Creating an OpenWrt image for Scaleway Instances

This tutorial shows how to build a custom image for Scaleway from scratch using the new export/import feature.

It introduces the basic needs and actions to create a custom image, but each operating system may have specifics that need to be troubleshooted individually.

To create a custom image, you need to build a QCOW2 image and create a snapshot from it.

The following steps are required to create the image:

• Download an OS disk image
• Convert it to QCOW2 (if not provided in this format)
• Edit the image to fit Scaleway's ecosystem
• Upload the image to Scaleway Object Storage
• Convert to Snapshot through import
• Test the image and troubleshoot via the Console

Before you start

To complete the actions presented below, you must have:

• A Scaleway account logged into the console
• Owner status or IAM permissions allowing you to perform actions in the intended Organization
• An SSH key
• An Object Storage bucket

The following commands are done on an Ubuntu 22.04.

Download the image

The needed image must be a full disk image, not an ISO image or only a rootfs.

In order to work on Scaleway Instances, the image must be using EFI (not just BIOS) to boot.

OpenWrt images are available here, we are going to use a stable release, for x86_64 architecture, with EFI.

Download the image we are going to use in this tutorial:

curl -sSLO https://downloads.openwrt.org/releases/24.10.1/targets/x86/64/openwrt-24.10.1-x86-64-generic-ext4-combined-efi.img.gz
gunzip openwrt-24.10.1-x86-64-generic-ext4-combined-efi.img.gz

Prepare the QCOW2 image

1. Install the needed QEMU tools:

   apt-get install qemu-utils -y

2. Convert the image and resize the target disk size (minimum disk size at Scaleway = 1 GB):

   qemu-img convert -f raw -O qcow2 openwrt-24.10.1-x86-64-generic-ext4-combined-efi.img openwrt-24.10.1-x86-64-generic-ext4-combined-efi.qcow2
   qemu-img resize openwrt-24.10.1-x86-64-generic-ext4-combined-efi.qcow2 1G

3. Mount the QCOW2 image as a device

   modprobe nbd
   qemu-nbd -c /dev/nbd0 openwrt-24.10.1-x86-64-generic-ext4-combined-efi.qcow2

   Important

   Conversion and resizing create errors in the partition table which are fixed when re-writing it using fdisk. Furthermore, To resize the main partition, the partition number must be found.

   To print and fix the partition table, do:

   echo 'p\nw\n' | fdisk /dev/nbd0

4. Resize the main partition to fit the available space (partition number 2 in the example above):

   growpart /dev/nbd0 2
   resize2fs /dev/nbd0p2

Edit the image content

1. Mount the image:

   mkdir -p /mount/temp
   mount /dev/nbd0p2 /mount/temp

   OpenWrt needs two interfaces to work (WAN and LAN). But a default Instance only provides one interface. We are going to use the dummy module to add an interface.

2. Download the package.

   curl -sSL -o /mount/temp/kmod-dummy_5.10.146-1_x86_64.ipk https://downloads.openwrt.org/releases/24.10.1/targets/x86/64/packages/kmod-dummy_5.10.146-1_x86_64.ipk

3. Chroot in the image.

   chroot /mount/temp/ /bin/ash

4. Install the package.

   mkdir -p /tmp/lock
   opkg install kmod-dummy_5.10.146-1_x86_64.ipk
   rm -rf /tmp/* kmod-dummy_5.10.146-1_x86_64.ipk

5. Set the root password, whilst in the chroot. In OpenWrt, it is used by the web interface for login.

   passwd

6. Configure the web server ports and redirect http to https using the uci CLI of OpenWrt.

   uci del uhttpd.main.listen_http
   uci add_list uhttpd.main.listen_http='0.0.0.0:8080'
   uci del uhttpd.main.listen_https
   uci add_list uhttpd.main.listen_https='0.0.0.0:8443'
   uci set uhttpd.main.redirect_https=1
   uci commit uhttpd

7. Disable password authentication in SSH.

   uci set dropbear.@dropbear[0].PasswordAuth=off
   uci set dropbear.@dropbear[0].RootPasswordAuth=off
   uci commit dropbear

Configure SSH access

Since we have disabled password authentication in SSH, we need a way to load SSH keys when running.

