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How Does DNS Route Traffic To Your Web Application?
How Does DNS Route Traffic To Your Web Application?
The following diagram gives an overview of how recursive and authoritative DNS services work together to route an end user to your website or application.
A user opens a web browser, enters www.example.com in the address bar, and presses Enter.
The request for www.example.com is routed to a DNS resolver, which is typically managed by the user's Internet service provider (ISP), such as a cable Internet provider, a DSL broadband provider, or a corporate network.
The DNS resolver for the ISP forwards the request for www.example.com to a DNS root name server.
The DNS resolver for the ISP forwards the request for www.example.com again, this time to one of the TLD name servers for .com domains. The name server for .com domains responds to the request with the names of the four Amazon Route 53 name servers that are associated with the example.com domain.
The DNS resolver for the ISP chooses an Amazon Route 53 name server and forwards the request for www.example.com to that name server.
The Amazon Route 53 name server looks in the example.com hosted zone for the www.example.com record, gets the associated value, such as the IP address for a web server, 192.0.2.44, and returns the IP address to the DNS resolver.
The DNS resolver for the ISP finally has the IP address that the user needs. The resolver returns that value to the web browser. The DNS resolver also caches (stores) the IP address for example.com for an amount of time that you specify so that it can respond more quickly the next time someone browses to example.com. For more information, see time to live (TTL).
The web browser sends a request for www.example.com to the IP address that it got from the DNS resolver. This is where your content is, for example, a web server running on an Amazon EC2 instance or an Amazon S3 bucket that's configured as a website endpoint.
The web server or other resource at 192.0.2.44 returns the web page for www.example.com to the web browser, and the web browser displays the page.
Types of Amazon Route 53 Health Checks
Types of Amazon Route 53 Health Checks
You can create three types of Amazon Route 53 health checks:
Health checks that monitor an endpoint
You can configure a health check that monitors an endpoint that you specify either by IP address or by domain name. At regular intervals that you specify, Route 53 submits automated requests over the internet to your application, server, or other resource to verify that it's reachable, available, and functional. Optionally, you can configure the health check to make requests similar to those that your users make, such as requesting a web page from a specific URL.
Health checks that monitor other health checks (calculated health checks)
You can create a health check that monitors whether Route 53 considers other health checks healthy or unhealthy. One situation where this might be useful is when you have multiple resources that perform the same function, such as multiple web servers, and your chief concern is whether some minimum number of your resources are healthy. You can create a health check for each resource without configuring notification for those health checks. Then you can create a health check that monitors the status of the other health checks and that notifies you only when the number of available web resources drops below a specified threshold.
Health checks that monitor CloudWatch alarms
You can create CloudWatch alarms that monitor the status of CloudWatch metrics, such as the number of throttled read events for an Amazon DynamoDB database or the number of Elastic Load Balancing hosts that are considered healthy. After you create an alarm, you can create a health check that monitors the same data stream that CloudWatch monitors for the alarm.
To improve resiliency and availability, Route 53 doesn't wait for the CloudWatch alarm to go into the ALARM state. The status of a health check changes from healthy to unhealthy based on the data stream and on the criteria in the CloudWatch alarm.
multiple endpoint can be determined as the Global level LB
https://cloudly.engineer/2019/aws-route-53-routing-policies-explained-with-diagrams/aws/
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