Overview
CDN 2.3 implements the following features in addition to CDN 2.1 and 2.2:
- prevention of redundant transcoding of the same stream on two or more transcoders in CDN
Prevention of redundant transcoding of the same stream on two or more transcoders in CDN
CDN 23 allows to prevent redundant transcoding of the same stream published to CDN on two or more transcoders in the same group. This can occur in large CDNs with big amount of incoming and outgoing media traffic, when a many subscribers connecting simultaneously to the CDN servers. It creates excessive load on transcoders which may lead to servers out of work..
To solve the problem, in every CDN group the special node with Controller role should be allocated which receives stream information from all th CDN nodes and collects current CDN state. The nodes with Edge role should request Controller node if it is available to choose a route for a stream playback. If the stream is already transcoded on any Transcoder node, Controller node does not allow to build the route for the stream playback trough another Trancsoder. If Controller node is not available, Edge node should choose a route for a stream playback according to CDN 2.1 method.
Controller node should not be used to publish or play any streams.
Configuration
Controller role should be set to node with the following parameter
cdn_role=controller
Controller request timeout can be defined on Edge node with the following parameter
cdn_controller_request_timeout=5000
The timeout is set in milliseconds, 5000 ms by default.
Controller response caching duration can be defined on Edge node with the following parameter
cdn_controller_response_cache_expire=10000
The cache duration is set in milliseconds, 10000 ms by default.
Controller response timeout and caching parameters should be set only on Edge nodes.
Redundant stream transcoding checking with REST API
Redundant stream transcoding can be checked with REST query to Edge server.
REST query should be HTTP/HTTPS POST request as follows:
- HTTP: http://test.flashphoner.com:8081/rest-api/cdn/show_redundant_transcodings
- HTTPS: https://test.flashphoner.com:8444/rest-api/cdn/show_redundant_transcodings
Where:
- test.flashphoner.com - WCS server address
- 8081 - a standard WCS REST / HTTP port
- 8444 - a standard WCS HTTPS port
- rest-api - mandatory part of URL
- /cdn/show_redundant_transcodings - REST query used
REST queries should be sent to Edge server.
REST queries and responses
REST query | REST query body example | REST response body example | Response states | Description |
|---|---|---|---|---|
/cdn/show_redundant_transcodings | {"test6":"192.168.1.17,192.168.1.18"}
| 200 – Redundant transcoding found 404 - No redundant transcoding | Check redundant transcoding |
Parameters
Description | Example |
|---|---|
Stream name |
|
| Transcoding nodes list | 192.168.1.17,192.168.1.18 |
Backward compatibility with CDN 2.2, 2.1, 2.0
For previous CDN versions node, Controller node is Origin.
CDN 2.1 nodes will choose a route to stream playback without Controller node even if this node is in the group.
Known limits
To choose a stream playback route using Controller node, Edge node should be in the same group, and this group must be set in CDN node settings:
cdn_groups=g1
Controller node choose all the routes through Transcoder nodes in the same group only.
Controller node without any group set cannot be used to choose a route.