I just spent a day on a wild goose chase trying to figure out what was causing this error:

ALPN is not configured properly. See https://github.com/grpc/grpc-java/blob/master/SECURITY.md#troubleshooting for more information.

Reading that page, and looking at my Maven dependency tree, I thought I had some kind of version conflict. I spent a day uselessly swapping out different library versions to try and fix this. In frustration I created a completely new project, with the same dependencies, and it worked. I turns out my app is using the Java Security Manager, and it was silently blocking tcnative from being loaded by netty-tcnative-boringssl-static.

Adding these three permissions fixed it:

permissions.add(new NetPermission("getProxySelector", "read"));
permissions.add(new FilePermission(System.getProperty("java.io.tmpdir")+"/-", "read,write"));
permissions.add(new RuntimePermission("loadLibrary.*"));

I couldn't figure out how to whitelist only the tcnative library, as the Netty Native Library Loader appends a random number to the library name every time (ironically, probably for security reasons).