In this tutorial, we do not set up cloud-init, but use the same magic IP mechanism to get the keys.

1. Create the authorized_keys file:

   touch /etc/dropbear/authorized_keys
   chmod 600 /etc/dropbear/authorized_keys

2. Create the fetch script:

   cat <<EOF>/etc/init.d/fetch_ssh_keys
   #!/bin/sh /etc/rc.common
   
   START=97
   
   start() {
       echo -e "\nFetching SSH keys from Scaleway Metadata" > /dev/console
       wget -qO- http://169.254.42.42/conf | egrep 'SSH_PUBLIC_KEYS_._KEY' | cut -d'=' -f2- | sed "s/'//g" > /etc/dropbear/authorized_keys
   }
   
   reload() {
       start
   }
   EOF
   chmod +x /etc/init.d/fetch_ssh_keys

3. Add the script to rc.d.

   ln -s /etc/init.d/fetch_ssh_keys /etc/rc.d/S97fetch_ssh_keys

4. Exit the chroot.

   exit

Configure the network

1. Configure the network to be able to use the image on a Scaleway Instance:

   cat <<EOF>/mount/temp/etc/config/network
   config interface 'loopback'
   option device 'lo'
   option proto 'static'
   option ipaddr '127.0.0.1'
   option netmask '255.0.0.0'
   
   config interface 'wan'
   option device 'eth0'
   option proto 'dhcp'
   
   config interface 'lan'
   option device 'dummy0'
   option proto 'static'
   option ipaddr '192.168.0.1'
   option netmask '255.255.255.0'
   EOF

   Important

   eth0 is the first interface associated by Scaleway Instances to the public network (WAN) and needs to be available to our DHCP server for configuration.

2. Add firewall rules to redirect WAN ports to LAN ports. This is required, as accessing the UI and SSH in OpenWrt is normally only possible through the LAN interface.

   cat <<EOF>>/mount/temp/etc/config/firewall
   # port redirect UI ACCESS and SSH
   config redirect
   option name             HTTP-UI
   option src              wan
   option src_dport        8080
   option desti            lan
   option dest_ip          192.168.0.1
   option dest_port        8080
   option proto            tcp
   
   config redirect
   option name             HTTPS-UI
   option src              wan
   option src_dport        8443
   option dest             lan
   option dest_ip          192.168.0.1
   option dest_port        8443
   option proto            tcp
   
   config redirect
   option name             SSH
   option src              wan
   option src_dport        22
   option dest             lan
   option dest_ip          192.168.0.1
   option dest_port        22
   option proto            tcp
   EOF

3. Unmount the image container to finish editing its content.

   umount /mount/temp
   qemu-nbd -d /dev/nbd0

Import the image

You can use the Scaleway console or your favorite Amazon S3-compatible CLI tool to upload objects into a bucket.

In this example, we use the AWS CLI.

1. Import the image into your bucket:

   aws s3 cp openwrt-24.10.1-x86-64-generic-ext4-combined-efi.qcow2 s3://my-import-bucket/openwrt.qcow2

2. Trigger the import of the image as a snapshot in one of the regions where the bucket is located, using SCW CLI:

   scw block snapshot create name=openwrt volume-type=b_ssd bucket=my-import-bucket key=openwrt.qcow2

3. Create the corresponding Instance image:

   scw instance image create name=openwrt arch=x86_64 snapshot-id=$(scw instance snapshot list | grep -m1 openwrt | awk '{print $1}')

Testing and troubleshooting the image

1. Create an Instance using the snapshot image:

   scw instance server create type=DEV1-S name=scw-openwrt ip=new image=$(scw instance image list | grep -m1 openwrt | awk '{print $1}')

2. Troubleshoot the boot behavior and configuration using the console of your Instance:

   scw instance server console $(scw instance server list | grep -m1 scw-openwrt | awk '{print $1}')

3. Exit the console using Ctrl+q.

You can access the web console of OpenWrt using https://<public ip of instance>:8443