Vert.x GraalVM - Native Image Test

This is a basic test project which uses GraalVM / Substrate VM VM to build a native image of a Vert.x Web application.

How to build

I prepared and tested the build only on Linux but it should also work on other platforms.

1. Build a shaded jar of your application
2. Run the native-image tool from GraalVM to generate the executable

The build.sh file contains more details about needed arguments.

Patches

In this test project I patched a few Vert.x and Netty classes to avoid imports related to native transports and SSL. Otherwise the image could not be build.

Vert.x Transport

First I needed to patch the io.vertx.core.net.impl.transport.Transport class in order to prevent the loading of EPoll and KQueue native support. Otherwise Substrate VM will try to load these classes and fail.

public class Transport {
…
  /**
   * The native transport, it may be {@code null} or failed.
   */
  public static Transport nativeTransport() {
    // Patched: I remove the native transport discovery. 
    // The imports would be picked up by substrate 
    // and cause further issues. 
    return null;
  }
…
}

Netty SSL

Native SSL support is another problematic area. I created a patched dummy io.netty.handler.ssl.ReferenceCountedOpenSslEngine class in order to prevent Substrate VM from digging deeper into the SSL code of Netty.

Netty Reflections

Next we need to set up the reflection configuration within reflectconfigs/netty.json.

Netty uses reflection to instantiate the socket channels. This is done in the ReflectiveChannelFactory. We need to tell Substrate VM how classes of type NioServerSocketChannel and NioSocketChannel can be instantiated.

[
  {
    "name" : "io.netty.channel.socket.nio.NioSocketChannel",
    "methods" : [
      { "name" : "<init>", "parameterTypes" : [] }
    ]
  },
  {
    "name" : "io.netty.channel.socket.nio.NioServerSocketChannel",
    "methods" : [
      { "name" : "<init>", "parameterTypes" : [] }
    ]
  }
]

Limitations

Native EPoll, KQueue support, SSL is not yet working.

Related issue: oracle/graal#353

Blog post

More information can also be found in my post on the Vert.x blog.