# Route 53 ## Icon ![Route 53](https://icon.icepanel.io/AWS/svg/Networking-Content-Delivery/Route-53.svg) ## About * A highly available, scalable, fully managed and Authoritative *(i.e., you can update the DNS records)* DNS. * `Route 53` is also a Domain Registrar and can register your domain name in the service. * It is a global service. * **The only AWS service that provides 100% availability SLA**. * Each record of the domain consists of, * Domain/SubDomain Name - *(domain name like `example.com`)*. * RecordType - *(DNS Record Types)*. * Value - *(IP addresses/DNS entry)*. * Routing Policy * TTL - *(Cache duration at DNS resolver end)*. ## Domain Registrar * Domain Registrar in AWS ecosystem is Amazon Registrar. * Domain Registrar is not same as DNS service. They may have DNS capability. ## Hosted Zone * A container for records, and records contain information about how you want to route traffic for a specific domain, such as `example.com`, and its subdomains (`acme.example.com`, `zenith.example.com`). * **A hosted zone and the corresponding domain have the same name**. * Any type of hosted zone created charges `$0.50` per month per hosted zone. And separate charged for domain registration. * There are two types of hosted zones. ### Public Hosted Zone * Contains records that specify how to route the traffic on the Internet. * Can be queried by resources anywhere on internet. ### Private Hosted Zone * Contains records that specify how to route the traffic within one or more VPCs *(private domain names)*. * Can only be queried by resources in your VPC. ## Record Types * There are several [types](https://en.wikipedia.org/wiki/List_of_DNS_record_types) of DNS records. * Some of them are as `A`, `AAAA`, `CNAME`, `NS` etc. ### CNAME * Points a hostname to any other hostname. * `CNAME` records can only be made for **non root domain**. They cannot be created for top node of DNS *(Zone Apex)*. ### Alias * Points a hostname to an AWS resource. * This is an extension specific to Route53 domain registrar. * Works for **both root and non-root domain**. * Free of charge, does not incur charges on querying. * **Cannot set `TTL` for these record, this is set automatically by Route53**. * Alias can have following target * Elastic load balancer * CloudFront Distributions * API Gateway * ElasticBeanStalk environments * S3 Websites * VPC Interface Endpoints * Global Accelerator accelerator * **Route 53 record in the same Hosted Zone**. * Note that only one target can be specified for these type of records. * Alias cannot be set for a EC2 DNS name. * Alias Records are always of type `A` or `AAAA`. * They also have native health checks support. * Underlying resource's IP address change will be recognized automatically. ## Routing Policy * A routing policy, determines how `Amazon Route 53` responds to queries. * Types of routing policy * Simple * Can only have one record for alias, does not allow health checks. * Weighted * Note that weights dont have to sum up to 100. It's just a distribution ratio. * Can be associated with health checks. * A weight of zero, means no traffic to that resource. * If all reacords have weight zero, then all records will be returned with equal weight. * Failover * Helps to achieve active-passive setup of resource. * Latency Based * Redirect to the resource closest to the requester i.e client. * Has to suppply both primary and secondary failover record type. * Health check is mandatory for primary record type. * Geolocation * This routing is based on user location, different from latency based routing. * Should have a record in case, there is no match on location. * Multi-Value * To route traffic to multiple resources * Can associate health checks and will return only ip of healthy resources. * Supports upto 8 healthy records for each multi-value query. * Can have only one IP per record for this type of routing. * Geoproximity * Route traffic based on relative geographic location of user and server. * Traffic is routed based on defined bias. * For AWS resource specify region and for non AWS resource specify latitude and longtitude. * Bias value range from -99 to 99. * IP Based * Routing based on CIDR block of ip addresses provided. * More details about types of routing policies and how to choose them can be found [here](https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/routing-policy.html). ## Health checks * Configuring health checks enables **Automatic DNS failover**. * **These health checks are only for public health resources**. * About 15 global health checkers will check for the endpoint health. * Parameters such as for healthy or unhealthy threshold *(3 by default)*, interval for health checks (*30 seconds but can be 10 seconds for fast health checks)*, protocol etc can be configured. * These health checkers support protocol such as `HTTP`, `HTTPS` and `TCP`. * If `18%` of health checkers report the endpoint is healthy, then Route53 considers the resource as healthy. * Health checks are considered good when response are of status `2xx` and `3xx`. It can also set up to setup pass/fail based on text in first 5120 bytes of the response. * Ensure the router/firewall has rules to allow incoming requests from Route 53 health checkers. * Ability to configure the global health checker from a specific region is available. * Not supported by simple routing policy. * The ip ranges of these global health checkers can be found [here](https://ip-ranges.amazonaws.com/ip-ranges.json) * Health checks are integrated with Cloud Watch metrics. ### Calculated health checks * Combine the results of multiple health checks into a single health check. * One can combine the multiple health checks using `AND`, `OR` or `NOT`. * **Upto 256 child health checks can be monitored at a time**. * Parent health check pass ratio can be configured based on the number of child health checks that have passed. ### Private resource health checks * **As Route53 health checkers are outside the VPC, they cant access private VPC or on-premise resource**. * Private resources can be configured with `CloudWatch` Metric and associate them with a `CloudWatch` Alarm. * This configured `CloudWatch` Alarm can be attached to the health checker so that health check checks the `CloudWatch` alarm itself. ## Traffic Flow * Traffic flow allows to configure complicated DNS Policy. * This feature is not included in Free tier. * It provides a visual UI editor to manage complex routing decision trees.