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© Võ Minh Thu, 2019.

Toplevel: updating a running virtual machine

nix-build -A toplevel
@result@

In the blog post Industrial-strength Deployments in Three Commands, the toplevel is defined as

let
  nixos = import <nixpkgs/nixos> {
    configuration = import ./configuration.nix;
  };
in
  nixos.system

and is described as being the whole system. To be specific, the closure of toplevel is a complete system and can be packaged as a rootfs, or in our case as a qcow2 virtual machine image. It also contains a script to "activate" the system, for instance by copying files into /etc/.

To update a remote NixOS machine, the toplevel closure can be uploaded to it, then activated there. See the above blog post for a description.

Say for instance that we update site/index.html, then we can update an existing droplet with:

$ ./deploy.sh

instead of re-building a complete virtual machine image and provisioning a new droplet.

TODO The droplet IP address is currently hard-coded in the deploy.sh script.

TODO Elaborate if I should copy the target /etc/nixos/ configuration. I think I check and that it only imports the user-data and the file from nixpkgs that I already have.

TODO Check the links provided in the blog post for additional insights.