Answer: B.
Since the mission-critical applications require 99.999% uptime, I would need an Active-Active site replication of resources.
Here one site's failure will result in Route 53 automatically switching to the other site, thus maintaining the uptime requirement.
Option A is incorrect.
Multivalve answer routing provides the ability to return multiple health-checkable IP addresses, which is a way to use DNS to improve availability and load balancing.
The critical point here is that these IP addresses may not point to servers at multiple site locations.
Rather they may be servers in different availability zones within the same region.
Since we add a higher level of resiliency for the critical requirement, it's always advisable to provide an entire region failure.
Option B is CORRECT.
Failover routing is usually used in Disaster Recovery scenarios where an Active-Passive or Active-Active Disaster recovery configuration is required.
Option C is incorrect.
A weighted routing policy is usually used to route traffic in proportions that are specified.
E.g., if there is a new version of software that needs to be tested, 20% of the traffic can be sent to that site for getting user feedback rather than sending 100% of the traffic to that site.
Option D is incorrect.
A simple routing policy is used for routing traffic to a single resource, e.g., mapping an URL to a web server.
Diagram:
Reference:
https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/routing-policy.html
The routing policy that should be applied while using Route 53 to ensure 99.999% uptime for a mission-critical application is Multi Value Answer (MVA) Routing.
MVA Routing is a routing policy provided by Route 53 that is designed to improve the availability and latency of your applications. It allows you to specify multiple IP addresses or multiple values for a single resource record set, and Route 53 responds to DNS queries with up to eight healthy IP addresses or values for the same record. This allows Route 53 to return multiple IP addresses for a given hostname, improving availability and fault tolerance by making it easier to route traffic to the healthy endpoints.
In addition, MVA Routing also includes health checks to monitor the health of the endpoints associated with the record set. If an endpoint becomes unhealthy, Route 53 will stop including that endpoint in the response to DNS queries, and will only include the healthy endpoints. This ensures that traffic is only routed to healthy endpoints, improving the availability of your application.
Failover Routing is another routing policy that can be used to improve availability, but it is typically used in scenarios where there are two different endpoints that are serving traffic, such as a primary and secondary site. Weighted Routing is used when you want to route traffic to different resources in proportions specified by you. Simple Routing is the default routing policy, which is used when you only have one resource that serves traffic.
Therefore, Multi Value Answer (MVA) Routing is the most appropriate routing policy to ensure 99.999% uptime for a mission-critical application hosted on AWS.
