Apache Pekko gRPC

Support for building streaming gRPC servers and clients on top of Apache Pekko Streams.

This library is meant to be used as a building block in projects using the Pekko toolkit.


Project Status

This library is ready to be used in production, but API's and build system plugins are still expected to be improved and may change.

The API on both sides (Client and Server) is a simple Pekko Streams-based one.

The client side is currently implemented on top of io.grpc:grpc-netty-shaded, we plan to replace this by just io.grpc:grpc-core and Pekko HTTP.

As for performance, we are currently relying on the JVM TLS implementation, which is sufficient for many use cases, but is planned to be replaced with conscrypt or netty-tcnative.

General overview

gRPC is a schema-first RPC framework, where your protocol is declared in a protobuf definition, and requests and responses will be streamed over an HTTP/2 connection.

Based on a protobuf service definition, pekko-grpc can generate:

  • Model classes (using plain protoc for Java or scalapb for Scala)
  • The API (as an interface for Java or a trait for Scala), expressed in Pekko Streams Sources
  • On the server side, code to create a Pekko HTTP route based on your implementation of the API
  • On the client side, a client for the API.

Project structure

The project is split up in a number of subprojects:

  • codegen: code generation shared among plugins
  • runtime: run-time utilities used by the generated code
  • sbt-plugin: the sbt plugin
  • scalapb-protoc-plugin: the scalapb Scala model code generation packaged as a protoc plugin, to be used from gradle
  • interop-tests

Additionally, 'plugin-tester-java' and 'plugin-tester-scala' contain an example project in Java and Scala respectively, with both sbt and Gradle configurations.

Compatibility & support

If used with JDK 8 prior to version 1.8.0_251 you must add an ALPN agent. See the note in the Akka HTTP docs.

Building from Source


  • Make sure you have installed a Java Development Kit (JDK) version 8 or later.
  • Make sure you have sbt installed.
  • Maven is needed for tasks related to building and testing Maven plugin support.
  • Gradle is needed for tasks related to building and testing Gradle plugin support. We have gradlew scripts that will install the right version of Gradle and run the gradle tasks using it.
  • Graphviz is needed for the scaladoc generation build task, which is part of the release.

Running the Build

  • Open a command window and change directory to your preferred base directory
  • Use git to clone the repo or download a source release from https://pekko.apache.org (and unzip or untar it, as appropriate)
  • Change directory to the directory where you installed the source (you should have a file called build.sbt in this directory)
  • sbt compile compiles the main source for project default version of Scala (2.12)
    • sbt +compile will compile for all supported versions of Scala
  • sbt test will compile the code and run the unit tests
  • sbt testQuick similar to test but when repeated in shell mode will only run failing tests
  • sbt package will build the jars
    • the jars will built into target dirs of the various modules
    • for the the 'runtime' module, the jar will be built to runtime/target/scala-2.12/
  • sbt publishLocal will push the jars to your local Apache Ivy repository
  • sbt publishM2 will push the jars to your local Apache Maven repository
  • sbt docs/paradox will build the docs (the ones describing the module features)
    • sbt docs/paradoxBrowse does the same but will open the docs in your browser when complete
    • the index.html file will appear in target/paradox/site/main/
  • sbt unidoc will build the Javadocs for all the modules and load them to one place (may require Graphviz, see Prerequisites above)
    • the index.html file will appear in target/scala-2.13/unidoc/
  • sbt sourceDistGenerate will generate source release to target/dist/
  • The version number that appears in filenames and docs is derived, by default. The derived version contains the most git commit id or the date/time (if the directory is not under git control).
    • You can set the version number explicitly when running sbt commands
      • eg sbt "set ThisBuild / version := \"1.0.0\"; sourceDistGenerate"
    • Or you can add a file called version.sbt to the same directory that has the build.sbt containing something like
      • ThisBuild / version := "1.0.0"

Maven plugin

  • the Maven plugin is built using sbt
  • Build the Maven plugin and not its version number because the tests need the version number
  • You can test the Maven plugin by changing directory into the plugin-tester-java dir
    • mvn -Dpekko.grpc.project.version=<version> pekko-grpc:generate compile
  • You can run the equivalent Scala tests by changing directory into the plugin-tester-scala dir
    • mvn -Dpekko.grpc.project.version=<version> pekko-grpc:generate scala:compile

Gradle plugin

  • the Gradle plugin is built using gradle
  • The gradle plugin will automatically derive the version of the artifact from sbt.
    • In other words sbt is the source of truth when it comes to deriving the version
  • You can test the Gradle plugin by change directory into the plugin-tester-java dir
    • ./gradlew clean test -Dpekko.grpc.project.version=<version>
  • You can run the equivalent Scala tests by changing directory into the plugin-tester-scala dir
    • ./gradlew clean test -Dpekko.grpc.project.version=<version>


Pekko gRPC is Open Source and available under the Apache 2 License.