Running web assembly in containers

Install wasm runtime
Compile crun with wasm support
Compile a wasm example application
Build a wasm container
Running a wasm container

In our recent blog post on Web Assembly we highlighted the implementation of WASM support into the crun Open Container Initiative (OCI) runtime. This change paves the way for Podman and OpenShift to run WASM workloads alongside our traditional container workloads.

This demo will step through how WASM modules can be run alongside traditional workloads in Podman.

Install wasm runtime

Our first pre-requisite step is to ensure our machine has a WASM runtime installed. For this demo we will use WasmEdge.

Run the code block below to install WasmEdge into the /usr/local/ dir using the project install script.

# Install via script
curl -sSf https://raw.githubusercontent.com/WasmEdge/WasmEdge/master/utils/install.sh | sudo bash -s -- -p /usr/local

# Verify installed version
wasmedge --version

Compile crun with wasm support

Once wasmedge is available we then need to ensure we have a version of crun available that has support for WASM. In my case I needed to download and compile a newer release including the --with-wasmedge compile flag.

We need to start with installing compile dependencies, these are listed here in the official docs.

sudo apt-get install --yes make git gcc build-essential pkgconf libtool libsystemd-dev libprotobuf-c-dev libcap-dev libseccomp-dev libyajl-dev libgcrypt20-dev go-md2man autoconf python3 automake

Once the required dependencies are present on our system we can clone down the source and compile it with the additional wasmedge flag.

# Clone the crun source
git clone https://github.com/containers/crun && cd crun

# Compile with wasm flag
./autogen.sh
./configure --with-wasmedge
make
sudo make install && cd ../ && rm -rf crun

If everything worked correctly we can see the +WASM:wasmedge flag in our crun version information:

crun --version

The output should look something like the example below:

crun version 1.7.2.0.0.0.80-940b
commit: 940bf973f144c81149cf05135f127ca6f0d19eb6
rundir: /run/user/1000/crun
spec: 1.0.0
+SYSTEMD +SELINUX +APPARMOR +CAP +SECCOMP +EBPF +WASM:wasmedge +YAJL

Compile a wasm example application

With our system setup let's compile a hello world in rust to .wasm so we can then run it with our container engine.

# Create new rust project
rm -rf hello_wasm && cargo new hello_wasm --bin && cd hello_wasm

# Customise the main function
sed -i 's/world/openshift meetup/g' src/main.rs
cat src/main.rs

# Ensure we have rust wasm tooling installed
rustup target add wasm32-wasi

# Compile to the wasm target
cargo build --target wasm32-wasi

We can run it directly with our wasmedge runtime to verify everything worked.

wasmedge target/wasm32-wasi/debug/hello_wasm.wasm

Build a wasm container

Awesome, we have a compiled .wasm portable binary. Lets build this into an OCI compliant image so that our container engine can run it like a traditional container.

# Review contents of included containerfile
cd ../ && cat Containerfile

# Build the container with buildah
buildah build --annotation "module.wasm.image/variant=compat" -t mywasm-image .

The interesting thing about wasm container images is just how small they can potentially be as the image doesn't contain any operating system or libraries, literally just our portable .wasm file.

If we take a look at the image we just built it's only a couple of megabytes!

podman images | grep wasm

Running a wasm container

Now that we have a container image built let's run it with Podman.

Note that we need to ensure Podman is pointing at our customised container runtime that has WASM support, this can be done via either configuration file or cli parameter.

podman --runtime /usr/local/bin/crun run -t --rm localhost/mywasm-image:latest

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