CDN with custom domains in Azure - Time & Space Complexity

Time Complexity: CDN with custom domains

O(n)

Understanding Time Complexity

When setting up a CDN with custom domains in Azure, it is important to understand how the time to configure and deploy grows as you add more custom domains.

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

Scenario Under Consideration

Analyze the time complexity of the following operation sequence.

// Create a CDN profile
az cdn profile create --name MyCDNProfile --resource-group MyResourceGroup --location eastus

// Create a CDN endpoint
az cdn endpoint create --name MyCDNEndpoint --profile-name MyCDNProfile --resource-group MyResourceGroup --origin www.example.com

// For each custom domain, add it to the CDN endpoint
foreach domain in customDomains:
  az cdn custom-domain create --endpoint-name MyCDNEndpoint --profile-name MyCDNProfile --resource-group MyResourceGroup --hostname domain

This sequence creates a CDN profile and endpoint, then adds multiple custom domains to the endpoint.

Identify Repeating Operations

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

• Primary operation: Adding each custom domain to the CDN endpoint via the az cdn custom-domain create command.
• How many times: Once for each custom domain you want to add.

How Execution Grows With Input

Each custom domain requires a separate API call to add it to the CDN endpoint. So, as you add more domains, the total number of calls grows directly with the number of domains.

Input Size (n)	Approx. Api Calls/Operations
10	10 calls to add custom domains
100	100 calls to add custom domains
1000	1000 calls to add custom domains

Pattern observation: The number of operations grows linearly as you add more custom 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 custom domains is a single operation regardless of how many domains there are."

[OK] Correct: Each custom domain requires its own API call and configuration step, so the total time grows with the number of domains.

Interview Connect

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

Self-Check

What if we batch multiple custom domains in a single API call? How would the time complexity change?

Practice

1. What is the primary purpose of using a custom domain with Azure CDN?

easy

A. To deliver content using your own website address instead of the default CDN URL

B. To increase the storage capacity of the CDN

C. To reduce the cost of CDN services

D. To disable HTTPS on the CDN endpoint

Solution

1. Step 1: Understand CDN default behavior

   Azure CDN provides a default URL for content delivery, but it uses a generic domain name.

2. Step 2: Purpose of custom domain

   Using a custom domain lets you serve content with your own website address, improving branding and user trust.

3. Final Answer:

   To deliver content using your own website address instead of the default CDN URL -> Option A

4. Quick Check:

   Custom domain = Own website address [OK]

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

Common Mistakes:

• Thinking custom domain increases storage
• Assuming custom domain reduces cost
• Believing custom domain disables HTTPS

2. Which DNS record type must you create to map your custom domain to an Azure CDN endpoint?

easy

A. CNAME record

B. SRV record

C. TXT record

D. MX record

Solution

1. Step 1: Identify DNS record for domain aliasing

   CNAME records map one domain name to another, which is needed to point your custom domain to the CDN endpoint.

2. Step 2: Exclude other DNS record types

   MX is for mail, TXT for text info, SRV for service location, none suitable for domain aliasing.

3. Final Answer:

   CNAME record -> Option A

4. Quick Check:

   Custom domain uses CNAME DNS record [OK]

Hint: Custom domain points to CDN via CNAME record [OK]

Common Mistakes:

• Using MX record for domain mapping
• Confusing TXT record with CNAME
• Trying to use SRV record for CDN

3. Given the following Azure CLI command snippet to add a custom domain to a CDN endpoint, what will happen if the DNS CNAME record is not set correctly?

az cdn custom-domain create --endpoint-name myEndpoint --profile-name myProfile --resource-group myGroup --hostname www.example.com

medium

A. The custom domain will be added successfully without any issues

B. The CDN endpoint will automatically create the DNS record

C. The custom domain will be added but HTTPS will be disabled

D. The command will fail with a DNS validation error

Solution

1. Step 1: Understand DNS validation in Azure CDN

   Azure CDN requires DNS validation to confirm ownership of the custom domain via CNAME record.

2. Step 2: Effect of missing or incorrect DNS record

   If the CNAME record is missing or incorrect, the command fails with a DNS validation error to prevent misconfiguration.

3. Final Answer:

   The command will fail with a DNS validation error -> Option D

4. Quick Check:

   Missing CNAME causes DNS validation error [OK]

Hint: DNS must validate custom domain or command fails [OK]

Common Mistakes:

• Assuming CDN auto-creates DNS records
• Thinking custom domain adds without DNS setup
• Believing HTTPS disables if DNS is wrong

4. You added a custom domain to your Azure CDN endpoint but HTTPS is not working. Which of the following is the most likely cause?

medium

A. The CDN endpoint does not support HTTPS at all

B. You used an A record instead of a CNAME record in DNS

C. You forgot to enable HTTPS on the custom domain in the CDN settings

D. The CDN profile is in a different Azure region than your resource group

Solution

1. Step 1: Check HTTPS enablement for custom domain

   Azure CDN requires explicit enabling of HTTPS on custom domains to serve secure content.

2. Step 2: Exclude other causes

   CDN endpoints support HTTPS, A record usage causes DNS issues but not HTTPS directly, region mismatch does not block HTTPS.

3. Final Answer:

   You forgot to enable HTTPS on the custom domain in the CDN settings -> Option C

4. Quick Check:

   HTTPS must be enabled on custom domain [OK]

Hint: Enable HTTPS explicitly for custom domain [OK]

Common Mistakes:

• Assuming HTTPS is automatic
• Blaming region mismatch for HTTPS failure
• Using A record instead of CNAME but ignoring HTTPS setting

5. You want to design a scalable Azure CDN solution with a custom domain that supports HTTPS and handles millions of users globally. Which combination of steps is the best practice?

hard

A. Create a CDN profile only, add your custom domain with an A record, disable HTTPS to reduce latency, and rely on a single CDN POP

B. Create a CDN profile and endpoint, add your custom domain with a CNAME DNS record, enable HTTPS with Azure-managed certificates, and use multiple CDN POPs worldwide

C. Create multiple CDN profiles for each region, add custom domains without DNS changes, and enable HTTPS manually with self-signed certificates

D. Use Azure CDN without custom domains, enable HTTPS, and configure DNS to point directly to the origin server

Solution

1. Step 1: Setup CDN profile and endpoint with custom domain

   Create a CDN profile and endpoint, then add your custom domain using a CNAME DNS record for proper domain mapping.

2. Step 2: Enable HTTPS and use global CDN POPs

   Enable HTTPS using Azure-managed certificates for security and scalability, and leverage multiple CDN Points of Presence (POPs) worldwide to handle global traffic efficiently.

3. Final Answer:

   Create a CDN profile and endpoint, add your custom domain with a CNAME DNS record, enable HTTPS with Azure-managed certificates, and use multiple CDN POPs worldwide -> Option B

4. Quick Check:

   Custom domain + CNAME + HTTPS + global POPs = Best practice [OK]

Hint: Use CNAME, enable HTTPS, and leverage global CDN POPs [OK]

Common Mistakes:

• Using A record instead of CNAME
• Disabling HTTPS to save latency
• Skipping DNS changes for custom domains
• Relying on single CDN POP for global scale