Build a Nabla Docker Image

In this post, we go through the basic steps for containerizing a unikernel application and running it on nabla runnc. Checkout nabla containers and in particular runnc.

How to

In order to build a docker image for nabla containers, we have to build:

• the nabla toolstack
• the unikernel image
• the docker image

Build the nabla toolstack

There’s an informative blog post on how to build the nabla rumprun toolstack here. Now that our aarch64 changes are upstream, the process should be as easy as the following:

git clone https://github.com/nabla-containers/rumrpun
cd rumprun
git submodule update --init
make
. obj/config-PATH.sh

and you should end up with the toolstack (${ARCH}-rumprun-netbsd-) in your PATH variable.

Alternatively you can use one of the (unofficial) docker images with the toolstack embedded at /usr/local:

• x86_64-rumprun-netbsd-
• aarch64-rumprun-netbsd-

You can run these containers using the following command:

docker run --runtime=runc --rm -v ${PWD}:/build -it cloudkernels/debian-rumprun-build:${ARCH} /bin/bash

where ${ARCH} could be x86_64 or aarch64.

Build the unikernel Image

building the image is as easy as running the following:

${ARCH}-rumprun-netbsd-gcc myprog.c -o myprog-rumprun

rumprun-bake solo5-spt myprog.spt myprog-rumprun

So we have ourselves an .spt file (a unikernel). To try it out, assuming you have a solo5-spt binary lying around you can do the following:

solo5-spt ./myprog.spt

Assuming the unikernel image is successful, its time to construct the docker image.

Build the docker image

Rumprun is a quirky unikernel framework, with a number of assumptions we can’t ignore. Thus, in order to get the unikernel running correctly when in a nabla container environment, we need to be careful and include the correct stubs for a dummy root filesystem. So, clone this repo, which contains the basic rootfs from rumprun’s lib/librumprunfs_base/rootfs, and a template Dockerfile shown below:

FROM scratch
COPY myprog.spt /myprog.nabla
COPY rootfs/etc /etc
ENTRYPOINT [ "myprog.nabla" ]

Copy the spt file in this directory and run:

docker build -f Dockerfile -t myprog-nabla:${ARCH} .

You should end up with a local docker image named myprog-nabla, tagged with your current architecture variant (x86_64 or aarch64).

Assuming you have setup runnc correctly, spawning the container is as easy as:

docker run --rm --runtime=runnc myprog-nabla:${ARCH}