Network setup without involvement from guest?

[danthegoodman1]

As found in https://github.com/firecracker-microvm/firecracker/blob/main/docs/network-setup.md in order for the guest to have internet access, they still need to run commands like:

ip addr add 172.16.0.2/24 dev eth0
ip link set eth0 up
ip route add default via 172.16.0.1 dev eth0

This is only useful if they have the ip command on the system. For something like the default minimal ubuntu docker image

mkdir rootfs
docker export $(docker create ubuntu) | tar -C rootfs -xf -

ip is not installed by default.

For a guest that does not have the capability (or intention) to setup their own network routes, is there a way that this can be done from the host (or through some modification of the rootfs?)

My goal is to be able to give any container image internet access when run with firecracker.

I used the following script to make my ext4 rootfs, and replaced it with the ubuntu one in the getting started guide script:

#!/bin/bash

# Variables
ROOTFS_DIR="./rootfs"
IMAGE_FILE="rootfs.ext4"
IMAGE_SIZE_MB=100  # Adjust size as needed
TEMP_MOUNT_DIR="/mnt/tempfs"

cp resolv.conf $ROOTFS_DIR/etc/resolv.conf
mkdir -p $ROOTFS_DIR/etc/network
cp interfaces $ROOTFS_DIR/etc/network/interfaces

# Step 1: Create an empty file
dd if=/dev/zero of=${IMAGE_FILE} bs=1M count=${IMAGE_SIZE_MB}

# Step 2: Format the file as ext4
mkfs.ext4 ${IMAGE_FILE}

# Step 3: Mount the ext4 file
mkdir -p ${TEMP_MOUNT_DIR}
sudo mount -o loop ${IMAGE_FILE} ${TEMP_MOUNT_DIR}

# Step 4: Copy the root filesystem
sudo cp -a ${ROOTFS_DIR}/. ${TEMP_MOUNT_DIR}

# Step 5: Unmount the ext4 file
sudo umount ${TEMP_MOUNT_DIR}

# Step 6: Clean up
rmdir ${TEMP_MOUNT_DIR}

echo "ext4 filesystem image created: ${IMAGE_FILE}"

[danthegoodman1]

Adding this to the boot arg seems to work for me! I found this following this guide and specifically this line. I looked up the kernel docs for the ip param and edited my config as needed

FC_IP="172.16.0.2"
MASK_LONG="255.255.255.0"
KERNEL_BOOT_ARGS="${KERNEL_BOOT_ARGS} ip=${FC_IP}::${TAP_IP}:${MASK_LONG}::eth0:off"

See full: https://gist.github.com/danthegoodman1/476cb5a8671fb94d1727ea893c5b485c