monix / monix-connect

A set of stream connectors and integrations for Monix.


Monix Connect

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Warning: Mind that the project is yet in early stages and its API is likely to be changed.

Monix Connect is an initiative to implement stream integrations for Monix. A connector describes the connection between the application and a specific data point, which could be a file, a database or any system in which the appication can interact by sending or receiving information. Therefore, the aim of this project is to catch the most common connections that users could need when developing reactive applications with Monix, these would basically reduce boilerplate code and furthermore, will let the users to greatly save time and complexity in their implementing projects.

The latest stable version of monix-connect is compatible with Monix 3.x, Scala 2.12.x and 2.13.x, you can import all of the connectors by adding the following dependency (find and fill your release version):

libraryDependencies += "io.monix" %% "monix-connect" % "VERSION"

But you can also only include to a specific connector to your library dependencies, see below how to do so and how to get started with each of the available connectors.


  1. Akka
  2. DynamoDB
  3. Hdfs
  4. Parquet
  5. Redis
  6. S3



This module makes interoperability with akka streams easier by simply defining implicit extended classes for reactive stream conversions between akka and monix.

The three main core abstractions defined in akka streams are Source, Flow and Sink, they were designed following the JVM reactive streams standards, meaning that under it's design they implement the Publisher and Subscriber contract. Which at the end it means that they can interoperate with other libraries that also implements the reactive stream specification, such as Monix Reactive. So this module aims to provide a nice interoperability between these two reactive streams libraries.

In order to achieve it, this module will provide an extended conversion method for each of the stream abstractions mentioned before. These implicit extended methods can be imported from: Therefore, under the scope of the import, the signatures .asObservable and .asConsumer will be available for the Source, Flow, and Sink.

The below table shows in more detail the specs for the conversion from akka stremas to monix:

Akka Monix Akka -> Monix Monix -> Akka
Source[+In, +Mat] Observable[+In] source.asObservable[In] observable.asSource[In]
Flow[-In, +Out, +Mat] Consumer[-In, +Out] flow.asConsumer[Out] -
Sink[-In, +Out <: Future[Mat]] Consumer[-In, +Mat] sink.asConsumer[Mat] consumer.asSink[In]

Note that two methods does not need to be typed as it has been done explicitly in the example table, the compiler will infer it for you.

Also, in order to perform these conversion it is required to have an implicit instance of and monix.execution.Scheduler in the scope.

Set up

Add the following dependency to get started:

libraryDependencies += "io.monix" %% "monix-akka" % "0.1.0"

Getting started

The following code shows how these implicits can be initialized, but Scheduler and ActorSystem can be initialized differently and configured differently depending on the use case.


val actorSystem: ActorSystem = ActorSystem("Akka-Streams-InterOp") 
implicit val materializer = ActorMaterializer() 

Akka -> Monix

Let's see an example for converting an Source[+In, +Mat] to Observable[+In]:

val elements = 1 until 50

val ob: Observable[Int] = Source.from(elements).asObservable //`asObservable` converter as extended method of source.

ob.toListL.runSyncUnsafe() should contain theSameElementsAs elements

In this case we have not needed to consume the Observable since we directly used an operator that collects to a list .toList, but note that in case you need to use an specific consumer, you can also directly call consumeWith, as a shortcut for source.asObservable.consumeWith(consumer), see an example below:

//given the same `elements` and `source` as above example`

val t: Task[List[Int]] = source.consumeWith(Consumer.toList) //`consumeWith` as extended method of `Source`

t.runSyncUnsafe() should contain theSameElementsAs elements

On the other hand, see how to convert an Sink[-In, +Out <: Future[Mat]] into a Consumer[+In, +Mat].

val foldSumSink: Sink[Int, Future[Int]] = Sink.fold[Int, Int](0)((acc, num) => acc + num)

val (consumer: Consumer[Int, Int]) = foldSumSink.asConsumer[Int] //`asConsumer` as an extended method of `Sink`
val t: Task[Int] = Observable.fromIterable(Seq(1, 2, 3)).consumeWith(consumer)

