CDN Cache Control

Control Origin Cache

You can specify how long content should be cached on edge servers or CDN cache servers by adding a Cache-Control header to the HTTP response.

Set the <Publishers><LLHLS><CacheControl> in Server.xml like this:

<?xml version="1.0" encoding="UTF-8"?>
<Server version="8">
  ...
  <VirtualHosts>
    <VirtualHost>
      <Applications>
        <Application>
          <Publishers>
            ...
            <LLHLS>
              <OriginMode>true</OriginMode>
              <CacheControl>
                <MasterPlaylistMaxAge>0</MasterPlaylistMaxAge>
                <ChunklistMaxAge>0</ChunklistMaxAge>
                <ChunklistWithDirectivesMaxAge>60</ChunklistWithDirectivesMaxAge>
                <SegmentMaxAge>-1</SegmentMaxAge>
                <PartialSegmentMaxAge>-1</PartialSegmentMaxAge>
              </CacheControl>
            </LLHLS>
          </Publishers>
        </Application>
      </Applications>
    </VirtualHost>
  </VirtualHosts>
</Server>

Element	Description
MasterPlaylistMaxAge	Specifies the max-age of the Master Playlist. It will not change while the Stream is being created.
ChunklistMaxAge	Specifies the max-age of the Media Playlist. It must always respond with the latest Media Playlist and is a URL without Delivery Directives for LL-HLS. Therefore, it should be cached as short as possible or not at all.
ChunklistWithDirectivesMaxAge	Specifies the max-age of the Media Playlist with the Low-Latency HLS Delivery Directives. The currently supported Delivery Directives are _HLS_msn and _HLS_part. It is a Playlist with Segment numbers and Partial Segment numbers, and this URL is unique while the Stream is being created and can be cached for a long time because the content of the same URL does not change.
SegmentMaxAge	Specifies the max-age of the Segment File. The URL of the Segment File is unique while the Stream is being created and can be cached for a long time because the content of the same URL does not change.
PartialSegmentMaxAge	Specifies the max-age of the Partial Segment File. The URL of the Partial Segment File is unique while the Stream is being created and can be cached for a long time because the content of the same URL does not change.

<CacheControl> Elements

Element	Description
0	CacheControl: no-cache, no-store Instructs not to cache the content at all, always fetching new data from the Server.
Greater than 0	CacheControl: max-age=<seconds> Specifies the duration for which the Cache remains valid.
-1	Without CacheControl header Indicates that no specific Cache Header will be sent from the Origin. In this case, caching may not be used at all, or the CDN or Cache server's policies may be applied, or the default Cache behavior of the Client or Browser may be followed.

<CacheControl> can be used with 0 and positive values, while using -1 may result in unexpected caching behaviors, so caution is advised.

Cache Validation

Enabling this feature allows identification of whether the cached resource version matches the resource in OvenMediaEngine. When the HTTP request includes the If-None-Match: "<etag_value>" header, it compares the resource Etag with the OvenMediaEngine's resource Etag, and if the values match, it returns 304 Not-Modified.

Set the <Modules><ETag> in Server.xml like this:

<Server>
  <Modules>
    <ETag>
      <Enable>true</Enable>
    </ETag>
  </Modules>
</Server>

When enabled, an Etag header will be added to all HTTP responses.