Let me start by painting a picture. You are using Azure. You have an App Service configured with a Web App that is hosting a website; this website for example. The website could be single-instanced or it could be multi-instanced using Azure Load Balancer, Azure Traffic Manager, Azure Application Gateway, or any other number of load balancing and traffic distribution technologies. One day, your web application fails to respond and you get a dreaded HTTP 500 or another error code. As a dedicated Azure consumer, you use Azure Application Insights to monitor your website. Application Insights not only gives you user metrics akin to Google Analytics but also gives you performance and availability metrics.
The picture I painted just then explains my scenario. I use Azure App Service with an Azure Web App to host this blog. I use Azure Application Insights to provide me with all of the metrics and data I need to understand the site. The availability monitoring feature is quite excellent. It allows me to monitor the website availability from up to five locations around the world with performance data for each region so I can see how the site performs for each geography. If the site goes down for any reason, I get an email notification to warn me.