//then the future value of `t` should be 6

Finally, you can also convert Flow[-In, +Out, +Mat] into Consumer[+In, +Mat] in the same way you did with Sink in the previous example.

val foldSumFlow: Flow[Int, Int, NotUsed] = Flow[Int].fold[Int](0)((acc, num) => acc + num)

val (consumer: Consumer[Int, Int]) = foldSumFlow.asConsumer //`asConsumer` as an extended method of `Flow`
val t: Task[Int] = Observable.fromIterable(Seq(1, 2, 3)).consumeWith(consumer)

//then the future value of `t` should be 6

Notice that this interoperability would allow the Monix user to take advantage of the already pre built integrations from Alpakka or any other Akka Streams implementation.

Monix -> Akka

On the other hand, for converting from Monix Observable[+In] to Akka Streams Source[+In, NotUsed] we would use the conversion signature asSource.

val f: Future[Seq[Long]] = Observable.range(1, 100).asSource.runWith(Sink.seq) 
//eventualy will return a sequence from 1 to 100

Finally, for converting from Sink[-In, +Out <: Future[Mat]] to Consumer[-In, +Mat].

val sink: Sink[Int, Future[String]] = Sink.fold[String, Int]("")((s, i) => s + i.toString)
val t: Task[String] = Observable.fromIterable(1 until 10).consumeWith(sink.asConsumer[String])
//eventually will return "123456789"



Amazon DynamoDB is a key-value and document database that performs at any scale in a single-digit millisecond, a key component for many platforms of the world's fastest growing enterprises that depend on it to support their mission-critical workloads.

The DynamoDB api provides a large list of operations (create, describe, delete, get, put, batch, scan, list and more...), all them are simply designed in request and response pattern, in which from the api prespective, they have to respectively implement DynamoDbRequest and DynamoDbResponse.

The fact that all types implements either Request or Response type makes possible to create on top of that an abstraction layer that executes the received requests and retunrn a future value with the respective response.

From there one, this connector provides two pre built implementations of a monix transformer and consumer that implements the mentioned pattern and therefore allowing the user to use them for any given dynamodb operation.

Set up

Add the following dependency to get started:

libraryDependencies += "io.monix" %% "monix-dynamodb" % "0.1.0"

Getting started

This connector has been built on top of the DynamoDbAsyncClient since it only exposes non blocking operations, that will permit the application to be authenticated and create an channel with AWS DynamoDB service.

The DynamoDbAsyncClient needs to be defined as implicit as it will be required by the consumer and tranformer implementations.

It is also required and additional import for bringing the implicit conversions between DynamoDB requests and DynamoDbOp, the upper abstraction layer will allow to exacute them all (no need to worry about that):

import monix.connect.dynamodb.DynamoDbOp._

See below an example for transforming and consuming DynamoDb operations with monix.


//this is an example of a stream that transforms and executes DynamoDb `GetItemRequests`:
val dynamoDbRequests = List[GetItemRequest] = ???

val ob = Observable[Task[GetItemResponse]] = {
} //for each element transforms the get request operations into its respective get response 
//the resulted observable would be of type Observable[Task[GetItemResponse]]


//this is an example of a stream that consumes and executes DynamoDb `PutItemRequest`:
val putItemRequests = List[PutItemRequests] = ???

.consumeWith(DynamoDb.consumer()) //a safe and syncronous consumer that executes dynamodb requests  
//the materialized value would be of type Task[PutItemResponse]

Note that both transformers and consumer builder are generic implementations for any DynamoDbRequest, so you don't need to explicitly specify its input and output types.

Local test environment - Set up

Localstack provides a fully functional local AWS cloud stack that in this case the user can use to develop and test locally and offline the integration of the application with DynamoDB.

Add the following service description to your docker-compose.yaml file:

  image: localstack/localstack:latest
    - '4569:4569'
    - SERVICES=dynamodb

Run the following command to build, and start the dynamodb service:

docker-compose -f docker-compose.yml up -d dynamodb

Check out that the service has started correctly.

