# Exercise 1: Design the DNS Records for a Multi-Service Company Domain

## Scenario

You're setting up DNS for `northwind.dev`, a company launching:

- A marketing site at the bare domain, `northwind.dev`, and also reachable as `www.northwind.dev`.
- A product web app at `app.northwind.dev`.
- A public API at `api.northwind.dev`, fronted by a load balancer with two IPs for redundancy: `203.0.113.10` and `203.0.113.11`.
- Static assets (images, JS bundles) served from a CDN at `cdn.northwind.dev` — the CDN provider tells you to point this at `edge.cdnprovider.net`.
- Company email handled by a third-party provider, which requires an MX record pointing at `mail.provider.net` (priority 10) and a TXT record for SPF: `v=spf1 include:_spf.provider.net ~all`.
- A domain-ownership verification TXT record required by the CDN provider before it will issue a TLS certificate: `provider-verification=abc123xyz`.

The company is launching in one week and does not expect to change any of these IPs or providers for at least six months afterward.

## Deliverables

Produce all of the following, in this file, below this line:

1. **A full record table** — columns: Name | Type | Value | TTL (seconds) | Notes. One row per record needed to satisfy every requirement above (the bare domain and `www.northwind.dev` may need different record types — explain why in the Notes column, referencing theory section 3's `CNAME` restriction).
2. **A TTL justification** — for each *distinct* TTL value you chose, explain why that value fits this domain's stated change frequency (theory section 5), and why a single company-wide TTL wouldn't be the right call here.
3. **A one-paragraph explanation of what happens, step by step, the first time a new visitor's browser resolves `api.northwind.dev`** — walk the full resolution chain from theory section 4, naming every layer involved.
4. **A one-paragraph explanation of why `cdn.northwind.dev` is a `CNAME` to the provider's domain instead of the company hard-coding the CDN's current IP as an `A` record** — connect this to theory section 6's discussion of who controls the DNS answer for CDN-fronted names.

## Constraints

- Every record's Name/Type/Value must be internally consistent with the scenario (no invented IPs beyond the ones given; the CDN and mail provider hostnames must be used exactly as given).
- The bare `northwind.dev` domain must not violate the `CNAME`-coexistence rule from theory section 3, given that it also needs MX and TXT records.
- Do not propose GeoDNS or round-robin beyond what's needed to represent the API's two given IPs.