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Manage WasmEdge apps in CRI-O

Quick start

You can use the install.sh script to install CRI-O and crun on Ubuntu 20.04.

wget -qO- https://raw.githubusercontent.com/second-state/wasmedge-containers-examples/main/crio/install.sh | bash

The simple_wasi_application.sh script shows how to pull a WebAssembly application from Docker Hub, and then run it as a containerized application in CRI-O.

wget -qO- https://raw.githubusercontent.com/second-state/wasmedge-containers-examples/main/crio/simple_wasi_application.sh | bash

You should see results from the WebAssembly program printed in the console log. Here is an example.

The sections below are step-by-step instructions for the above demo.

Install WasmEdge

Use the simple install script to install WasmEdge.

wget -qO- https://raw.githubusercontent.com/WasmEdge/WasmEdge/master/utils/install.sh | bash -s -- -p /usr/local

Build and install crun

You need a crun binary that supports WasmEdge. For now, the easiest approach is just built it yourself from source. First, let's make sure that crun dependencies are installed on your Ubuntu 20.04. For other Linux distributions, please see here.

sudo apt update
sudo apt install -y make git gcc build-essential pkgconf libtool \
   libsystemd-dev libprotobuf-c-dev libcap-dev libseccomp-dev libyajl-dev \
   go-md2man libtool autoconf python3 automake

Next, configure, build, and install a crun binary with WasmEdge support.

git clone https://github.com/containers/crun
cd crun
./autogen.sh
./configure --with-wasmedge
make
sudo make install

Install CRI-O

Use the following commands to install CRI-O on your system.

export OS="xUbuntu_20.04"
export VERSION="1.21"
apt update
apt install -y libseccomp2 || sudo apt update -y libseccomp2
echo "deb https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/$OS/ /" > /etc/apt/sources.list.d/devel:kubic:libcontainers:stable.list
echo "deb https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable:/cri-o:/$VERSION/$OS/ /" > /etc/apt/sources.list.d/devel:kubic:libcontainers:stable:cri-o:$VERSION.list

curl -L https://download.opensuse.org/repositories/devel:kubic:libcontainers:stable:cri-o:$VERSION/$OS/Release.key | apt-key add -
curl -L https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/$OS/Release.key | apt-key add -

apt-get update
apt-get install criu libyajl2
apt-get install cri-o cri-o-runc cri-tools containernetworking-plugins
systemctl start crio

Configure CRI-O

CRI-O uses the runc runtime by default and we need to configure it to use crun instead. That is done by adding to two configuration files.

First, create a /etc/crio/crio.conf file and add the following lines as its content. It tells CRI-O to use crun by default.

[crio.runtime]
default_runtime = "crun"

The crun runtime is in turn defined in the /etc/crio/crio.conf.d/01-crio-runc.conf file.

[crio.runtime.runtimes.runc]
runtime_path = "/usr/lib/cri-o-runc/sbin/runc"
runtime_type = "oci"
runtime_root = "/run/runc"
# The above is the original content

# Add our crunw runtime here
[crio.runtime.runtimes.crun]
runtime_path = "/usr/bin/crun"
runtime_type = "oci"
runtime_root = "/run/crun"

Next, restart CRI-O to apply the configuration changes.

systemctl restart crio

Run a simple WebAssembly app

Finally, we can run a simple WebAssembly program using CRI-O. A seperate article explains how to compile, package, and publish the WebAssembly program as a container image to Docker hub. In this section, we will start off pulling this WebAssembly-based container image from Docker hub using CRI-O tools.

crictl pull docker.io/wasmedge/example-wasi:latest

Next, we need to create two simple configuration files that specifies how CRI-O should run this WebAssembly image in a sandbox. We already have those two files container_wasi.json and sandbox_config.json. You can just download them to your local directory as follows.

wget https://raw.githubusercontent.com/second-state/wasmedge-containers-examples/main/crio/sandbox_config.json
wget https://raw.githubusercontent.com/second-state/wasmedge-containers-examples/main/crio/container_wasi.json

Now you can use CRI-O to create a pod and a container using the specified configurations.

