How to purge the CDN cache

Learn how to purge or remove the cached HTTP response from the AEM as a Cloud Service’s CDN. Using the self-service feature called Purge API Token, you can purge the cache for a specific resource, a group of resources, and the entire cache.

In this tutorial, you learn how to set up and use the Purge API Token to purge the CDN cache of the sample AEM WKND site using the self-service feature.

Cache invalidation vs explicit purge

There are two ways to remove the cached resources from the CDN:

When cached resources are removed from the CDN cache, the next request for the same resource fetches the latest version from the origin server.

Set up the Purge API Token

Let’s learn how to set up the Purge API Token to purge the CDN cache.

Configure the CDN rule

The Purge API Token is created by configuring the CDN rule in your AEM project code.

kind: "CDN"
version: "1"
metadata:
  envTypes: ["dev", "stage", "prod"]
data:
  authentication: # The main authentication configuration
    authenticators: # The list of authenticators
       - name: purge-auth # The name of the authenticator
         type: purge  # The type of the authenticator, must be purge
         purgeKey1: ${{CDN_PURGEKEY_081324}} # The first purge key, must be referenced by the Cloud Manager secret-type environment variable name ${{CDN_EDGEKEY_073124}}
         purgeKey2: ${{CDN_PURGEKEY_111324}} # The second purge key, must be referenced by the Cloud Manager secret-type environment variable name ${{CDN_EDGEKEY_111324}}. It is used for the rotation of secrets without any interruptions.
    rules: # The list of authentication rules
       - name: purge-auth-rule # The name of the rule
         when: { reqProperty: tier, equals: "publish" } # The condition when the rule should be applied
         action: # The action to be taken when the rule is applied
           type: authenticate # The type of the action, must be authenticate
           authenticator: purge-auth # The name of the authenticator to be used, must match the name from the above authenticators list

In above rule, both purgeKey1 and purgeKey2 are added from the beginning to support the rotation of secrets without any interruptions. However, you can start with only purgeKey1 and add purgeKey2 later when rotating the secrets.

Create Cloud Manager environment variable

Next, create the Cloud Manager environment variables to store the Purge API Token value.

Deploy the CDN rule

Finally, deploy the configured CDN rule to the AEM as a Cloud Service environment using the Cloud Manager pipeline.

Use the Purge API Token

To purge the CDN cache, invoke the AEM service specific domain URL with the Purge API Token. The syntax to purge the cache is as follows:

PURGE <URL> HTTP/1.1
Host: <AEM_SERVICE_SPECIFIC_DOMAIN>
X-AEM-Purge-Key: <PURGE_API_TOKEN>
X-AEM-Purge: <PURGE_TYPE>
Surrogate-Key: <SURROGATE_KEY>

Where:

Purge the cache for a specific resource

In this example, the curl command purges the cache for the /us/en.html resource on the WKND site deployed in an AEM as a Cloud Service environment.

curl -X PURGE "https://publish-p46652-e1315806.adobeaemcloud.com/us/en.html" \
-H "X-AEM-Purge-Key: 123456789" \
-H "X-AEM-Purge: hard"

Upon successful purge, a 200 OK response is returned with JSON content.

{ "status": "ok", "id": "1000098-1722961031-13237063" }

Purge the cache for a group of resources

In this example, the curl command purges the cache for the group of resources with the surrogate key wknd-assets. The Surrogate-Key response header is set in wknd.vhost, for example:

<VirtualHost *:80>
    ...

    # Core Component Image Component: long-term caching (30 days) for immutable URLs, background refresh to avoid MISS
    <LocationMatch "^/content/.*\.coreimg.*\.(?i:jpe?g|png|gif|svg)$">
        Header set Cache-Control "max-age=2592000,stale-while-revalidate=43200,stale-if-error=43200,public,immutable" "expr=%{REQUEST_STATUS} < 400"
        # Set Surrogate-Key header to group the cache of WKND assets, thus it can be flushed independtly
        Header set Surrogate-Key "wknd-assets"
        Header set Age 0
    </LocationMatch>

    ...
</VirtualHost>

curl -X PURGE "https://publish-p46652-e1315806.adobeaemcloud.com" \
-H "Surrogate-Key: wknd-assets" \
-H "X-AEM-Purge-Key: 123456789" \
-H "X-AEM-Purge: hard"

Upon successful purge, a 200 OK response is returned with JSON content.

{ "wknd-assets": "10027-1723478994-2597809-1" }

Purge the entire cache

In this example, using the curl command the entire cache is purged from the sample WKND site deployed on AEM as a Cloud Service environment.

curl -X PURGE "https://publish-p46652-e1315806.adobeaemcloud.com/" \
-H "X-AEM-Purge-Key: 123456789" \
-H "X-AEM-Purge: all"

Upon successful purge, a 200 OK response is returned with JSON content.

{"status":"ok"}

Verify the cache purge

To verify the cache purge, access the resource URL in the web browser and review the response headers. The X-Cache header value should be MISS.