Content Caching for Cloud Load Balancers

  • Last updated on: 2018-10-24
  • Authored by: Rackspace Support

The Cloud Load Balancers product has a Content Caching feature that stores recently-accessed files on the load balancer so that web clients can easily retrieve them.

Enable content caching

You can enable content caching through the Cloud Load Balancers API or the Cloud Control Panel.

Content caching can be enabled or disabled for a load balancer in the Cloud Control Panel by going to its details screen, scrolling down to the Optional Features section, and clicking the pencil icon next to Content Caching.

Benefits of content caching

Content caching improves the performance of a web site by temporarily storing data that was recently accessed. While it’s cached, requests for that data will be served by the load balancer instead of making another query to a web server behind it.

The result is improved response times for those requests and less load on the web server.

What kind of files work well with content caching?

Content caching works well for files that don’t change or that rarely change. Most images and static content are good candidates for content caching.

You don’t want to cache files that would change regularly or would be dynamically generated for different site visitors.

Caching details

Is there a maximum file size that can be cached?

The maximum file size per cached item is 2 MB.

How long is content cached?

Up to 10 minutes, depending on the load and amount of traffic being handled by the load balancer host.

If a cached file is requested shortly before it will expire, the load balancer will retrieve a new copy of the file early to prevent the file from being uncached during a period of heavy traffic.

Can I choose how long files will be cached?

No, not at this time. You cannot purge a file from the cache manually, but it will be automatically removed when its cache time expires.

Do nodes share a cache?

No. Each node has its own cache, separate from other load-balanced nodes.

Does cache carry over in a failover situation?

No. If a failover occurs the load balancer will retrieve a fresh copy of a file from the failover host.

File types

What file types are supported for content caching?

At this time the following file extensions are cached:


Can I exclude specific file types?

Yes. Have your web server set the Cache-Control header to no-cache for requests for the file types you don’t want cached.

You can set this header in apache by adding a config block similar to the following to your apache config:

<FilesMatch ".(ico|flv|jpg|jpeg)$">
    Header set Cache-Control "no-cache"

Replace the extensions in the “ico|flv|jpg|jpeg” section with the extensions for which you want to bypass caching, making sure to put a “|” character between each extension.

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