Finally create the client to connect to the local dynamodb via DynamoDbAsyncClient:

val defaultAwsCredProvider = StaticCredentialsProvider.create(AwsBasicCredentials.create("x", "x"))
implicit val client: DynamoDbAsyncClient = {
    .endpointOverride(new URI("http://localhost:4569"))

You are now ready to run your application! Note that the above example defines the client as implicit, since it is how the api will expect it.



The Hadoop Distributed File System (HDFS) is a distributed file system designed to run on commodity hardware, it is is highly fault-tolerant and it provides high throughput access which makes it suitable for applications that have to handle with large data sets.

This connector then allows to read and write hdfs files of any size in a streaming fashion.

The methods to perform these operations are exposed under the object monix.connect.hdfs.Hdfs, in which it has been built on top of the the official apache hadoop api.

Set up

Add the following dependency to get started:

libraryDependencies += "io.monix" %% "monix-hdfs" % "0.1.0"

By default the connector uses Hadoop version 3.1.1. In case you need a different one you can replace it by excluding org.apache.hadoop from monix-hdfs and add the new one to your library dependencies.

Getting started

The following import is a common requirement for all those methods defined in the Hdfs object:

import org.apache.hadoop.fs.FileSystem
//The abstract representation of a file system which could be a distributed or a local one.
import org.apache.hadoop.fs.Path
//Represents a file or directory in a FileSystem

Each use case would need different settings to create the hadoop configurations, but for testing purposes we would just need a plain one:

val conf = new Configuration() //Provides access to the hadoop configurable parameters
conf.set("", s"hdfs://localhost:$port") //especifies the local endpoint of the test hadoop minicluster
val fs: FileSystem = FileSystem.get(conf)

Then we can start interacting with hdfs, the following example shows how to construct a pipeline that reads from the specified hdfs file.

val sourcePath: Path = new Path("/source/hdfs/file_source.txt")
val chunkSize: Int = 8192 //size of the chunks to be pulled

//Once we have the hadoop classes we can create the hdfs monix reader
val ob: Observable[Array[Byte]] =, path, chunkSize)

Since using hdfs means we are dealing with big data, it makes it difficult or very expensive to read the whole file at once, therefore with the above example we will read the file in small parts configured by chunkSize that eventually will end with the whole file being processed.

Using the stream generated when reading form hdfs in the previous we could write them back into a path like:

val destinationPath: Path = new Path("/destination/hdfs/file_dest.txt")
val hdfsWriter: Consumer[Array[Byte], Task[Long]] = Hdfs.write(fs, destinationPath) 

// eventually it will return the size of the written file
val t: Task[Long] = ob.consumeWith(hdfsWriter) 

The returned type would represent the total size in bytes of the written data.

Note that the write hdfs consumer implementation provides different configurations to be passed as parameters such as enable overwrite (true by default), replication factor (3), the bufferSize (4096 bytes), blockSize (134217728 bytes =~ 128 MB) and finally a line separator which is not used by default (None).

Below example shows an example on how can them be tweaked:

val hdfsWriter: Consumer[Array[Byte], Long] = 
      path = path, 
      overwrite = false, //will fail if the path already exists
      replication = 4, 
      bufferSize = 4096,
      blockSize =  134217728, 
      lineSeparator = "\n") //each written element would include the specified line separator 

Finally, the hdfs connector also exposes an append operation, in which in this case it materializes to a Long that would represent the only the size of the appended data, but not of the whole file.

Note also that this method does not allow to configure neither the replication factor nor block size and so on, this is because these configurations are only set whenever a file is created, but an append operation would reuse them from the existing file.

See below an example:

// you would probably need to tweak the hadoop configuration to allow the append operation
conf.setBoolean("", true)
conf.set("dfs.client.block.write.replace-datanode-on-failure.policy", "NEVER") 

// note that we are re-using the `destinationPath` of the last example since should already exist
val hdfsAppender: Consumer[Array[Byte], Task[Long]] = Hdfs.append(fs, destinationPath) 
val ob: Observer[Array[Byte]] = ???
val t: Task[Long] = ob.consumeWith(hdfsAppender) 

Local environment - Set up

Apache Hadoop has a sub project called Mini Cluster that allows to locally spin up a single-node Hadoop cluster without the need to set any environment variables or manage configuration files.

