Akka Stream 2.0-M1: Quick Update

Yesterday was announced the first milestone of the second version of Akka Stream and Http. I wanted to give it a try so I updated the previous project in order to work with this new version. You’ll find a new branch called “akka-stream-2.0-M1”.


Functions partial and closed of FlowGraph are no longer existing. They were replaced by function create. As you can see for instance in EventInputFlow the change is very straight forward in partial cases.

One of the most significant changes I had to do was in the FlowTestKit where I was using FlowGraph.closed. And as I pointed above it was replaced by the function create. But in this case it’s mandatory to return a ClosedShape. With this new object it’s not possible to invoke the run() function because it’s not runnable like previously. To make it runnable it’s necessary to use RunnableGraph.fromGraph(closedShape) and then you can invoke the run() function.

All the changes introduced in the project can be seen in this comparison with the master branch.


Another big change that I’m not using in the demo project is the wrap() function. It was replaced by descriptive functions depending on the case. If you want to create a Flow from a FlowShape you should use Flow.fromGraph but if you need to create a Flow from a Sink and Source you should use now the function Flow.fromSinkAndSource  or Flow.fromSinkAndSourceMat.

If you were using FlexiMerge and FlexiRoute for custom stream processing you’ll notice that they have been replaced by GraphStage. Take a look at the migration guide from 1.0 to 2.x to see all the changes introduced in this first milestone and if you can give it a try!


It’s promising what is coming in this new Akka Stream 2 world. The API is becoming stronger, powerful and very handy. And talking about performance it’s worth to mention that the stream processing is faster now and it will be much faster in the upcoming versions – with the introduction of GraphStage it will be possible to execute multiple stream processing steps inside one actor, reducing the numbers of thread-hops -. Other libraries such as Akka Http are getting improvements too thanks to Akka Stream joint efforts.

Until next post!


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