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How to Create a custom OS image on Azure for starting Debian buster VMs

Debian 10, nicknamed as buster has reached its end of life. If you need to start a new VM using this OS to run your legacy app, these instructions might help.

Requisite tools

1. az cli (https://learn.microsoft.com/en-us/cli/azure/install-azure-cli-linux?pivots=apt)
2. azcopy cli (https://learn.microsoft.com/en-us/azure/storage/common/storage-use-azcopy-v10#download-azcopy)
3. wget, tar, qemu-img, stat

Process

1. Download the disk image from debian archives

   wget https://cloud.debian.org/images/cloud/buster/latest/debian-10-azure-amd64.tar.xz
   

2. Extract the archive to get disk.raw file

   tar -xf debian-10-azure-amd64.tar.xz
   

3. Convert the disk to VHD format that is compatible with Azure disks

   1. Get a multiple of 1 MB that is large enough to hold raw disk

      MB=$((1024 * 1024))
      RAW_SIZE=$(stat -c%s "disk.raw")
      ROUNDED_SIZE=$((($RAW_SIZE/$MB + 1)*$MB))
      

   2. Ensure the size of the disk.raw is a multiple of 1 MB (required by Azure)

      qemu-img resize -f raw disk.raw $ROUNDED_SIZE
      

   3. Convert disk.raw to fixed-size debian-buster.vhd

      qemu-img convert -f raw -o subformat=fixed,force_size -O vpc disk.raw debian-buster.vhd
      

4. Choose a resource group and location where you want to work in Azure

   export CHOSEN_GROUP=chosen-group-name
   export CHOSEN_LOCATION=chosen-location-eg-centralus
   

5. Upload the VHD contents to an Azure disk
   1. Create disk container

      az disk create \
         --resource-group $CHOSEN_GROUP \
         --name debian-buster-os-disk \
         --location $CHOSEN_LOCATION \
         --upload-type Upload \
         --upload-size-bytes $ROUNDED_SIZE \
         --sku Standard_LRS
      

   2. Get SAS write url for the disk container

      SAS_URL=$( \
         az disk grant-access \
            --resource-group $CHOSEN_GROUP \
            --name debian-buster-os-disk \
            --access-level Write \
            --duration-in-seconds 3600)
      

   3. Upload debian-buster.vhd content to the disk container

      azcopy copy --blob-type PageBlob "debian-buster.vhd" "${SAS_URL}"
      

   4. Close/conclude writing to the disk

      az disk revoke-access --resource-group $CHOSEN_GROUP --name debian-buster-os-disk
      

6. Create an OS image from the uploaded OS disk

   az image create \
      --resource-group $CHOSEN_GROUP \
      --location $CHOSEN_LOCATION \
      --name DebianBusterCustomOSImage \
      --source debian-buster-os-disk \
      --os-type Linux
   

7. Once image is generated and visible in Azure portal, the debian-buster-os-disk is no more needed. Delete it to save storage bills;

   az disk delete --resource-group $CHOSEN_GROUP --name debian-buster-os-disk
   

8. Check if the newly created image with name DebianBusterCustomOSImage visible in the azure portal? If yes, use it with the portal to launch VMs just like any other OS for the vm.

Making apt update to work on the Debian buster VM

Once VM is started and you are able to login to it, if you try apt update command, it fails. This is because it trying to pull packages lists from locations that are no more there. To fix this, edit /etc/apt/sources.list file and make sure that all source urls are pointing towards archive.debian.org. Once done, save the file and enjoy apt updates as normal.