Edge Security Acceleration:Purge cache by tag

Features

The tag-based cache purge feature simplifies bulk purging of related cached resources. It reduces management overhead and increases efficiency. Key benefits include the following:

• Efficient batch operations: For large groups of related resources—such as a news feature page with hundreds of images and multiple JS or CSS files—assign the same tag to all resources. Then purge the entire group with one action.

• Improved O&M efficiency: Operations and development teams no longer need to track every resource URL. Instead, they focus on logical groupings—tags—to reduce complexity and avoid missing URLs.

• Greater business flexibility: Within the same application, assign different tags to different scenarios. purgeing by tag affects only the specified scenario—such as a sales promotion page—without impacting other scenarios.

• Consistent user experience: Ensure tightly coupled resources—such as frontend pages and their supporting static assets—update together. Avoid mismatches like new pages with old styles or partially outdated data.

Use cases

Common use cases include the following:

• Updating e-commerce sales promotion pages and associated assets

• Taking down special-topic content on news or media sites

• Switching content for multilingual or multi-version sites

• purgeing sub-application resources in a micro-frontend architecture

How it works

ESA uses HTTP headers as cache tags. A cache tag contains a header name and a header value separated by a colon:, for example, Cache-Tag:tag1,tag2,tag3. When you submit a task to purge the cache by tag:

1. ESA first determines whether the cache file on the POP is marked with a cache tag (default is Cache-Tag). If the cache tag does not exist, ESA skips the purge operation. If it exists, ESA matches the cache tag value.

2. ESA checks whether the tag value on the cached file matches the Purge Content you submitted. If it does not match, ESA skips the purge. If it matches, ESA purges the cache (default behavior: Mark as Expired).

Prerequisites

ESA's Purge cache by tag feature works by checking whether the cached content on ESA POPs contains specific cache tags. Therefore, when you use this feature, you must configure the origin server to add response headers that correspond to the cache tags for your resources. For configuration methods, see the following:

# /etc/nginx/nginx.conf

server {
    listen 80;
    server_name your-origin-domain.com;
    # Add tag to all resources under /images/
    location /images/ {
        add_header Cache-Tag "images";
        # ... other configuration
    }
    # ... other location blocks
}

Procedure

1. In the ESA console, choose Site Management. In the Website column, click your target site.

2. In the navigation pane on the left, choose Caching > Purge Cache.

3. On the Purge Cache tab, configure the purge rule and click Submit:

   • Type: Select By Tag.

   • Purge Method: Select Mark as Expired or Delete.

     Method	Description
     Mark as Expired	If a user requests content that matches a resource to be purged, the ESA node first performs an origin fetch to get the resource's Last-Modified information. If it matches the cached resource, the cached resource is returned. If not, the node pulls the new resource from the origin, returns it to the user, and caches the new resource.
     Delete	If a user requests content that matches a resource to be purged, the ESA node directly performs an origin fetch to pull the new resource, returns it to the user, and caches the new resource.

   • Purge Content: Enter the tag value to purge. Separate multiple values with ,, such as images.

   

4. After submitting the purge task, you can view detailed records and progress of resource purging on the Purge Records tab. The purge task is complete when the progress reaches 100%. The progress varies with the number of objects that you want to purge. The purge task may require some time to complete.

   

Cache purge examples

When you update images or page files on an e-commerce website, you need to delete the files and purge the corresponding ESA cache. An e-commerce website may have many cropped versions of an image in different sizes. When you delete an image, enumerating all of its cropped versions is inconvenient. Therefore, you can batch-delete the image files and the corresponding ESA cache by the image name. In addition, when you prepare for a promotional event, you need to continuously iterate on the event page during development. When you publish a new version of the page, you can delete all related files and the corresponding ESA cache by a specified version. Purging cache by tag significantly improves cache management efficiency:

Cache tag description

Availability