AMQP
The AMQP connector provides Apache Pekko Stream sources and sinks to connect to AMQP 0.9.1 servers (RabbitMQ, OpenAMQ, etc.).
AMQP 1.0 is currently not supported (Qpid, ActiveMQ, Solace, etc.).
Project Info: Apache Pekko Connectors AMQP | |
---|---|
Artifact | org.apache.pekko
pekko-connectors-amqp
1.1.0
|
JDK versions | OpenJDK 8 OpenJDK 11 OpenJDK 17 OpenJDK 21 |
Scala versions | 2.13.15, 2.12.20, 3.3.4 |
JPMS module name | pekko.stream.connectors.amqp |
License | |
API documentation | |
Forums | |
Release notes | GitHub releases |
Issues | Github issues |
Sources | https://github.com/apache/pekko-connectors |
Artifacts¶
val PekkoVersion = "1.1.3"
libraryDependencies ++= Seq(
"org.apache.pekko" %% "pekko-connectors-amqp" % "1.1.0",
"org.apache.pekko" %% "pekko-stream" % PekkoVersion
)
<properties>
<pekko.version>1.1.3</pekko.version>
<scala.binary.version>2.13</scala.binary.version>
</properties>
<dependencies>
<dependency>
<groupId>org.apache.pekko</groupId>
<artifactId>pekko-connectors-amqp_${scala.binary.version}</artifactId>
<version>1.1.0</version>
</dependency>
<dependency>
<groupId>org.apache.pekko</groupId>
<artifactId>pekko-stream_${scala.binary.version}</artifactId>
<version>${pekko.version}</version>
</dependency>
</dependencies>
def versions = [
PekkoVersion: "1.1.3",
ScalaBinary: "2.13"
]
dependencies {
implementation "org.apache.pekko:pekko-connectors-amqp_${versions.ScalaBinary}:1.1.0"
implementation "org.apache.pekko:pekko-stream_${versions.ScalaBinary}:${versions.PekkoVersion}"
}
The table below shows direct dependencies of this module and the second tab shows all libraries it depends on transitively.
Connecting to server¶
All the AMQP connectors are configured using a AmqpConnectionProvider
and a list of Declaration
There are several types of AmqpConnectionProvider
:
AmqpLocalConnectionProvider
which connects to the default localhost. It creates a new connection for each stage.AmqpUriConnectionProvider
which connects to the given AMQP URI. It creates a new connection for each stage.AmqpDetailsConnectionProvider
which supports more fine-grained configuration. It creates a new connection for each stage.AmqpConnectionFactoryConnectionProvider
which takes a raw ConnectionFactory. It creates a new connection for each stage.AmqpCachedConnectionProvider
which receive any other provider as parameter and caches the connection it provides to be used in all stages. By default it closes the connection whenever the last stage using the provider stops. Optionally, it takesautomaticRelease
boolean parameter so the connection is not automatically release and the user have to release it explicitly.
Please be aware that the basic usage of AmqpConnectionProvider
like this AmqpUriConnectionProvider(s"amqp://$host:$port")
has an issue with recovering connections, more details can be found in this issue
Sending messages¶
First define a queue name and the declaration of the queue that the messages will be sent to.
sourceval queueName = "amqp-conn-it-spec-simple-queue-" + System.currentTimeMillis()
val queueDeclaration = QueueDeclaration(queueName)
sourcefinal String queueName = "amqp-conn-it-test-simple-queue-" + System.currentTimeMillis();
final QueueDeclaration queueDeclaration = QueueDeclaration.create(queueName);
Here we used QueueDeclaration
configuration class to create a queue declaration.
With flow¶
Similarly as with Sink, the first step is to create Flow which accepts WriteMessage
s and forwards it’s content to the AMQP server. Flow emits WriteResult
s informing about publication result (see below for summary of delivery guarantees for different Flow variants).
AmqpFlow
is a collection of factory methods that facilitates creation of flows. Here we created a simple sink, which means that we are able to pass ByteString
s to the sink instead of wrapping data into WriteMessage
s.
Last step is to materialize and run the flow we have created.