Add to your library dependencies with the desired version:

"org.apache.hadoop" % "hadoop-minicluster" % "VERSION" % Test

From there on, since in this case the tests won't depend on a docker container but as per using a library dependency they will run against the JVM, so you will have to specify where to start and stop the hadoop mini cluster on the same test, it is a good practice do that on BeforeAndAfterAll:


import org.apache.hadoop.conf.Configuration
import org.apache.hadoop.fs.{FileSystem, Path}
import org.apache.hadoop.hdfs.{HdfsConfiguration, MiniDFSCluster}

private var miniHdfs: MiniDFSCluster = _
private val dir = "./temp/hadoop" //sample base dir where test data will be stored
private val port: Int = 54310 
private val conf = new Configuration()
conf.set("", s"hdfs://localhost:$port")
conf.setBoolean("", true)

override protected def beforeAll(): Unit = {
  val baseDir: File = new File(dir, "test")
  val miniDfsConf: HdfsConfiguration = new HdfsConfiguration
  miniDfsConf.set(MiniDFSCluster.HDFS_MINIDFS_BASEDIR, baseDir.getAbsolutePath)
  miniHdfs = new MiniDFSCluster.Builder(miniDfsConf)

override protected def afterAll(): Unit = {



Apache Parquet is a columnar storage format that provides the advantages of compressed, efficient data representation available to any project in the Hadoop ecosystem.

It has already been proved by multiple projects that have demonstrated the performance impact of applying the right compression and encoding scheme to the data.

Therefore, the parquet connector basically exposes stream integrations for reading and writing into and from parquet files either in the local system, hdfs or S3.

Set up

Add the following dependency:

libraryDependencies += "io.monix" %% "monix-parquet" % "0.1.0"

Getting started

These two signatures Parquet.write and are built on top of the apache parquet ParquetWriter[T] and ParquetReader[T], therefore they need an instance of these types to be passed.

The below example shows how to construct a parquet consumer that expects Protobuf messages and pushes them into the same parquet file of the specified location.

import monix.connect.parquet.Parquet
import org.apache.hadoop.fs.Path
import org.apache.parquet.avro.AvroParquetReader
import org.apache.parquet.hadoop.ParquetWriter
import org.apache.hadoop.conf.Configuration

val file: String = "/invented/file/path"
val conf = new Configuration()
val messages: List[ProtoMessage] 
val writeSupport = new ProtoWriteSupport[ProtoMessage](classOf[ProtoMessage])
val w = new ParquetWriter[ProtoMessage](new Path(file), writeSupport)
//ProtoMessage implements [[]]

On the other hand, the following code shows how to pull Avro records from a parquet file:

import monix.connect.parquet.Parquet
import org.apache.hadoop.fs.Path
import org.apache.parquet.avro.AvroParquetReader
import org.apache.parquet.hadoop.util.HadoopInputFile

val r: ParquetReader[AvroRecord] = {
  .builder[AvroRecord](HadoopInputFile.fromPath(new Path(file), conf))

val ob: Observable[AvroRecord] = Parquet.reader(r)
//AvroRecord implements [[org.apache.avro.generic.GenericRecord]]

Warning: This connector provides with the logic of building a publisher and subscriber from a given apache hadoop ParquetReader and ParquetWriter respectively, but it does not cover any existing issue within the support interoperability of the apache parquet library with external ones. Notice that p.e we have found an issue when reading parquet as protobuf messages with org.apache.parquet.hadoop.ParquetReader but not when writing. Follow the state of this issue. On the other hand, it was all fine the integration between Avro and Parquet.

Local test environment - Set up

It will depend on the specific use case, as we mentioned earlier in the introductory section it can operate on the local filesystem on hdfs or even in S3.

Therefore, depending on the application requirements, the hadoop Configuration class will need to be configured accordingly.

Local: So far in the examples has been shown how to use it locally, in which in that case it would just be needed to create a plain instance like: new org.apache.hadoop.conf.Configuration() and the local path will be specified like: new org.apache.hadoop.fs.Path("/this/represents/a/local/path").

