Origin Server Redundancy

Origin Redundancy Settings

When configuring redundancy for OvenMediaEngine's Low-Latency HLS Origin Servers (or HLS Origin Servers), you can make the Segment file names on the Primary and Secondary Origin Servers the same through the Origin redundancy setting. This ensures that the Edge Server or CDN Cache Server connects to the Secondary Origin Server instead of the Primary Origin Server and downloads the same content seamlessly if the Primary Origin Server fails.

Enable <Publishers><LLHLS><ServerTimeBasedSegmentNumbering> (or <Publishers><HLS><ServerTimeBasedSegmentNumbering>) in Server.xml as follows:

<?xml version="1.0" encoding="UTF-8"?>
<Server version="8">
  ...
  <VirtualHosts>
    <VirtualHost>
      <Applications>
        <Application>
          <Publishers>
            ...
            <LLHLS>
              <ServerTimeBasedSegmentNumbering>true</ServerTimeBasedSegmentNumbering>
            </LLHLS>
          </Publishers>
        </Application>
      </Applications>
    </VirtualHost>
  </VirtualHosts>
</Server>

This feature generates segment file names based on server time, so you must synchronize the time on your primary and secondary origin servers.

Default Query String Settings

You can control the fundamental operations of Low-Latency HLS (or Legacy HLS) via the <DefaultQueryString>.

Set in <Publishers><LLHLS><DefaultQueryString> (or <Publishers><HLS><DefaultQueryString>) in Server.xml as follows:

<?xml version="1.0" encoding="UTF-8"?>
<Server version="8">
  ...
  <VirtualHosts>
    <VirtualHost>
      <Applications>
        <Application>
          <Publishers>
            ...
            <LLHLS>
              <DefaultQueryString>
		        <Query>
				  <Key>_HLS_legacy</Key>
				  <Value>NO</Value>
		        </Query>
		        <Query>
				  <Key>_HLS_rewind</Key>
				  <Value>YES</Value>
			    </Query>
			  </DefaultQueryString>
            </LLHLS>
          </Publishers>
        </Application>
      </Applications>
    </VirtualHost>
  </VirtualHosts>
</Server>

This setting is ignored if the playback URL already has a query string appended to it.

Key	Value	Description
_HLS_legacy	YES | NO * Default: NO	Sets the _HLS_legacy value to YES will remove partial segment information from LL-HLS playlists, making them work the same as legacy HLS like HLSv6. * LL-HLS Only
_HLS_rewind	YES | NO * Default: YES	If the _HLS_rewind value is set to YES and the Live Rewind feature is enabled, old segment information will be included in the playlist.

Using Propagatet Query String

When you enable <PropagateQueryString>, the query string included in the initial Master Playlist request is automatically carried over to all sub-requests (Media Playlist, Segment, and Partial Segment). By including session keys, authentication tokens, etc., in the query string and utilizing this feature, content access control becomes easier as all requests can be verified at the CDN level.

Set the <Publishers><LLHLS><PropagateQueryString> (or <Publishers><HLS><PropagateQueryString>) in Server.xml like this:

<?xml version="1.0" encoding="UTF-8"?>
<Server version="8">
  ...
  <VirtualHosts>
    <VirtualHost>
      <Applications>
        <Application>
          <Publishers>
            ...
            <LLHLS>
              <OriginMode>true</OriginMode>
              <PropagateQueryString>true</PropagateQueryString>
            </LLHLS>
          </Publishers>
        </Application>
      </Applications>
    </VirtualHost>
  </VirtualHosts>
</Server>

You should take care not to include sensitive information in the Query String directly.

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 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.