deploy.sh

#! /usr/bin/env bash

set -e  # Exit immediately if a command exits with a non-zero status.
set -u  # Treat unset variables as an error when substituting

# The .nix directory is where we put all our Nix output symlinks. Create it if it doesn't already exist.
mkdir --parents .nix

# Pin Nix to the exact version of nixpkgs we're using.
nix build -f nixpkgs.nix --out-link .nix/nixpkgs
export NIX_PATH=nixpkgs=$PWD/.nix/nixpkgs

# Build NixOS for the server.
nix build -v '(import ./default.nix).webserver1' \
  --out-link .nix/webserver1

# Get the path of the NixOS build in /nix/store.
NIXOS=$(readlink .nix/webserver1)

# Upload the build to the server.
nix copy "$NIXOS" --to ssh://example.com --no-check-sigs

# Set the system profile to the new build.
ssh example.com \
  sudo nix-env --profile /nix/var/nix/profiles/system --set "$NIXOS"

# Activate the new profile
ssh example.com \
  sudo /nix/var/nix/profiles/system/bin/switch-to-configuration switch