Function Introduction

Range origin fetching refers to CDN nodes carrying Range request headers when receiving user requests, and when the origin server receives a Range request, it returns the corresponding range of content data to the CDN. With Range origin fetching enabled, CDN nodes can cache files in the form of segments. For Range requests, it effectively improves file distribution efficiency, reduces initial packet delay, and increases cache utilization while reducing unnecessary origin fetching.

When enabling or disabling Range origin fetching, the corresponding situations are as follows:

Disabling Range Origin Fetching

When the client initiates a Range request and the CDN node has no cache, it defaults to pass the client's Range request to the origin. Regardless of whether the origin server responds with a 206 or 200 status code, the CDN does not cache and passes the origin server's status code and content to the client.
When the client initiates a request for the complete file and the CDN node has no cache, it passes the client's request to the origin, the origin server responds with a 200 status code, the CDN caches the file, and responds with a 200 status code and content to the client.

Enabling Range Origin Fetching

Regardless of whether the client initiates a Range request or not, when the CDN node has no cache, it fetches segments according to the configured Range size. If the origin server responds with a 206 status code, the CDN caches the corresponding segment content and responds with a 206 (for Range requests) or 200 (for complete file requests) to the client.
When the client initiates a Range request and the CDN has cached the file content within the Range, it directly responds with a 206 status code and corresponding cached content range to the client.

Range origin fetching is disabled by default, and the CDN fetches the origin based on the client's request method, whether with or without a Range request header.

Note

If the client has a Range request, the CDN cannot cache the corresponding file by default. You need to enable Complete File Origin Fetching or Range origin fetching.

Applicable Scenarios

When the client has Range requests and the origin server supports Range and can respond with specified range content data, it is recommended to enable Range origin fetching to improve file distribution efficiency and cache utilization.

Typical scenarios for enabling Range origin fetching include large file scenarios such as videos and apps on the origin server.

Considerations

Before enabling Range origin fetching, confirm whether the origin server supports Range requests, i.e., whether the origin server can respond with 206 file segment content for the specified range, and also confirm whether the origin server response header contains "Transfer-Encoding: chunked". If the origin server does not support Range requests, or the origin server may respond with "Transfer-Encoding: chunked", you can submit a ticket to configure the "Complete File Origin Fetching" function. After this function is enabled, when the client initiates a Range request, the CDN node will fetch the complete file from the origin and cache it, and respond with the Range data.

Note

If the Range requested by the client is towards the end of the file, after enabling Complete File Origin Fetching, the client may need to wait for a long time to obtain the Range content for the first request, resulting in lower distribution efficiency.

When enabling Range origin fetching, the CDN will split the user requests (whether the original request is a Range request or not) into several Range requests to the origin. For example, for a 100MB file, with Range origin fetching enabled, the CDN needs to fetch the complete file 100 times, which may increase the number of origin fetching requests and concurrency to some extent. Please set the segment size reasonably. The default Range segment size is 1MB, i.e., if the client requests Range: bytes=0-100, the CDN node will expand the Range request to 1MB when fetching from the origin.
Please clarify whether to enable Range origin fetching when adding a new domain name, as well as the specific segment size for enabling Range origin fetching. Once the domain name is CNAMEd to our service and generates traffic, it is recommended not to change the enabling status or segment size of Range origin fetching easily, as it may result in higher origin fetching. If there is indeed an adjustment requirement, please specify it when submitting the ticket.

Configuration Instructions

This feature does not currently support self-service configuration by customers. If you need to use it, please please contact our customer support team via hotline (852)31000000 or email global.noc@chinatelecomglobal.com for manual setup.

Please provide the following information:

Segment size for origin fetching, default is 1MB; if you need to set it to another value, please provide detailed instructions.
Range of segment ranges, default is domain granularity; if you need to set it to only specific files, please specify the specific file range, such as xx directory, or xx file suffixes (such as .mp4, .flv, etc.).

Content Delivery Network