# Kata Containers with ACRN

This document provides an overview on how to run Kata containers with ACRN hypervisor and device model.

## Introduction

ACRN is a flexible, lightweight Type-1 reference hypervisor built with real-time and safety-criticality in mind. ACRN uses an open source platform making it optimized to streamline embedded development.

Some of the key features being:

- Small footprint - Approx. 25K lines of code (LOC).
- Real Time - Low latency, faster boot time, improves overall responsiveness with hardware.
- Adaptability - Multi-OS support for guest operating systems like Linux, Android, RTOSes.
- Rich I/O mediators - Allows sharing of various I/O devices across VMs.
- Optimized for a variety of IoT (Internet of Things) and embedded device solutions.

Please refer to ACRN [documentation](https://projectacrn.github.io/latest/index.html) for more details on ACRN hypervisor and device model.

## Pre-requisites

This document requires the presence of the ACRN hypervisor and Kata Containers on your system. Install using the instructions available through the following links:

- ACRN supported [Hardware](https://projectacrn.github.io/latest/hardware.html#supported-hardware).
  > **Note:** Please make sure to have a minimum of 4 logical processors (HT) or cores.
- ACRN [software](https://projectacrn.github.io/latest/tutorials/run_kata_containers.html) setup.
- For networking, ACRN supports either MACVTAP or TAP. If MACVTAP is not enabled in the Service OS, please follow the below steps to update the kernel:

  ```sh
   $ git clone https://github.com/projectacrn/acrn-kernel.git
   $ cd acrn-kernel
   $ cp kernel_config_sos .config
   $ sed -i "s/# CONFIG_MACVLAN is not set/CONFIG_MACVLAN=y/" .config
   $ sed -i '$ i CONFIG_MACVTAP=y' .config
   $ make clean && make olddefconfig && make && sudo make modules_install INSTALL_MOD_PATH=out/
  ```
  Login into Service OS and update the kernel with MACVTAP support:

  ```sh
  $ sudo mount /dev/sda1 /mnt
  $ sudo scp -r <user name>@<host address>:<your workspace>/acrn-kernel/arch/x86/boot/bzImage /mnt/EFI/org.clearlinux/
  $ sudo scp -r <user name>@<host address>:<your workspace>/acrn-kernel/out/lib/modules/* /lib/modules/
  $ conf_file=$(sed -n '$ s/default //p' /mnt/loader/loader.conf).conf
  $ kernel_img=$(sed -n 2p /mnt/loader/entries/$conf_file | cut -d'/' -f4)
  $ sudo sed -i "s/$kernel_img/bzImage/g" /mnt/loader/entries/$conf_file
  $ sync && sudo umount /mnt && sudo reboot
  ```
- Kata Containers installation: Automated installation does not seem to be supported for Clear Linux, so please use [manual installation](../Developer-Guide.md) steps.

> **Note:** Create rootfs image and not initrd image.

In order to run Kata with ACRN, your container stack must provide block-based storage, such as device-mapper.

> **Note:** Currently, by design you can only launch one VM from Kata Containers using ACRN hypervisor (SDC scenario). Based on feedback from community we can increase number of VMs.

## Configure Docker

To configure Docker for device-mapper and Kata,

1. Stop Docker daemon if it is already running.

```bash
$ sudo systemctl stop docker
```

2. Set `/etc/docker/daemon.json` with the following contents.

```
{
  "storage-driver": "devicemapper"
}
```

3. Restart docker.

```bash
$ sudo systemctl daemon-reload
$ sudo systemctl restart docker
```

4. Configure [Docker](../Developer-Guide.md#update-the-docker-systemd-unit-file) to use `kata-runtime`.

## Configure Kata Containers with ACRN

To configure Kata Containers with ACRN, copy the generated `configuration-acrn.toml` file when building the `kata-runtime` to either `/etc/kata-containers/configuration.toml` or `/usr/share/defaults/kata-containers/configuration.toml`.

The following command shows full paths to the `configuration.toml` files that the runtime loads. It will use the first path that exists. (Please make sure the kernel and image paths are set correctly in the `configuration.toml` file)

```bash
$ sudo kata-runtime --show-default-config-paths
```

>**Warning:** Please offline CPUs using [this](offline_cpu.sh) script, else VM launches will fail.

```bash
$ sudo ./offline_cpu.sh
```

Start an ACRN based Kata Container,

```bash
$ sudo docker run -ti --runtime=kata-runtime busybox sh
```

You will see ACRN(`acrn-dm`) is now running on your system, as well as a `kata-shim`. You should obtain an interactive shell prompt. Verify that all the Kata processes terminate once you exit the container.

```bash
$ ps -ef | grep -E "kata|acrn"
```

Validate ACRN hypervisor by using `kata-runtime kata-env`,

```sh
$ kata-runtime kata-env | awk -v RS= '/\[Hypervisor\]/'
[Hypervisor]
  MachineType = ""
  Version = "DM version is: 1.2-unstable-254577a6-dirty (daily tag:acrn-2019w27.4-140000p)
  Path = "/usr/bin/acrn-dm"
  BlockDeviceDriver = "virtio-blk"
  EntropySource = "/dev/urandom"
  Msize9p = 0
  MemorySlots = 10
  Debug = false
  UseVSock = false
  SharedFS = ""
```
