Route 53 and DNS: names instead of addresses

Why names exist

You have already leaned on hostnames without examining them: the S3 URL in lesson 4-1, and the load balancer, whose public address AWS hands you as a name, not a number. Next unit's database does the same. Time to look at the machinery.

DNS (Domain Name System) is the internet's name-lookup service: given a hostname like myapp.com, it returns the current IP address. It exists because addresses change constantly — servers get replaced, load balancers move, databases fail over to a standby — and every config file that stored the name keeps working through all of it, while every config file that stored the number breaks. That is the working rule: configure names, let DNS resolve the number at the last moment.

A lookup is called resolving a name, and the software that does it (built into every OS and browser) is a resolver.

Records, TTLs, and Route 53

Each row in that table is a record. The two you will actually touch:

• An A record maps a name to an IP address: myapp.com → 3.91.44.10.
• A CNAME record maps a name to another name: www.myapp.com → myapp.com. This is how you point at AWS resources whose IPs you never learn, like a load balancer.

Every record carries a TTL (time to live): the number of seconds a resolver may cache the answer before it must ask again. TTLs exist because the world cannot re-ask DNS on every request — caching keeps lookups fast and cheap. The trade-off is staleness: with a TTL of 86,400 (one day), a changed record keeps serving the old address from caches for up to a day. Records that must move fast, like a database endpoint that fails over, use short TTLs.

Route 53 is AWS's DNS service (named for port 53, where DNS listens). You buy or import a domain, it hosts your records for $0.50 per month per domain, and its alias records point straight at AWS resources — a load balancer, a CloudFront distribution — tracking their addresses for you.