Custom domains in Supabase - Time & Space Complexity

Time Complexity: Custom domains

O(n)

Understanding Time Complexity

When setting up custom domains in Supabase, it's important to understand how the time to complete the setup grows as you add more domains.

We want to know how the number of domains affects the total operations needed to configure them.

Scenario Under Consideration

Analyze the time complexity of adding multiple custom domains to a Supabase project.

// Example: Adding multiple custom domains
const domains = ['example1.com', 'example2.com', 'example3.com'];
for (const domain of domains) {
  await supabase.functions.createCustomDomain({
    domain: domain,
    projectId: 'project-id'
  });
}
    

This code adds each domain one by one to the Supabase project by calling the API for each domain.

Identify Repeating Operations

Identify the API calls, resource provisioning, data transfers that repeat.

• Primary operation: API call to create a custom domain for each domain.
• How many times: Once per domain added.

How Execution Grows With Input

Each new domain requires one API call, so the total calls grow directly with the number of domains.

Input Size (n)	Approx. API Calls/Operations
10	10 API calls
100	100 API calls
1000	1000 API calls

Pattern observation: The number of operations grows in a straight line as you add more domains.

Final Time Complexity

Time Complexity: O(n)

This means the time to add custom domains grows directly in proportion to how many domains you add.

Common Mistake

[X] Wrong: "Adding multiple domains happens all at once, so time stays the same no matter how many domains."

[OK] Correct: Each domain requires a separate API call, so the total time increases with each additional domain.

Interview Connect

Understanding how operations scale with input size helps you design efficient cloud setups and explain your reasoning clearly in interviews.

Self-Check

"What if the API allowed batch adding of multiple domains in one call? How would the time complexity change?"

Practice

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

easy

A. To enable faster query execution

B. To increase database storage capacity

C. To create multiple user accounts automatically

D. To use your own website address instead of a default Supabase URL

Solution

1. Step 1: Understand what a custom domain is

   A custom domain lets you use your own website address instead of a generic one provided by a service.

2. Step 2: Relate to Supabase usage

   In Supabase, setting a custom domain means your app uses your own URL, making it look professional and branded.

3. Final Answer:

   To use your own website address instead of a default Supabase URL -> Option D

4. Quick Check:

   Custom domain = Own website address [OK]

Hint: Custom domain means your own website address [OK]

Common Mistakes:

• Thinking it increases database size
• Confusing with performance features
• Assuming it creates user accounts

2. Which DNS record type must you add to point your custom domain to Supabase?

easy

A. CNAME record

B. MX record

C. TXT record

D. SRV record

Solution

1. Step 1: Identify DNS record types for domain pointing

   CNAME records are used to alias one domain name to another, commonly used to point custom domains to services.

2. Step 2: Match with Supabase custom domain setup

   Supabase requires a CNAME record to link your custom domain to their servers.

3. Final Answer:

   CNAME record -> Option A

4. Quick Check:

   Custom domain pointing uses CNAME [OK]

Hint: Use CNAME to point domain to Supabase [OK]

Common Mistakes:

• Using MX record which is for email
• Using TXT record meant for verification
• Confusing SRV record with domain pointing

3. Given this Supabase custom domain setup snippet:

domain: "app.example.com"
records: [
  { type: "CNAME", value: "db.supabase.co" }
]

What happens when a user visits app.example.com?

medium

A. They are redirected to the Supabase database interface

B. Their browser connects to Supabase hosting for the app

C. They get an email verification prompt

D. They see a DNS error because CNAME is incorrect

Solution

1. Step 1: Understand CNAME effect

   The CNAME record points the domain to Supabase's hosting address, so requests go there.

2. Step 2: Interpret user visit behavior

   When visiting app.example.com, the browser connects to Supabase hosting serving the app, not the database interface or errors.

3. Final Answer:

   Their browser connects to Supabase hosting for the app -> Option B

4. Quick Check:

   CNAME directs browser to Supabase hosting [OK]

Hint: CNAME points domain to hosting, not email or errors [OK]

Common Mistakes:

• Confusing database interface with hosting
• Assuming DNS error from correct CNAME
• Thinking email verification appears on visit

4. You set a custom domain in Supabase but get a security warning in browsers. What is the most likely cause?

medium

A. You did not add an MX record

B. You used an invalid domain name format

C. You forgot to enable SSL for the custom domain

D. You set the CNAME to the wrong IP address

Solution

1. Step 1: Identify cause of browser security warnings

   Security warnings usually happen when SSL (secure connection) is missing or invalid.

2. Step 2: Relate to Supabase custom domain setup

   Supabase requires enabling SSL for custom domains to avoid browser warnings.

3. Final Answer:

   You forgot to enable SSL for the custom domain -> Option C

4. Quick Check:

   Missing SSL causes browser security warnings [OK]

Hint: Always enable SSL for custom domains [OK]

Common Mistakes:

• Confusing MX record with SSL
• Thinking domain format causes security warning
• Assuming CNAME IP address is used instead of hostname

5. You want to set up a custom domain dashboard.myapp.com for your Supabase project. Which steps must you follow to ensure it works correctly and securely?

hard

A. Buy the domain, add a CNAME DNS record pointing to Supabase, then enable SSL in Supabase settings

B. Buy the domain, add an MX record pointing to Supabase, then enable SSL in Supabase settings

C. Buy the domain, add a TXT record for verification, then disable SSL to avoid errors

D. Buy the domain, add an A record pointing to Supabase IP, then skip SSL setup

Solution

1. Step 1: Purchase domain and configure DNS

   First, buy your domain (dashboard.myapp.com) and add a CNAME record pointing to Supabase's domain to route traffic correctly.

2. Step 2: Enable SSL for secure connections

   Then, enable SSL in Supabase settings to secure the connection and avoid browser warnings.

3. Final Answer:

   Buy the domain, add a CNAME DNS record pointing to Supabase, then enable SSL in Supabase settings -> Option A

4. Quick Check:

   Domain + CNAME + SSL = Correct setup [OK]

Hint: Domain + CNAME + SSL = working custom domain [OK]

Common Mistakes:

• Using MX or TXT records incorrectly
• Skipping SSL causing security warnings
• Using A record instead of CNAME for Supabase