So I thought that it might be a great idea to run an RT kernel inside Kata containers. This is a usecase because I soon hope to see Kata containers running on real-time capable hypervisors and also being used in scenarios where real-time is a thing. Soon!

For now, let’s look at how I went about doing what I did..

  1. You need to go get github.com/kata-containers/packaging repository. (or, git clone if you so prefer.) Be sure to have your $GOPATH properly set!!
  2. cd into packaging/kernel directory.
  3. I chose the 4.19.31 version of the kernel. Primarily because it was a newer kernel (not too different from the kernel version that comes with the current kata release.) and because it had the RT patches available
  4. I changed the kernel_version="" line to kernel_version="4.19.31"

That’s it. We are ready to (1) apply the necessary patches from Kata maintainers to our Kernel of choosing and (2) apply the RT patches:

# download and apply the kata patches to the kernel
./build-kernel.sh setup

cd kata-linux-4.19.31-36
patch -p1<../path-to-extracted-patch/patch-4.19.31-rt18.patch

Wait… we need to first, make menuconfig and enable RT capabilities

General Setup 
  --> Preemption Model
    --> Fully Preemptible Kernel (RT)

Now, we’re ready to build the Kernel and install it*:

./build-kernel.sh setup
sudo ./build-kernel.sh install

Drum Roll please

$ docker run -it --runtime kata-runtime ubuntu bash
root@77cf04fd8290:/# uname -r
4.19.31-rt18
root@77cf04fd8290:/# uname -a
Linux 77cf04fd8290 4.19.31-rt18 #2 SMP PREEMPT RT Mon Apr 29 09:06:08 CEST 2019 x86_64 x86_64 x86_64 GNU/Linux
root@77cf04fd8290:/#

So proud!!!

Happy Building!!

Note on Kernel Files

vmlinux: uncompressed kernel. | vmlinuz: compressed kernel. | bzImage: located under arch/x86_64/boot/bzImage. Big Zimage. Compressed kernel image.

More info: https://stackoverflow.com/a/22338835/3760442

Acknowledgements

Special thanks to @egernst, @rico and the great team on Slack!! Though this was my first foray into Kata Containers, I must say the folks were very welcoming. Thank you all!!

* I built the kernel (as of the time of writing) using make build -j4 instead of using the build-kernel.sh script but it shouldn’t matter. Just FYI.