Purging CDN cache in Azure - Step-by-Step Execution

Process Flow - Purging CDN cache

Request to purge cache

↓

Authenticate request

↓

Identify CDN endpoint

↓

Send purge command

↓

CDN invalidates cached content

↓

Confirm purge success

↓

Serve fresh content on next request

The purge process starts with a request, authenticates it, targets the CDN endpoint, sends the purge command, invalidates cached content, confirms success, and then serves fresh content.

Execution Sample

Azure

az cdn endpoint purge --resource-group MyResourceGroup --profile-name MyProfile --name MyEndpoint --content-paths '/images/*'

This command purges cached content under '/images/*' from the specified Azure CDN endpoint.

Process Table

Step	Action	Input/Parameter	System Response	Result
1	Receive purge request	ResourceGroup=MyResourceGroup, Profile=MyProfile, Endpoint=MyEndpoint, Paths='/images/*'	Request accepted	Proceed to authentication
2	Authenticate request	User credentials or token	Authentication successful	Proceed to identify endpoint
3	Identify CDN endpoint	MyEndpoint under MyProfile	Endpoint found	Ready to send purge command
4	Send purge command	Paths='/images/*'	Purge command sent to CDN	Cache invalidation started
5	CDN invalidates cache	Paths='/images/*'	Cache entries removed	Content will be refreshed on next request
6	Confirm purge success	System status	Purge completed successfully	End process
7	Serve fresh content	Next user request	Fetches fresh content from origin	User receives updated content

💡 Purge completes after cache invalidation and confirmation, ensuring fresh content delivery.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	Final
Request Status	None	Received	Authenticated	Endpoint Identified	Purge Command Sent	Cache Invalidated	Purge Confirmed	Completed
Cache State	Cached content present	Cached content present	Cached content present	Cached content present	Invalidation in progress	Cache cleared for '/images/*'	Cache cleared	Fresh content served

Key Moments - 3 Insights

Why does the purge command target specific content paths like '/images/*' instead of the whole cache?

Targeting specific paths limits the purge scope, making it faster and less disruptive. See execution_table row 4 where the purge command is sent only for '/images/*'.

What happens if authentication fails during the purge request?

The process stops at step 2 in the execution_table because the request is not authorized, so no cache invalidation occurs.

Does purging immediately update content for all users?

No, purging invalidates cached content so that on the next user request (step 7), fresh content is fetched from the origin server.

Visual Quiz - 3 Questions

Look at the execution_table, what is the system response at step 3?

A Authentication successful

B Endpoint found

C Purge command sent to CDN

D Cache entries removed

💡 Hint

Check the 'System Response' column for step 3 in the execution_table.

At which step does the cache actually get cleared for the specified paths?

A Step 4

B Step 5

C Step 6

D Step 7

💡 Hint

Look for 'Cache entries removed' in the 'System Response' column.

If the purge command targeted the whole cache instead of '/images/*', how would the variable 'Cache State' change after step 5?

A Only '/images/*' cache cleared

B No change in cache state

C Entire cache cleared

D Cache state becomes invalid

💡 Hint

Refer to variable_tracker row 'Cache State' after step 5 and imagine the scope change.

Concept Snapshot

Purging CDN cache removes outdated content from the CDN.
Use Azure CLI command 'az cdn endpoint purge' with resource group, profile, endpoint, and content paths.
Authentication is required before purging.
Only specified paths are purged to limit impact.
After purge, fresh content is served on next request.

Full Transcript

Purging CDN cache in Azure involves sending a purge request specifying the resource group, CDN profile, endpoint, and content paths to clear. The system authenticates the request, identifies the CDN endpoint, and sends the purge command. The CDN then invalidates the cached content for the specified paths. Once the purge is confirmed, the next user request fetches fresh content from the origin server. This process ensures users receive updated content without waiting for cache expiration.

Practice

1. What is the main purpose of purging a CDN cache in Azure?

easy

A. To increase the storage capacity of the CDN

B. To remove outdated content so users get the latest version

C. To add new content to the CDN cache

D. To monitor traffic statistics on the CDN

Solution

1. Step 1: Understand CDN cache role

   CDN caches store copies of content to serve users faster.

2. Step 2: Purpose of purging cache

   Purging removes old cached content so fresh content is served.

