If this is a cloud deployment, there might be a recommended method native to your cloud if you search for <your cloud provider> synthetic monitoring or <your cloud provider> canary.
Before resorting to Synthetics, you can use Cloudwatch to setup anomaly reporting on the load balancer. If your requests drop to 0 in 5/10/15 minutes, alert... If you have more than N 500s in 5/10/15 minutes, alert.
Synthetics are there to tell you when something outside of your provider is breaking your website, like routing errors, geo-related issues, CDN issues (assuming you're not using your provider's CDN).
Synthetics are there to tell you when something outside of your provider is breaking your website, like routing errors, geo-related issues, CDN issues (assuming you're not using your provider's CDN).