How do I make a copy of my Linode for local development?

There are a couple of ways to do this. Your suggestion of using Docker is probably the simplest as it abstracts away the complexities of the hardware.

VirtualBox Method

You can create a VM in VirtualBox to install a custom distribution and then use Rescue Mode in the Linode Manager and Finnix image on your local computer to upload/download a raw disk image to/from your Linode. The following guides will be helpful:

• https://www.linode.com/docs/tools-reference/custom-kernels-distros/
• https://www.linode.com/docs/platform/disk-images/copying-a-disk-image-over-ssh/

Regarding the transfer method used in the pervious article, I was
able to speed up the disk image transfer on a Mac by adding
gzip/gunzip to the pipeline (for example):

ssh root@192.0.2.43 "dd if=/dev/sda | gzip " | gunzip | dd of=~/linode_image.img

Container Method

You can use docker to setup a container that holds your whole setup. In this case you will use your Linode only to run the container. The following is a guide that will help you get started with docker

We have plenty of other guides that cover different containers and provide example use cases.