Use harmonia instead of attic for binary cache

ci/known_hosts

@@ -0,0 +1 @@
+object-ctr.ams1.int.nul.ie ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFdHbZErWLmTPO/aEWB1Fup/aGMf31Un5Wk66FJwTz/8

ci/push-to-cache.sh

@@ -0,0 +1,29 @@
+#!/bin/sh
+set -e
+
+REMOTE_STORE=/var/lib/harmonia
+SSH_HOST="harmonia@object-ctr.ams1.int.nul.ie"
+SSH_KEY=/tmp/harmonia.key
+STORE_URI="ssh-ng://$SSH_HOST?ssh-key=$SSH_KEY&remote-store=$REMOTE_STORE"
+
+remote_cmd() {
+  ssh -i "$SSH_KEY" "$SSH_HOST" env HOME=/run/harmonia NIX_REMOTE="$REMOTE_STORE" "$@"
+}
+
+umask_old=$(umask)
+umask 0066
+echo "$HARMONIA_SSH_KEY" | base64 -d > "$SSH_KEY"
+umask $umask_old
+
+mkdir -p ~/.ssh
+cp ci/known_hosts ~/.ssh/
+path="$1"
+
+echo "Pushing $path to cache..."
+nix copy --no-check-sigs --to "$STORE_URI" "$path"
+
+echo "Updating profile..."
+remote_cmd nix-env -p "$REMOTE_STORE"/nix/var/nix/profiles/nixfiles --set "$path"
+
+echo "Collecting garbage..."
+remote_cmd nix-collect-garbage --delete-older-than 30d