3. Final Answer:

   To remove outdated content so users get the latest version -> Option B

4. Quick Check:

   Purging = Remove outdated content [OK]

Hint: Purging means clearing old cache to refresh content [OK]

Common Mistakes:

• Thinking purging adds content instead of removing
• Confusing purging with monitoring or scaling
• Believing purging increases storage capacity

2. Which Azure CLI command correctly purges the CDN cache for a specific content path?

easy

A. az cdn endpoint purge --resource-group MyGroup --profile-name MyProfile --name MyEndpoint --content-paths '/images/*'

B. az cdn endpoint create --resource-group MyGroup --profile-name MyProfile --name MyEndpoint --content-paths '/images/*'

C. az cdn endpoint start --resource-group MyGroup --profile-name MyProfile --name MyEndpoint --content-paths '/images/*'

D. az cdn profile purge --resource-group MyGroup --name MyProfile --content-paths '/images/*'

Solution

1. Step 1: Identify correct command for purging

   The command to purge cache is az cdn endpoint purge.

2. Step 2: Check parameters

   It requires resource group, profile name, endpoint name, and content paths.

3. Final Answer:

   az cdn endpoint purge --resource-group MyGroup --profile-name MyProfile --name MyEndpoint --content-paths '/images/*' -> Option A

4. Quick Check:

   Purging uses az cdn endpoint purge [OK]

Hint: Purge command uses 'endpoint purge' with content paths [OK]

Common Mistakes:

• Using 'create' or 'start' commands instead of 'purge'
• Confusing profile purge with endpoint purge
• Omitting required parameters like endpoint name

3. Given this Azure CLI command:
az cdn endpoint purge --resource-group RG1 --profile-name Profile1 --name Endpoint1 --content-paths '/css/*' '/js/app.js'
What will happen after running it?

medium

A. The command will fail due to incorrect syntax

B. Only the '/css/*' files will be purged from the CDN cache

C. Both '/css/*' and '/js/app.js' files will be purged from the CDN cache

D. Only '/js/app.js' will be purged, '/css/*' will be ignored

Solution

1. Step 1: Analyze content-paths parameter

   The command lists two paths: '/css/*' and '/js/app.js'. Both are valid and separated by space.

2. Step 2: Understand purge effect

   Both specified paths will be purged from the CDN cache after command runs.

3. Final Answer:

   Both '/css/*' and '/js/app.js' files will be purged from the CDN cache -> Option C

4. Quick Check:

   Multiple paths purge all listed [OK]

Hint: Multiple content paths purge all specified files [OK]

Common Mistakes:

• Assuming only first path is purged
• Thinking command syntax is invalid with multiple paths
• Believing wildcard and file path cannot be combined

4. You run this command to purge CDN cache:
az cdn endpoint purge --resource-group RG1 --profile-name Profile1 --name Endpoint1 --content-paths '/images/logo.png'
But the cache is not cleared. What is the most likely cause?

medium

A. The content path is incorrect or does not match cached files

B. The resource group name is misspelled

C. The Azure CLI command does not support purging images

D. The CDN endpoint is not created yet

Solution

1. Step 1: Check command correctness

   The command syntax is correct and supports purging images.

2. Step 2: Identify common purge failure reason

   If cache is not cleared, often the content path does not match cached files exactly.

3. Final Answer:

   The content path is incorrect or does not match cached files -> Option A

4. Quick Check:

   Incorrect path = purge fails [OK]

Hint: Verify content path matches cached files exactly [OK]

Common Mistakes:

• Assuming CLI cannot purge images
• Ignoring typos in resource group or endpoint names
• Thinking purge works instantly without matching paths

5. You manage a global website using Azure CDN. You want to purge cache for a frequently updated JavaScript file but minimize performance impact. Which strategy is best?

hard

A. Disable CDN caching for all files to avoid purging

B. Purge the entire CDN endpoint cache every hour

C. Purge cache only once a month to reduce load

D. Purge only the specific JavaScript file path instead of the entire CDN endpoint

Solution

1. Step 1: Understand impact of purging scope

   Purging entire endpoint cache causes high load and delays for all users.

2. Step 2: Choose targeted purging

   Purging only the specific JavaScript file updates that content with minimal performance impact.

3. Final Answer:

   Purge only the specific JavaScript file path instead of the entire CDN endpoint -> Option D

4. Quick Check:

   Targeted purge = minimal impact [OK]

Hint: Purge specific files, not whole endpoint, to save performance [OK]

Common Mistakes:

• Purging entire cache too often causing slowdowns
• Disabling caching loses CDN benefits
• Purging too rarely causing stale content