Part 3. Learn about AWS at once - Route53, VPC

##Route53

DNS, Records, Routing Policy, It provides control over DNS and helps you connect to your instance by forwarding its IP address. Health check of resources and 100% service level agreement (SLA) are possible. 53 is the default DNS port number.

• You can purchase a domain from a third party and register the name server with Route53. (ex. goDaddy)

DNS

It converts a hostname into an IP address that people can easily understand.

• TLD (Top Level Domain) - .com
• SLD (Second Level Domain) - .github.com
• Sub Domain - api.github.com

How DNS works

First, when a client sends a DNS request from a web browser, the local DNS server checks whether there is corresponding DNS information in its cache, converts it to an IP address, and forwards it. If not, it queries the local DNS server and receives TLD information from the Root DNS server, SLD information from the TLD DNS server, and IP address information from the SLD DNS server. In other words, it sequentially searches for information to obtain an IP, caches it in the local DNS server, and delivers the resulting IP address to the web browser. And you can connect to the web server based on this address.

Records

Records include domain/subdomain name, record type, value, routing policy, and TTL. Here, record types include A, AAAA, CNAME, NS, etc.

• A - Map hostname to IPv4
• AAAA - map hostname to IPv6
• CNAME - maps a hostname to another hostname
• NS - Name server of Hosted Zone
• Hosted Zone is a resource that acts as a container for managing domain names.
• AWS automatically assigns name servers and registers them with your domain registrar, so that DNS requests are forwarded to Route53.
• Unlike public Hosted Zones, you can also use Private Hosted Zones for queries on resources within your VPC.

####TTL TTL is used to cache information about records provided to clients. This will reduce traffic querying Route53 from clients.

nslookup api.github.com
dig api.github.com
// ANSWER SECTION

Alias

CNAME is a feature for root domains. On the other hand, unlike CNAME, Alias ​​works even when it is not a root domain. Alias ​​can respond with value of resource below. However, you cannot use EC2 DNS name as Records Target.

• Amazon API Gateway custom regional API or edge-optimized API
• Amazon VPC interface endpoint
• A CloudFront distribution
• Elastic Beanstalk environment
• Elastic Load Balancing load balancer
• AWS Global Accelerator accelerator
• Amazon S3 bucket configured with a static website
• Other Route 53 records of the same type in the same hosted zone.
• AWS AppSync domain name

Routing Policy

You can specify routing policies to determine how Route53 responds to queries. You can also create it through Traffic Policy, in which case you can check it with more visualized data when setting it up.

• Simple routing policy
• Failover routing policy
• According to the health-check results, if the resource is normal, connection can be made. If it is unhealthy, connection is made according to the secondary setting of the resource.
• Geolocation routing policy
• Routing policy based on user location.
• Geoproximity routing policy
• Routing policy based on resource location.
• Depending on the bias, you can set it so that more users can be routed to that resource. -Latency routing policy
• This is a policy that allows redirection to a nearby ALB.
• IP-based routing policy
• Use when routing traffic based on the user's location and the IP address from which the traffic originates.
• Multivalue answer routing policy
• Used to respond to DNS queries by randomly selecting up to 8 normal records.
• Weighted routing policy
• Set the weight to determine what percentage of requests will be sent to a specific resource.
• If all weight values ​​are 0, resources will be distributed in equal % across requests.

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VPC

A virtual private network allows partitioning within a VPC into subnets. Internet Gateway also provides access to subnets in your VPC. However, if you want to access a private subnet, you can access Internet Gateway through NAT Gateway.

• Shows network traffic logs using VPC Flow log.
• VPC Peering
• The two VPCs will be able to communicate with each other using their private IP addresses.
• The connection is unidirectional and targets one Peering VPC.
• Also, when connecting, the CIDR blocks (ex. 192.168.1.0/24) of the two VPCs must not overlap.
• VPC Endpoint
• You can connect to S3 or DynamoDB using VPC Endpoint Gateway.
• Using the VPC Endpoint Interface, you can connect to services such as Cloudwatch.
• Site to Site VPN is an encrypted connection over the Internet, while Direct Connect is a physical connection that is secure and fast, but can take months to deploy.