The correct option is Scale the App Service plan up to a higher SKU such as Premium V3.

Scale the App Service plan up to a higher SKU such as Premium V3 is the right choice because the repeated HTTP 503 errors point to the application exhausting CPU and memory on the existing App Service plan. Moving to a higher SKU provides more vCPUs and more memory per instance and often faster underlying hardware, which directly addresses resource exhaustion on each instance without changing the application architecture.

Create an Azure Content Delivery Network endpoint is incorrect because a CDN mainly caches static content and reduces bandwidth and latency for clients. A CDN will not increase CPU or memory available to the web application processes on the origin App Service and so it will not resolve 503s caused by instance resource exhaustion.

Enable the App Service Local Cache feature is incorrect because Local Cache creates a read only copy of site files in memory to reduce file I O and improve cold start behavior. It does not add CPU cores or increase the memory available to the App Service process in a way that resolves sustained CPU or memory exhaustion across the application workload.

Add an App Service staging deployment slot is incorrect because deployment slots provide deployment and testing benefits and can help with warm up before swapping. A staging slot runs in the same App Service plan and shares the same instance resource limits unless you move it to a different plan. Creating a slot therefore does not increase the CPU or memory available to the production application and will not fix 503s caused by resource limits.

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