Hdfs: On the other hand, the most common case is to work with parquet files in hdfs, in that case my recommendation is to find specific posts and examples on how to set up your configuration for that. But on some extend, for setting up the local test environment you would need to use the hadoop minicluster and set the configuration accordingly. You can check the how to do so in the monix-hdfs documentation.

S3: Finally, integrating the parequet connector with AWS S3 requires specific configuration values to be set. On behalf of configuring it to run local tests ... Note that you will also require to spin up a docker container for emulating the AWS S3 service, check how to do so in the monix-s3 documentation.



Redis is an open source, in-memory data structure store, used as a database, cache and message broker providing high availability, scalability and a outstanding performance. It supports data structures such as string, hashes, lists, sets, sorted sets with range queries, streams and more. It has a defined a set of commands to inter-operate with, and most of them are also available from the java api.

This connector has been built on top of lettuce, the most popular java library for operating with a non blocking Redis client.

Then monix-redis creates the interoperability between the reactive types returned by the lettuce api like (Mono<T> and Flux<T>) from Reactor or RedisFuture[T] At the same time that it returns the right values from scala lang and not form java, resulting in a greatly reduction of boilerplate code that makes the user to have a nice experience while integrating redis operations using monix.

See an example in below table:

Signature Lettuce Async Lettuce Reactive Monix
del RedisFuture<java.lang.Long> Mono<java.lang.Long> Task[Long]
hset RedisFuture<java.lang.Boolean> Mono<java.lang.Boolean> Task[Boolean]
hvals RedisFuture<java.utli.List> Flux<V> Observable[V]
... ... ... ...

Set up

Add the following dependency:

libraryDependencies += "io.monix" %% "monix-redis" % "0.1.0"

Getting started

Redis provides a wide range of commands to perform a different range of operations, in which it has been splitted between 15 different groups. Monix Redis connector only currently provides support for the most common used ones: (Keys, Hashes, List, Pub/Sub, Server, Sets, SortedSets, Streams and Strings). Each of these modules has its own object located under monix.connect.redis, being Redis the one that aggregates them all. But they can be individually used too.

The only extra thing you need to do for start using it is to have an implicit StatefulRedisConnection[K, V] in the scope.

On continuation let's show an example for each of the redis data group:


The following example uses the redis keys api monix.connect.redis.RedisKey to show a little example on working with some basic key operations.

//given two keys and a value
val key1: K //assuming that k1 initially exists
val key2: K //k2 does not exists
val value: String

val f: Task[Long, Boolean, Long, Long, Long, Long] = {
  for {
    initialTtl <- RedisKey.ttl(key1) //checks the ttl when it hasn't been set yet
    expire <-  RedisKey.expire(key1, 5) //sets the ttl to 5 seconds
    finalTtl <- RedisKey.ttl(key1) //checks the ttl again
    existsWithinTtl <- RedisKey.exists(key1) //checks whether k1 exists or not
    _ <- RedisKey.rename(key1, key2) //renames k1 to k2
    existsRenamed <- RedisKey.exists(key2) //checks that it exists after being renamed
    _ <- Task.sleep(6.seconds)
    existsAfterFiveSeconds <- RedisKey.exists(key2) //after 6 seconds checks ttl again
  } yield (initialTtl, expire, finalTtl, existsWithinTtl, existsRenamed, existsAfterFiveSeconds)

val (initialTtl, expire, finalTtl, existsWithinTtl, existsRenamed, existsAfterFiveSeconds).runSyncUnsafe()
initialTtl should be < 0L
finalTtl should be > 0L
expire shouldBe true
existsWithinTtl shouldBe 1L
existsRenamed shouldBe 1L
existsAfterFiveSeconds shouldBe 0L


The following example uses the redis hash api monix.connect.redis.RedisHash to insert a single element into a hash and read it back from the hash.

val key: String = ???
val field: String = ???
val value: String = ???
val t: Task[String] = for {
    _ <- RedisHash.hset(key, field, value).runSyncUnsafe() 
    v <- RedisHash.hget(key, field)
} yield v
val fv: Future[String] = t.runToFuture()


