Does EMA handle connection failover like RFA?

Ripley79

Within RFA, they include a very useful feature called "Warm Standby". This is highlighted within the "Features of RFA" section that I'm presently using that will automatically failover to a standby connection if my primary connection fails. Do I get something similar if I use EMA?

Steven McCoy

No, EMA and the underlying UPA ValueAdd library do not support warm standby only cold standby.

For EMA here is a summary:

v3.0.1 - Fixes cold standby support.
v3.0.0 - No standby support at all.

Hot standby support is only implemented within TREP as part of the ADH server.

piyasak.chansaengsai

@Ripley79, the connection failover is listed in the new features of EMA 3.0.1.

My configuration is as follows:

<ConsumerGroup>
	<!-- DefaultConsumer parameter defines which consumer configuration is used by OmmConsumer			-->
	<!-- if application does not specify it through OmmConsumerConfig::consumerName()					-->
	<!-- first consumer on the ConsumerList is a default consumer if this parameter is not specified	-->
	<DefaultConsumer value="Consumer_3"/>
	<ConsumerList>
		<Consumer>
			<Name value="Consumer_1"/>


			<!-- Channel is optional: defaulted to "RSSL_SOCKET + localhost + 14002" -->
			<Channel value="Channel_1"/>


			<!-- Logger is optional: defaulted to "File + Success" -->
			<Logger value="Logger_1"/>


			<!-- Dictionary is optional: defaulted to "ChannelDictionary" -->
			<Dictionary value="Dictionary_1"/>
		</Consumer>
		<Consumer>
			<Name value="Consumer_2"/>
			<!-- ChannelSet is optional: defaulted to "RSSL_SOCKET + localhost + 14002" -->
			<ChannelSet value="Channel_1, Channel_2"/>
			<Logger value="Logger_2"/>
			<Dictionary value="Dictionary_2"/>
		</Consumer>
        <Consumer>
        <Name value="Consumer_3"/>
        <!-- ChannelSet is optional -->
        <ChannelSet value="Channel_1, Channel_2"/>
        <!-- Logger is optional: defaulted to "File + Success" -->
        <Logger value="Logger_1"/>
        <!-- Dictionary is optional: defaulted to "ChannelDictionary" -->
        <Dictionary value="Dictionary_1"/>
        </Consumer>
	</ConsumerList>
</ConsumerGroup>
<ChannelGroup>
	<ChannelList>
		<Channel>
			<Name value="Channel_1"/>


			<!-- ChannelType possible values are: -->
			<!-- ChannelType::RSSL_SOCKET    - TCP IP connection type -->
			<!-- ChannelType::RSSL_HTTP      - Http tunnel connection type -->
			<!-- ChannelType::RSSL_ENCRYPTED - Https tunnel connection type -->
			<!-- ChannelType::RSSL_RELIABLE_MCAST - Reliable multicast connection type -->
			<ChannelType value="ChannelType::RSSL_SOCKET"/>


			<!-- CompressionType is optional: defaulted to None -->
			<!-- possible values: None, ZLib, LZ4 -->
			<CompressionType value="CompressionType::None"/>
			<GuaranteedOutputBuffers value="5000"/>


			<!-- ConnectionPingTimeout is optional: defaulted to 30000 -->
			<ConnectionPingTimeout value="30000"/>
			<!-- TcpNodelay is optional: defaulted to 1 -->
			<!-- possible values: 1 (tcp_nodelay option set), 0 (tcp_nodelay not set) -->
			<TcpNodelay value="1"/>
			<Host value="apis23"/>
			<Port value="14002"/>
			<XmlTraceToFile value="1"/>
		</Channel>
		<Channel>
			<Name value="Channel_2"/>
			<ChannelType value="ChannelType::RSSL_SOCKET"/>
			<CompressionType value="CompressionType::None"/>
			<GuaranteedOutputBuffers value="5000"/>
			<Host value="localhost"/>
			<Port value="14002"/>
		</Channel>

The DefaultConsumer was set to Consumer_3, so my EMA consumer app connected to the host listed in Channel_1. When the ADS in Channel_1 went down, my app switched to another provider running on localhost as expected.

Steven McCoy

That is cold standby, not warm standby.