# Create the POD. Output will be different from example.
sudo crictl runp sandbox_config.json
7992e75df00cc1cf4bff8bff660718139e3ad973c7180baceb9c84d074b516a4
# Set a helper variable for later use.
POD_ID=7992e75df00cc1cf4bff8bff660718139e3ad973c7180baceb9c84d074b516a4

# Create the container instance. Output will be different from example.
sudo crictl create $POD_ID container_wasi.json sandbox_config.json
1d056e4a8a168f0c76af122d42c98510670255b16242e81f8e8bce8bd3a4476f

Starting the container would execute the WebAssembly program. You can see the output in the console.

# List the container, the state should be `Created`
sudo crictl ps -a

CONTAINER           IMAGE                                          CREATED              STATE               NAME                     ATTEMPT             POD ID
1d056e4a8a168       wasmedge/example-wasi:latest                   About a minute ago   Created             podsandbox1-wasm-wasi   0                   7992e75df00cc

# Start the container
sudo crictl start 1d056e4a8a168f0c76af122d42c98510670255b16242e81f8e8bce8bd3a4476f
1d056e4a8a168f0c76af122d42c98510670255b16242e81f8e8bce8bd3a4476f

# Check the container status again.
# If the container is not finishing its job, you will see the Running state
# Because this example is very tiny. You may see Exited at this moment.
sudo crictl ps -a
CONTAINER           IMAGE                                          CREATED              STATE               NAME                     ATTEMPT             POD ID
1d056e4a8a168       wasmedge/example-wasi:latest                   About a minute ago   Running             podsandbox1-wasm-wasi   0                   7992e75df00cc

# When the container is finished. You can see the state becomes Exited.
sudo crictl ps -a
CONTAINER           IMAGE                                          CREATED              STATE               NAME                     ATTEMPT             POD ID
1d056e4a8a168       wasmedge/example-wasi:latest                   About a minute ago   Exited              podsandbox1-wasm-wasi   0                   7992e75df00cc

# Check the container's logs
sudo crictl logs 1d056e4a8a168f0c76af122d42c98510670255b16242e81f8e8bce8bd3a4476f

Test 1: Print Random Number
Random number: 960251471

Test 2: Print Random Bytes
Random bytes: [50, 222, 62, 128, 120, 26, 64, 42, 210, 137, 176, 90, 60, 24, 183, 56, 150, 35, 209, 211, 141, 146, 2, 61, 215, 167, 194, 1, 15, 44, 156, 27, 179, 23, 241, 138, 71, 32, 173, 159, 180, 21, 198, 197, 247, 80, 35, 75, 245, 31, 6, 246, 23, 54, 9, 192, 3, 103, 72, 186, 39, 182, 248, 80, 146, 70, 244, 28, 166, 197, 17, 42, 109, 245, 83, 35, 106, 130, 233, 143, 90, 78, 155, 29, 230, 34, 58, 49, 234, 230, 145, 119, 83, 44, 111, 57, 164, 82, 120, 183, 194, 201, 133, 106, 3, 73, 164, 155, 224, 218, 73, 31, 54, 28, 124, 2, 38, 253, 114, 222, 217, 202, 59, 138, 155, 71, 178, 113]

Test 3: Call an echo function
Printed from wasi: This is from a main function
This is from a main function

Test 4: Print Environment Variables
The env vars are as follows.
PATH: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
TERM: xterm
HOSTNAME: crictl_host
PATH: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
The args are as follows.
/var/lib/containers/storage/overlay/006e7cf16e82dc7052994232c436991f429109edea14a8437e74f601b5ee1e83/merged/wasi_example_main.wasm
50000000

Test 5: Create a file `/tmp.txt` with content `This is in a file`

Test 6: Read the content from the previous file
File content is This is in a file

Test 7: Delete the previous file

That's it!