The following example uses the redis list api monix.connect.redis.RedisList to insert elements into a redis list and reading them back with limited size.

val key: String = String
val values: List[String]
val tl: Task[List[String]] = for {
  _ <- RedisList.lpush(key, values: _*)
  l <- RedisList.lrange(key, 0, values.size).toListL
} yield l
//a different alternative to use whether there is a risk of fetching a big list of elements
//or that you want to keep working with Observable[v] type rather than Task[List[V]]
val ob: Observable[String] = for {
  _ <- Observable.fromTask(RedisList.lpush(key, values: _*))
  ob <- RedisList.lrange(key, 0, values.size)
} yield ob


Example coming soon.


The following code shows how to remove all keys from all dbs in redis using the server api monix.connect.redis.RedisServer a very basic but also common use case:

val t: Task[String] = RedisServer.flushall() //returns a simple string reply


The following code uses the redis sets api from monix.connect.redis.RedisSet, this one is a bit longer than the others but not more complex.

//given three keys and two redis set of values
val k1: K 
val m1: Set[String]
val k2: K 
val m2: Set[String]
val k3: K

val f1: Future[(Long, Long, Boolean)] = {
  for {
    size1 <- RedisSet.sadd(k1, m1: _*) //first list is added to the first hey
    size2 <- RedisSet.sadd(k2, m2: _*) //second list is added to second first key
    _     <- RedisSet.sadd(k3, m1: _*) //first list is added to the third key
    moved <- RedisSet.smove(k1, k2, m1.head) //moves the head member from the first set to the second one 
  } yield { (size1, size2, moved) }
}.runToFuture() //this is not safe and only

val f2: Task[(Long, Long, List[String], List[String])] = {
  for {
    s1    <- RedisSet.smembers(k1).toListL //get members form k1
    s2    <- RedisSet.smembers(k2).toListL //get members form k2
    union <- RedisSet.sunion(k1, k2).toListL //get members form k2 and k2
    diff  <- RedisSet.sdiff(k3, k1).toListL //get the diff members between k1 and k2
  } yield (s1, s2, union, diff)

//then if the member's set did not existed before we can assume that:
val (size1, size2, moved) = f2.runSyncUnsafe()
val (s1, s2, union, diff) = f2.runSyncUnsafe()
size1 shouldBe m1.size
s1.size shouldEqual (m1.size - 1)
size2 shouldBe m2.size
s2.size shouldEqual (m2.size + 1)
moved shouldBe true
s1 shouldNot contain theSameElementsAs m1
s2 shouldNot contain theSameElementsAs m2
union should contain theSameElementsAs m1 ++ m2
//although the list are not equal as at the beginning because of the move operation, its union still is the same
diff should contain theSameElementsAs List(m1.head)
//the difference between the k3 and k1 is equal to the element that was moved


The following example uses the redis sorted sets api monix.connect.redis.RedisSortedSet to insert three scored elements into a redis sorted set, incrementing the middle one and then check that the scores are correctly reflected:

val k: String = "randomKey"
val v0: String = "v0"
val v1: String = "v1"
val v2: String = "v2"
val minScore: Double = 1
val middleScore: Double = 3 
val maxScore: Double = 4
val increment: Double = 2

RedisSortedSet.zadd(k, minScore, v0)
val t: Task[(ScoredValue[String], ScoredValue[String])] = for {
  _ <- RedisSortedSet.zadd(k, minScore, v0)
  _ <- RedisSortedSet.zadd(k, middleScore, v1)
  _ <- RedisSortedSet.zadd(k, maxScore, v2)
  _ <- RedisSortedSet.zincrby(k, increment, v1) //increments middle one by `increment` so it becomes the highest score of the set
  min <- RedisSortedSet.zpopmin(k)
  max <- RedisSortedSet.zpopmax(k) 
} yield (min, max)

//then we can assume that:
val (min, max) = t.runSyncUnsafe()
min.getScore shouldBe minScore
min.getValue shouldBe v0
max.getScore shouldBe middleScore + increment
max.getValue shouldBe v1


Example coming soon.


