After you enable the Gzip compression feature, Alibaba Cloud CDN points of presence (POPs) use Gzip compression to compress resources before the resources are returned to clients. The Gzip compression feature reduces file sizes, accelerates file distribution, and reduces bandwidth consumption.
Background information
Compression is divided into Gzip compression and Brotli compression. The Gzip compression feature uses the Gzip compression algorithm. For more information about Brotli compression, see Configure Brotli compression.
You can use the Gzip compression or Brotli compression feature to compress the files on the origin server whose size ranges from 1 KB to 10 KB. Files that are smaller than 1 KB or larger than 10 MB are not compressed.
The Gzip compression feature supports the following formats: text/xml, text/plain, text/css, application/javascript, application/x-javascript, application/rss+xml, text/javascript, image/tiff, image/svg+xml, application/json, and application/xml.
If a request carries the
Accept-Encoding: gziprequest header, the client wants to use Gzip compression to compress the requested resources.If a response from the origin server carries the
Content-Encoding: gzipresponse header, the resources returned to the client are Gzip-compressed.
Usage notes
The Gzip compression feature is compatible with all browsers. The Brotli compression feature is not compatible with outdated browsers. You can query whether a browser supports Brotli compression based on your business requirements.
When Alibaba Cloud CDN compresses static files, the MD5 values of the files are changed. If MD5 verification is used in the service logic for your website, clients verify the MD5 values of files that are retrieved from POPs. If the MD5 value of a file is different from the MD5 value in the response header, the client considers the file download failed. In this case, you need to disable Gzip compression and Brotli compression.
If compression is enabled on the origin server and the response from the origin server contains
Content_Encoding, compression on POPs does not take effect.If both the Gzip compression and Brotli compression features are enabled, and the
Accept-Encodingrequest header contains bothbrandgzip, only the Brotli compression feature takes effect.If both HTML optimization and compression are enabled, HTML optimization does not take effect. Alibaba Cloud CDN only compresses files.
Image files in common formats, including PNG, JPG, and JPEG, and video files in common formats, including MP4, AVI, and WMV, are already compressed. The Gzip compression and Brotli compression features do not take effect for these files. We recommend that you disable Gzip compression and Brotli compression for such files. If you want to reduce the size of image files, you can use the image editing feature. For more information, see Image editing overview. If you want to reduce the size of video files, you can use the video transcoding feature. For more information, see Audio and video transcoding.
Procedure
Log on to the Alibaba Cloud CDN console.
In the left-side navigation pane, click Domain Names.
On the Domain Names page, find the domain name that you want to manage and click Manage in the Actions column.
In the left-side navigation tree of the domain name, click Optimization.
In the Gzip Compression section, turn on Gzip Compression.
You can compare the format of a file before and after the Gzip compression feature is enabled. If the file name extension is .gzip, the file is compressed.
FAQ
Why does Gzip compression fail to take effect for requests redirected to the origin server?