darwin nix-daemon distributed builds

configure.sh

#!/usr/bin/env bash

sudo mkdir -p /run/nix/current-load
sudo launchctl unload /Library/LaunchDaemons/org.nixos.nix-daemon.plist
sudo rm /Library/LaunchDaemons/org.nixos.nix-daemon.plist
sudo curl -fsSL -o /Library/LaunchDaemons/org.nixos.nix-daemon.plist https://gist.github.com/LnL7/ba2eac19e77cd6b4bb02c8de03bf5f4e/raw/69722c2b13c4eb022a1312cd6891838b413e1f96/org.nixos.nix-daemon.plist
sudo launchctl load /Library/LaunchDaemons/org.nixos.nix-daemon.plist

# Configure /etc/nix/machines
# Make sure root can ssh to the builder (known_hosts etc.)
# Configure known hosts.

machines

mac1 x86_64-darwin /etc/nix/build_rsa 4
mac2 x86_64-darwin /etc/nix/build_rsa 4

org.nixos.nix-daemon.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>EnvironmentVariables</key>
	<dict>
		<key>NIX_BUILD_HOOK</key>
		<string>/nix/var/nix/profiles/default/libexec/nix/build-remote.pl</string>
		<key>NIX_CURRENT_LOAD</key>
		<string>/run/nix/current-load</string>
		<key>NIX_REMOTE_SYSTEMS</key>
		<string>/etc/nix/machines</string>
		<key>NIX_SSL_CERT_FILE</key>
		<string>/nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt</string>
	</dict>
	<key>KeepAlive</key>
	<true/>
	<key>Label</key>
	<string>org.nixos.nix-daemon</string>
	<key>LowPriorityIO</key>
	<false/>
	<key>Nice</key>
	<integer>0</integer>
	<key>ProcessType</key>
	<string>Interactive</string>
	<key>Program</key>
	<string>/nix/var/nix/profiles/default/bin/nix-daemon</string>
	<key>SoftResourceLimits</key>
	<dict>
		<key>NumberOfFiles</key>
		<integer>4096</integer>
	</dict>
</dict>
</plist>

These are some issues I've run into when setting it up:

• NIX_CURRENT_LOAD has to exist.
• make sure nix-store available in PATH (on the builder), this might not be the case for non-interactive ssh sessions on darwin.
• the machine was not in the know_hosts yet, what's important to know is that when using the nix-daemon this has to be done for root
• the signing key was not setup properly, I think this is not required when using the nix-daemon

WARNING: don't use nix-build --check to verify if this is working correctly, it always builds locally.

nix-build -E 'with import <nixpkgs> { system = "x86_64-darwin"; }; hello.overrideAttrs (drv: { REBUILD = builtins.currentTime; })'

• Why not store current load under /nix/var/run? Keeps all Nix files under /nix…
• Same for machines, this could go under /nix/etc/machines

None of the nix-daemon environment variables should be necessary anymore with nix 2.0