The following example uses the redis keys api monix.connect.redis.RedisString to insert a string into the given key and get its size from redis

val ts: Task[Long] = for {
   _ <- RedisString.set(key, value).runSyncUnsafe()
   size <- RedisString.strlen(key)
  } yield size
ts.runToFuture() //eventually will return a failure if there was a redis server error, 0 if the key did not existed or the size of the string we put 

All in one

See below a complete demonstration on how to compose a different set of Redis commands from different modules in the same for comprehension:

import monix.connect.redis.Redis
import io.lettuce.core.RedisClient
import io.lettuce.core.api.StatefulRedisConnection

val redisClient: RedisClient = RedisClient.create("redis://host:port")
implicit val connection: StatefulRedisConnection[String, String] = redisClient.connect()
val k1: K
val value: V
val k2: K
val values: List[V] 
val k3: K

val (v: String, len: Long, l: List[V], keys: List[K]) = {
  for {
    _ <- Redis.flushallAsync()            //removes all keys
    _ <- Redis.touch(k1)                  //creates the `k1`
    _ <- Redis.set(k1, value)             //insert the single `value` to `k2`
    _ <- Redis.rename(k1, k2)             //rename `k1` to `k2`
    _ <- Redis.lpush(k3, values: _*)      //push all the elements of the list to `k3`
    v <- Redis.get(k2)                    //get the element in `k2`
    _ <- Redis.lpushx(k3, v)              //pre-append v to the list in `k3`
    _ <- Redis.del(k2)                    //delete key `k2`
    len <- Redis.llen(k3)                 //lenght of the list
    l <- Redis.lrange(k3, 0, len).toListL //this is not safe unless you have a reasonable limit
    keys <- Redis.keys("*").toListL       //get all the keys
  } yield (v, len, l, keys)
}.runSyncUnsafe() // this is unsafe, and only used for testing purposes

//after this comprehnsion of redis operations it can be confirmed that:
v shouldBe value
len shouldBe values.size + 1
l should contain theSameElementsAs value :: values
keys.size shouldBe 1
keys.head shouldBe k3

Local test environment - Set up

The local tests will be use the redis docker image.

Add the following service description to your docker-compose.yaml file:

    image: redis
      - 6379:6379

Run the following command to build, and start the redis server:

docker-compose -f docker-compose.yml up -d redis

Check out that the service has started correctly.

Finally, as you might have seen in some of the examples, you can create the redis connection just by:

val redisClient: RedisClient = RedisClient.create("redis://host:port")
implicit val connection: StatefulRedisConnection[String, String] = redisClient.connect()

And now you are ready to run your application!

Note that the above example defines the client as implicit, since it is how the api will expect it.



The object storage service that offers industry leading scalability, availability, security and performance. It allows data storage of any amount of data, commonly used as a data lake for big data applications which can now be easily integrated with monix.

The module has been implemented using the S3AsyncClient since it only exposes non blocking methods. Therefore, all of the monix s3 methods defined in the S3 object would expect an implicit instance of this class to be in the scope of the call.

Set up

Add the following dependency:

libraryDependencies += "io.monix" %% "monix-s3" % "0.1.0"

Getting started

First thing is to create the s3 client that will allow us to authenticate and create an channel between our application and the AWS S3 service.

So the below code shows an example on how to set up this connection. Note that in this case the authentication is done thorugh AWS S3 using access and secret keys, but you might use another method such as IAM roles.

import{AwsBasicCredentials, StaticCredentialsProvider}

val basicAWSCredentials: AwsBasicCredentials = AwsBasicCredentials.create(s3AccessKey, s3SecretKey)
val credentialsProvider: StaticCredentialsProvider = StaticCredentialsProvider.create(basicAWSCredentials)

// Note that the client is defined as implicit, this is on purpose since each of the methods defined in
// the monix s3 connector will expect that.
implicit val s3Client: S3AsyncClient = S3AsyncClient
   .endpointOverride(URI.create(endPoint))//this one is used to point to the localhost s3 service, not used in prod 

