Update BYOD docs: clarify DNS options and staging workflows

[Copilot]

Users were unclear about DNS management options when using custom domains, particularly around avoiding repeated defang cert gen calls for staging environments and the difference between using Route 53 vs external DNS providers.

Changes

docs/concepts/domains.mdx

• Restructured BYOD section with two DNS management options:
  • Option 1: External DNS (CloudFlare, Namecheap) with direct domain or CNAME approaches
  • Option 2: Route 53 (automatic DNS/cert management, no cert gen needed)
• Documented both domain formats provided on deployment: defang.app and cloud provider (e.g., AWS ELB)
• Added guidance on using --project-name for environment separation

docs/tutorials/use-your-own-domain-name.mdx

• Split into two approaches: Route 53 (recommended) vs external DNS providers

• Added CNAME workflow for staging environments that frequently deploy/teardown without DNS reconfiguration:

  services:
      web:
          # No domainname - use defang.app domain
          ports:
          - mode: ingress
            target: 3000
            protocol: http

  Then CNAME staging.example.com → web--3000.myproject.user.defang.app once. Subsequent deployments work without DNS changes.

• Added multi-environment management section with name: field and --project-name flag examples

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update BYOD docs</issue_title>
<issue_description>Update the BYOD docs to reflect the questions and answers from this dialog:

you once mentioned that if i used route 53 to maintain my domain's dns I would not need to change configurations on my cloudflare everytime i needed to a defang cert gen. do you have a tutorial on how i should set it up? or is it auto-setup if i move my domain management to the same aws account?

I have my domain in namecheap, and the DNS is at cloudflare, i could move it to aws if that will make the up and down easier without having tio reconfigure, Particularly because i want to set up a staging environment that I will keep putting down to save costs when i dont need it and put it up when i have to run a demo..... would hate to have to change a cname entry everytime i put it up....

well, you can always have your subdomains be a CNAME to the xyz.defang.app domain.. defang stack will make that easier.
But you can already do that using custom project names, either setting different name: in compose files, or by passing --project-name
(our new stack feature will basically do this for you, and it becomes your project-name suffix, eg. project "hello" and stack "Staging" would deploy as "hello-staging")

If you use the defang.app as CNAMEs , you wouldn't have to do anything. You'd still have do defang cert gen to recreate SSL certs after up.
THAT's the part you can skip if you move the DNS to Route53

does it give it to me when i defang up, i have never noticed it, i have always noticed something like this: defang-xyz-b0f79bb-123456789012.ca-central-1.elb.amazonaws.com

It does both! Typically people want to use the amazon one, because then you're not dependent on Defang

Perfect, then i can configure it to project name and it would work perfectly..... :)

The defang one will always be ...defang.app, or even --… if you have more ports on a service
</issue_description>

<agent_instructions>Update the BYOD docs to reflect the answers in this dialog.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Update BYOD docs #325

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