CNAME レコード
Aliases one hostname to another — the resolver follows it transparently.
CNAME レコードとは?
A CNAME (Canonical Name) record makes one hostname an alias of another. Resolvers chase the chain until they find an A/AAAA and return that. It is the standard way to point custom subdomains at CDN or PaaS hostnames (Cloudflare, Vercel, Netlify, AWS).
ゾーンファイルの例
www.example.com. 300 IN CNAME example.netlify.app.
代表的な用途
- ▸Point www → apex without managing IPs.
- ▸Custom domain → SaaS provider hostname (Vercel, Netlify, Heroku, GitHub Pages).
- ▸Custom CDN endpoint → CloudFront / Cloudflare / Bunny.
- ▸Service decoupling — change the upstream by editing one CNAME.
よくある落とし穴
A CNAME at the apex breaks the rest of the zone (MX, TXT, NS, etc.). Use ALIAS / ANAME / flattening at apex. Also: never CNAME a host that itself has MX or NS records.