I need to make a call that might take a few seconds. What is the best way to do this?

Create a background thread in do_before_launch or do_launch to do the work. Use on_timer to poll until the result is available.

I don't see the header files in the .zip file. Where are they?

The SDK headers are baked into the docker image along with the build tools. Once you've loaded the image with docker load < spark_sdk.img you can run this command to copy them out to your local file system docker run --rm -it -v $PWD:/out spark_sdk /bin/tar -cvf /out/headers.tar /sdk/include This will copy the headers to the current directory in headers.tar. We still recommend doing the actual build inside the docker environment but having a copy of the headers can be useful for setting up your development environment.