Custom domains in Deno - Step-by-Step Execution

Concept Flow - Custom domains

Start Deno Deploy

↓

Configure Custom Domain

↓

Verify Domain Ownership

↓

Update DNS Records

↓

Deno Deploy Routes Traffic

↓

User Accesses Custom Domain

↓

Serve Content from Deno Deploy

This flow shows how you set up a custom domain in Deno Deploy, verify it, update DNS, and serve your app through that domain.

Execution Sample

Deno

import { serve } from "https://deno.land/std/http/server.ts";

serve(() => new Response("Hello from custom domain!"));

A simple Deno server that responds with a greeting, ready to be linked to a custom domain.

Execution Table

Step	Action	Result	Notes
1	Start Deno Deploy project	Project created	Ready to add custom domain
2	Add custom domain in Deno Deploy dashboard	Domain added, pending verification	Domain name entered
3	Verify domain ownership	Verification instructions shown	Usually DNS TXT record
4	Update DNS records at domain registrar	DNS records updated	TXT and CNAME records set
5	Deno Deploy verifies DNS changes	Domain verified	Verification successful
6	Deno Deploy routes traffic from custom domain	Traffic routed	Custom domain active
7	User visits custom domain URL	Content served	Response: 'Hello from custom domain!'

💡 Process ends when custom domain is verified and serving content successfully.

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 5	Final
customDomainStatus	Not set	Pending verification	DNS updated	Verified	Active
dnsRecords	Empty	Empty	TXT and CNAME added	Propagated	Stable

Key Moments - 3 Insights

Why does the custom domain show 'pending verification' after adding it?

Because Deno Deploy needs you to prove ownership by updating DNS records, as shown in execution_table step 3 and 4.

What happens if DNS records are not updated correctly?

Deno Deploy cannot verify the domain, so the status stays 'pending verification' and traffic won't route, as seen in step 5.

When does the user see the content served from the custom domain?

Only after verification and routing are complete, at step 7 in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the customDomainStatus after Step 4?

A Verified

B DNS updated

C Pending verification

D Active

💡 Hint

Check variable_tracker row for customDomainStatus after Step 4.

At which step does Deno Deploy confirm the domain ownership?

A Step 3

B Step 6

C Step 5

D Step 7

💡 Hint

Look at execution_table where verification is successful.

If DNS records are not updated, what will be the final customDomainStatus?

A Pending verification

B Active

C Verified

D DNS updated

💡 Hint

Refer to key_moments explanation about DNS update importance.

Concept Snapshot

Custom domains in Deno Deploy:
1. Add your domain in the dashboard.
2. Verify ownership by updating DNS records.
3. Wait for verification to complete.
4. Traffic routes through your domain.
5. Your app serves content at the custom domain URL.

Full Transcript

This visual execution shows how to set up a custom domain in Deno Deploy. First, you create your project and add the domain in the dashboard. Then, you verify ownership by adding DNS records at your domain registrar. Once Deno Deploy confirms the DNS changes, the domain status changes to verified and active. Finally, users can access your app through the custom domain, and your server responds with content. The variable tracker shows the domain status and DNS records state at each step. Key moments clarify why verification is needed and when content is served. The quiz tests understanding of these steps and states.

Practice

1. What is the main purpose of setting a custom domain in a Deno server?

easy

A. To increase the server's processing speed

B. To use your own website name instead of a generic address

C. To automatically update the server software

D. To enable debugging features in Deno

Solution

1. Step 1: Understand what a custom domain is

   A custom domain lets you use a personalized website name instead of a default or generic address.

2. Step 2: Identify the purpose in Deno context

   Setting a custom domain in Deno allows your server to respond to your own website name, making it easier for users to find your site.

3. Final Answer:

   To use your own website name instead of a generic address -> Option B

4. Quick Check:

   Custom domain = personalized website name [OK]

Hint: Custom domain means your own website name, not generic [OK]

Common Mistakes:

• Confusing custom domain with server speed
• Thinking it updates software automatically
• Assuming it enables debugging

2. Which of the following is the correct way to set a custom domain hostname in Deno's serve function?

easy

A. serve({ url: "mydomain.com" })

B. serve({ domain: "mydomain.com" })

C. serve({ hostname: "mydomain.com" })

D. serve({ host: "mydomain.com" })

Solution

1. Step 1: Recall Deno serve options

   The serve function accepts an option called hostname to set the domain name.