sourceval settings = AmqpWriteSettings(connectionProvider)
.withRoutingKey(queueName)
.withDeclaration(queueDeclaration)
.withBufferSize(10)
.withConfirmationTimeout(200.millis)
val amqpFlow: Flow[WriteMessage, WriteResult, Future[Done]] =
AmqpFlow.withConfirm(settings)
val input = Vector("one", "two", "three", "four", "five")
val result: Future[Seq[WriteResult]] =
Source(input)
.map(message => WriteMessage(ByteString(message)))
.via(amqpFlow)
.runWith(Sink.seq)
sourcefinal AmqpWriteSettings settings =
AmqpWriteSettings.create(connectionProvider)
.withRoutingKey(queueName)
.withDeclaration(queueDeclaration)
.withBufferSize(10)
.withConfirmationTimeout(Duration.ofMillis(200));
final Flow<WriteMessage, WriteResult, CompletionStage<Done>> amqpFlow =
AmqpFlow.createWithConfirm(settings);
final List<String> input = Arrays.asList("one", "two", "three", "four", "five");
final List<WriteResult> result =
Source.from(input)
.map(message -> WriteMessage.create(ByteString.fromString(message)))
.via(amqpFlow)
.runWith(Sink.seq(), system)
.toCompletableFuture()
.get();
Various variants of AMQP flow offer different delivery and ordering guarantees:
AMQP flow factory | Description |
---|---|
AmqpFlow.apply | The most basic type of flow. Does not impose delivery guarantees, messages are published in a fire-and-forget manner. Emitted results have confirmed always set to true. |
AmqpFlow.withConfirm | Variant that uses asynchronous confirmations. Maximum number of messages simultaneously waiting for confirmation before signaling backpressure is configured with a bufferSize parameter. Emitted results preserve the order of messages pulled from upstream - due to that restriction this flow is expected to be slightly less effective than it’s unordered counterpart. |
AmqpFlow.withConfirmUnordered | The same as AmqpFlow.withConfirm with the exception of ordering guarantee - results are emitted downstream as soon as confirmation is received, meaning that there is no ordering guarantee of any sort. |
For FlowWithContext
counterparts of above flows see AmqpFlowWithContext
.
AmqpFlow.withConfirm
and AmqpFlow.withConfirmUnordered
are implemented using RabbitMQ’s extension to AMQP protocol (Publisher Confirms), therefore they are not intended to work with another AMQP brokers.
With sink¶
Create a sink, that accepts and forwards ByteString
s to the AMQP server.
AmqpSink
is a collection of factory methods that facilitates creation of sinks. Here we created a simple sink, which means that we are able to pass ByteString
s to the sink instead of wrapping data into WriteMessage
s.
Last step is to materialize and run the sink we have created.
sourceval amqpSink: Sink[ByteString, Future[Done]] =
AmqpSink.simple(
AmqpWriteSettings(connectionProvider)
.withRoutingKey(queueName)
.withDeclaration(queueDeclaration))
val input = Vector("one", "two", "three", "four", "five")
val writing: Future[Done] =
Source(input)
.map(s => ByteString(s))
.runWith(amqpSink)
sourcefinal Sink<ByteString, CompletionStage<Done>> amqpSink =
AmqpSink.createSimple(
AmqpWriteSettings.create(connectionProvider)
.withRoutingKey(queueName)
.withDeclaration(queueDeclaration));
final List<String> input = Arrays.asList("one", "two", "three", "four", "five");
CompletionStage<Done> writing =
Source.from(input).map(ByteString::fromString).runWith(amqpSink, system);
Receiving messages¶
Create a source using the same queue declaration as before.
The bufferSize
parameter controls the maximum number of messages to prefetch from the AMQP server.
Run the source and take the same amount of messages as we previously sent to it.
sourceval amqpSource: Source[ReadResult, NotUsed] =
AmqpSource.atMostOnceSource(
NamedQueueSourceSettings(connectionProvider, queueName)
.withDeclaration(queueDeclaration)
.withAckRequired(false),
bufferSize = 10)
val result: Future[immutable.Seq[ReadResult]] =
amqpSource
.take(input.size)
.runWith(Sink.seq)
sourcefinal Integer bufferSize = 10;
final Source<ReadResult, NotUsed> amqpSource =
AmqpSource.atMostOnceSource(
NamedQueueSourceSettings.create(connectionProvider, queueName)
.withDeclaration(queueDeclaration)
.withAckRequired(false),
bufferSize);
final CompletionStage<List<ReadResult>> result =
amqpSource.take(input.size()).runWith(Sink.seq(), system);
This is how you send and receive message from AMQP server using this connector.
Using Pub/Sub¶
Instead of sending messages directly to queues, it is possible to send messages to an exchange and then provide instructions to the AMQP server what to do with incoming messages. We are going to use the fanout type of the exchange, which enables message broadcasting to multiple consumers. We are going to do that by using an exchange declaration for the sink and all of the sources.
sourceval exchangeName = "amqp-conn-it-spec-pub-sub-" + System.currentTimeMillis()
val exchangeDeclaration = ExchangeDeclaration(exchangeName, "fanout")
sourcefinal String exchangeName = "amqp-conn-it-test-pub-sub-" + System.currentTimeMillis();
final ExchangeDeclaration exchangeDeclaration =
ExchangeDeclaration.create(exchangeName, "fanout");
The sink for the exchange is created in a very similar way.
