure Container Apps overview, Azure Functions overview.