Blog Posts

Akka Streams is a powerful implementation on top of the Reactive Streams SPI for non-blocking asynchronous communication with back-pressure on the JVM. This post is not about explaining what this means, nor what Akka Streams does. The purpose of this post is to explain what on earth the NotUsed type in type signatures of Akka Streams is all about which ... Read More

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Tags: #akka #it

Akka anti-patterns: blocking
15.05.2017 07:59 by Manuel

This is probably one of the most frequent (and dangerous) anti-patterns when it comes to working with Akka. Let’s look at an adequate description of the mindset you must be in in order to use it: So maybe you didn’t actually want to see the world burn. Maybe you thought that this one time it was okay to call blocking ... Read More

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Choosing Akka as a tool is often – if not always – driven by the need for good performance. Surely, the actor model itself is appealing as a means for organizing and reasoning about code, but this isn’t in itself a good reason enough to use the Akka toolkit. If all you are concerned about is a nice way to ... Read More

The post Akka anti-patterns: being out of touch with the hardware appeared first on manuel bernhardt.

Update: removed rogue toString call in the second code example, since it was unnecessary (and harmful). Debugging actor systems is no small feat, even when there is IDE support for it. In fact, debugging any asynchronous system for that matter is a rather complicated task. Which is why, especially during development, it is not entirely uncommon to rely on DEBUG ... Read More

The post Akka anti-patterns: logging (the wrong way) appeared first on manuel bernhardt.

Admittedly I’ve seen this one in use only one time, but it was one time too many. For some reason I keep seeing clients come up with this during design discussions and reviews though, therefore it makes it into the list of Akka anti-patterns. What I am talking about is this: Reasons I hear for this design: isolation of concerns: ... Read More

The post Akka anti-patterns: too many actor systems appeared first on manuel bernhardt.

The actor model makes it possible to build highly-concurrent applications through the notion that actors obey the actor send rule and the actor subsequent processing rule, hence creating a single-threaded environment inside of an actor. That being said, it’s all an illusion: as we have briefly talked about previously, Akka’s dispatchers make sure that messages are being processed by actors ... Read More

The post Akka anti-patterns: race conditions appeared first on manuel bernhardt.

One of the fundamental ideas built into Akka is the one of failure handling through parental supervision. In other words this means agencing actors in such a way that parent actors that depend upon the correct execution of a child to perform their work are also responsible for deciding what to do when one of the child actor crashes. An ... Read More

The post Akka anti-patterns: flat actor hierarchies or mixing business logic and failure handling appeared first on manuel bernhardt.

When I work with clients on designing actor systems there are a few anti-patterns that seem to make it into initial, non-reviewed designs no matter what. In this series of short articles I would like to cover a few of those. Anti-pattern #1: sharing mutable state accross actors Even though the Akka documentation points this out in various places, one ... Read More

The post Akka anti-patterns: shared mutable state appeared first on manuel bernhardt.

When you need to build your Scala project, but have no way to install SBT on your host, you can still do it if you have Docker.

There are few ready to use container images on DockerHub. We create our own.

All we need for that is to prepare a Dockerfile:

 FROM java:latest  
MAINTAINER Nikolay Kushin
ENV SBT_OPTS -Xmx2G -XX:+UseConcMarkSweepGC -XX:+CMSClassUnloadingEnabled -Xss2M -Duser.timezone=GMT
# install sbt
RUN dpkg -i sbt-$SBT_VERSION.deb
# install scala
RUN dpkg -i scala-$SCALA_VERSION.deb
# fetch base dependencies
RUN sbt compile
CMD ["sbt"]

Our Dockerfile is relatively easy and self-explaining.

Next step is to build an image. Save Dockerfile in some folder and execute following commande in terminal:

 docker build -t sbt-docker .  

Now when the image is ready we can create container with mounted source folder, containing our Scala project and run SBT.

 docker run -it --rm -v $(pwd):/src sbt-docker sbt docker:stage  

Thats it! Enjoy!
Simply run following script to install latest Scala and SBT on your Ubuntu: