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Diffstat (limited to 'guides')
| -rw-r--r-- | guides/source/asset_pipeline.md | 34 |
1 files changed, 21 insertions, 13 deletions
diff --git a/guides/source/asset_pipeline.md b/guides/source/asset_pipeline.md index ed76ab8f22..20afd4ef31 100644 --- a/guides/source/asset_pipeline.md +++ b/guides/source/asset_pipeline.md @@ -917,19 +917,27 @@ end ### CDNs -If your assets are being served by a CDN, ensure they don't stick around in your -cache forever. This can cause problems. If you use -`config.action_controller.perform_caching = true`, Rack::Cache will use -`Rails.cache` to store assets. This can cause your cache to fill up quickly. - -Every cache is different, so evaluate how your CDN handles caching and make sure -that it plays nicely with the pipeline. You may find quirks related to your -specific set up, you may not. The defaults NGINX uses, for example, should give -you no problems when used as an HTTP cache. - -If you want to serve only some assets from your CDN, you can use custom -`:host` option of `asset_url` helper, which overwrites value set in -`config.action_controller.asset_host`. +CDN stands for [Content Delivery +Network](http://en.wikipedia.org/wiki/Content_delivery_network), they are +primarily designed to cache assets all over the world so that when a browser +requests the asset, a cached copy will be geographically close to that browser. +If you are serving assets directly from your Rails server in production, the +best practice is to use a CDN in front of your application. + +A common pattern for using a CDN is to set your production application as the +"origin" server. This means when a browser requests an asset from the CDN and +there is a cache miss, it will grab the file from your server on the fly and +then cache it. For example if you are running a Rails application on +`example.com` and have a CDN configured at `mycdnsubdomain.fictional-cdn.com`, +then when a request is made to `mycdnsubdomain.fictional- +cdn.com/assets/smile.png`, the CDN will query your server once at +`example.com/assets/smile.png` and cache the request. The next request to the +CDN that comes in to the same URL will hit the cached copy. When the CDN can +serve an asset directly the request never touches your Rails server. Since the +assets from a CDN are geographically closer to the browser, the request is +faster, and since your server doesn't need to spend time serving assets, it can +focus on serving application code as fast as possible. + ```ruby asset_url 'image.png', :host => 'http://cdn.example.com' |