2. Step 2: Match the correct option key

   Only hostname is the correct key; others like domain, host, or url are invalid here.

3. Final Answer:

   serve({ hostname: "mydomain.com" }) -> Option C

4. Quick Check:

   Use hostname option in serve [OK]

Hint: Use 'hostname' option exactly in serve function [OK]

Common Mistakes:

• Using 'domain' or 'host' instead of 'hostname'
• Passing the domain as a string without key
• Confusing 'url' with hostname option

3. Given the following code snippet, what will be the hostname the server listens on?

import { serve } from "https://deno.land/std/http/server.ts";
serve(() => new Response("Hello"), { hostname: "example.com" });

medium

A. The server will throw a runtime error

B. The server listens on localhost only

C. The server listens on all IP addresses

D. The server listens on example.com domain

Solution

1. Step 1: Examine the hostname option

   The code sets hostname: "example.com" in the serve options.

2. Step 2: Understand hostname resolution and binding

   Deno resolves "example.com" to a public IP (93.184.216.34) via DNS. If the IP is assigned to the local machine's network interfaces, the server binds successfully and listens on that domain. Otherwise, it will throw a runtime error.

3. Step 3: Typical behavior

   Usually, binding to a hostname that resolves to a public IP not assigned locally will fail. But if the environment is configured properly (e.g., hosts file or network interface), it can succeed.

4. Final Answer:

   The server listens on example.com domain -> Option D

5. Quick Check:

   Hostname option sets server listening domain [OK]

Hint: Hostname option sets server listening domain [OK]

Common Mistakes:

• Thinking server listens directly on domain without IP resolution
• Assuming default localhost behavior
• Believing it falls back to all IPs

4. You set hostname: "mydomain.com" in your Deno server but users cannot reach your site. What is the most likely cause?

medium

A. You forgot to point your domain's DNS to your server's IP address

B. The serve function does not support custom domains

C. You must use host instead of hostname

D. Deno requires a special flag to enable custom domains

Solution

1. Step 1: Verify Deno serve supports hostname

   Deno's serve supports hostname option, so options B, C, and D are incorrect.

2. Step 2: Check DNS setup

   If users cannot reach the site, the domain's DNS likely does not point to the server's IP, blocking access.

3. Final Answer:

   You forgot to point your domain's DNS to your server's IP address -> Option A

4. Quick Check:

   DNS must point domain to server IP [OK]

Hint: Check DNS points domain to server IP if unreachable [OK]

Common Mistakes:

• Assuming serve lacks custom domain support
• Using wrong option key like 'host'
• Thinking Deno needs special flags for domains

5. You want to serve your Deno app on your custom domain "myapp.com" and also allow access via localhost for testing. Which setup correctly supports both?

hard

A. Set hostname to "0.0.0.0" to listen on all interfaces including domain and localhost

B. Set hostname to "myapp.com, localhost" in a single serve call

C. Run two servers: one with hostname "myapp.com" and one with hostname "localhost"

D. Use hostname "localhost" and rely on DNS to redirect "myapp.com"

Solution

1. Step 1: Understand hostname options

   Setting hostname to "0.0.0.0" makes the server listen on all network interfaces, including your domain and localhost.

2. Step 2: Evaluate other options

   Run two servers: one with hostname "myapp.com" and one with hostname "localhost" requires two servers which is inefficient; Set hostname to "myapp.com, localhost" in a single serve call is invalid syntax; Use hostname "localhost" and rely on DNS to redirect "myapp.com" relies on DNS redirect which does not work for localhost access.

3. Final Answer:

   Set hostname to "0.0.0.0" to listen on all interfaces including domain and localhost -> Option A

4. Quick Check:

   Use 0.0.0.0 to listen on all interfaces [OK]

Hint: Use 0.0.0.0 hostname to serve domain and localhost [OK]

Common Mistakes:

• Trying to list multiple hostnames in one serve call
• Running multiple servers unnecessarily
• Relying on DNS to redirect localhost