Once we have configured the s3 client, let's start with the basic operations to create and delete buckets:

import{CreateBucketResponse, DeleteBucketResponse}

val bucketName: String = "myBucket" 
val _: Task[CreateBucketResponse] = S3.createBucket(bucketName)
val _: Task[DeleteBucketResponse] = S3.deleteBucket(bucketName)

You can also operate at object level within a bucket with:

import{DeleteObjectResponse, ListObjectsResponse}

val bucketName: String = "myBucket" 
val _: Task[DeleteObjectResponse] = S3.deleteObject(bucketName)
val _: Task[ListObjectsResponse] = S3.listObjects(bucketName)

On the other hand, to get and put objects:


val bucketName: String = "myBucket" 

//get example
val objectKey: String = "/object/file.txt"
val _: Task[Array[Byte]] = S3.getObject(bucketName, objectKey)

//put object example
val content: Array[Byte] = "file content".getBytes()
val _: Task[PutObjectResponse] = S3.putObject(bucketName, objectKey, content)

Finally, for dealing with large files of data you might want to use the multipartUpload consumer. This one consumes an observable and synchronously makes partial uploads of the incoming chunks.

Thus, it reduces substantially the risk on having jvm overhead errors or getting http requests failures, since the whole file does not need to be allocated in the memory and the http request body won't be that big.

The partial uploads can be fine tuned by the minimum chunksize that will be sent, being 5MB the default minimum size (equally as an integer value of 5242880).


// given an strem of chunks (Array[Byte]) 
val ob: Observable[Array[Byte]] = Observable.fromIterable(chunks)

// and a multipart upload consumer
val multipartUploadConsumer: Consumer[Array[Byte], Task[CompleteMultipartUploadResponse]] =
  S3.multipartUpload(bucketName, objectKey)

// then

Local test environment - Set up

For AWS S3 local testing we went with minio instead of localstack, since we found an issue that can block you on writing your functional tests.

Add the following service description to your docker-compose.yaml file:

  image: minio/minio
    - "9000:9000"
    - ./minio/data:/data
    test: ["CMD", "curl", "-f", "http://localhost:9000/minio/health/live"]
    interval: 35s
    timeout: 20s
    retries: 3
  command: server --compat /data

Run the following command to build, and start the redis server:

docker-compose -f docker-compose.yml up -d minio

Check out that the service has started correctly, notice that a healthcheck has been defined on the description of the minio service, that's because minio s3 is a very heavy image and sometimes it takes too long to be set up or sometime it even fails, so that would prevent those cases.

Finally, create the connection with AWS S3, note that minio does not has support for AnonymousCredentialsProvider, therefore you'll have to use AwsBasicCredentials, in which the key and secret will correspond respectively to the defined environment variables from docker compose definition MINIO_ACCESS_KEY and MINIO_SECRET_KEY.

import{AwsBasicCredentials, StaticCredentialsProvider}

val minioEndPoint: String = "http://localhost:9000"

val s3AccessKey: String = "TESTKEY" //see docker minio env var `MINIO_ACCESS_KEY`
val s3SecretKey: String = "TESTSECRET" //see docker minio env var `MINIO_SECRET_KEY`

val basicAWSCredentials = AwsBasicCredentials.create(s3AccessKey, s3SecretKey)
implicit val s3AsyncClient: S3AsyncClient = S3AsyncClient

Now you are ready to run your application!

Note that the above example defines the client as implicit, since it is how the api will expect this one.


The Monix Connect project welcomes contributions from anybody wishing to participate. All code or documentation that is provided must be licensed with the same license that Monix Connect is licensed with (Apache 2.0, see LICENSE.txt).

People are expected to follow the Scala Code of Conduct when discussing Monix on GitHub, Gitter channel, or other venues.

Feel free to open an issue if you notice a bug, you have a question about the code, an idea for an existing connector or even for adding a new one. Pull requests are also gladly accepted. For more information, check out the contributor guide.


All code in this repository is licensed under the Apache License, Version 2.0. See LICENCE.txt.