sourceval amqpSink = AmqpSink.simple(
AmqpWriteSettings(connectionProvider)
.withExchange(exchangeName)
.withDeclaration(exchangeDeclaration))
sourcefinal Sink<ByteString, CompletionStage<Done>> amqpSink =
AmqpSink.createSimple(
AmqpWriteSettings.create(connectionProvider)
.withExchange(exchangeName)
.withDeclaration(exchangeDeclaration));
For the source, we are going to create multiple sources and merge them using Apache Pekko Streams operators.
sourceval fanoutSize = 4
val mergedSources = (0 until fanoutSize).foldLeft(Source.empty[(Int, String)]) {
case (source, fanoutBranch) =>
source.merge(
AmqpSource
.atMostOnceSource(
TemporaryQueueSourceSettings(
connectionProvider,
exchangeName).withDeclaration(exchangeDeclaration),
bufferSize = 1)
.map(msg => (fanoutBranch, msg.bytes.utf8String)))
}
sourcefinal int fanoutSize = 4;
final int bufferSize = 1;
Source<Pair<Integer, String>, NotUsed> mergedSources = Source.empty();
for (int i = 0; i < fanoutSize; i++) {
final int fanoutBranch = i;
mergedSources =
mergedSources.merge(
AmqpSource.atMostOnceSource(
TemporaryQueueSourceSettings.create(connectionProvider, exchangeName)
.withDeclaration(exchangeDeclaration),
bufferSize)
.map(msg -> Pair.create(fanoutBranch, msg.bytes().utf8String())));
}
We merge all sources into one and add the index of the source to all incoming messages, so we can distinguish which source the incoming message came from.
Such sink and source can be started the same way as in the previous example.
Using rabbitmq as an RPC mechanism¶
If you have remote workers that you want to incorporate into a stream, you can do it using rabbit RPC workflow RabbitMQ RPC
sourceval amqpRpcFlow = AmqpRpcFlow.simple(
AmqpWriteSettings(connectionProvider).withRoutingKey(queueName).withDeclaration(queueDeclaration))
val (rpcQueueF: Future[String], probe: TestSubscriber.Probe[ByteString]) = Source(input)
.map(s => ByteString(s))
.viaMat(amqpRpcFlow)(Keep.right)
.toMat(TestSink.probe)(Keep.both)
.run()
sourcefinal Flow<ByteString, ByteString, CompletionStage<String>> ampqRpcFlow =
AmqpRpcFlow.createSimple(
AmqpWriteSettings.create(connectionProvider)
.withRoutingKey(queueName)
.withDeclaration(queueDeclaration),
1);
Pair<CompletionStage<String>, TestSubscriber.Probe<ByteString>> result =
Source.from(input)
.map(ByteString::fromString)
.viaMat(ampqRpcFlow, Keep.right())
.toMat(TestSink.probe(system), Keep.both())
.run(system);
Acknowledging messages downstream¶
Committable sources return CommittableReadResult
which wraps the ReadResult
and exposes the methods ack
and nack
.
Use ack
to acknowledge the message back to RabbitMQ. ack
takes an optional boolean parameter multiple
indicating whether you are acknowledging the individual message or all the messages up to it.
Use nack
to reject a message. Apart from the multiple
argument, nack
takes another optional boolean parameter indicating whether the item should be requeued or not.
sourceval amqpSource = AmqpSource.committableSource(
NamedQueueSourceSettings(connectionProvider, queueName)
.withDeclaration(queueDeclaration),
bufferSize = 10)
val result: Future[immutable.Seq[ReadResult]] = amqpSource
.mapAsync(1)(businessLogic)
.mapAsync(1)(cm => cm.ack().map(_ => cm.message))
.take(input.size)
.runWith(Sink.seq)
val nackedResults: Future[immutable.Seq[ReadResult]] = amqpSource
.mapAsync(1)(businessLogic)
.take(input.size)
.mapAsync(1)(cm => cm.nack(multiple = false, requeue = true).map(_ => cm.message))
.runWith(Sink.seq)
sourcefinal Integer bufferSize = 10;
final Source<CommittableReadResult, NotUsed> amqpSource =
AmqpSource.committableSource(
NamedQueueSourceSettings.create(connectionProvider, queueName)
.withDeclaration(queueDeclaration),
bufferSize);
final CompletionStage<List<ReadResult>> result =
amqpSource
.mapAsync(1, this::businessLogic)
.mapAsync(1, cm -> cm.ack(/* multiple */ false).thenApply(unused -> cm.message()))
.take(input.size())
.runWith(Sink.seq(), system);
final CompletionStage<List<ReadResult>> nackedResults =
amqpSource
.take(input.size())
.mapAsync(1, this::businessLogic)
.mapAsync(
1,
cm ->
cm.nack(/* multiple */ false, /* requeue */ true)
.thenApply(unused -> cm.message()))
.runWith(Sink.seq(), system);