Zero-downtime deploys without Kubernetes

#!/usr/bin/env bash
set -Eeuo pipefail

APP=/home/deploy/app
REL="$APP/releases/$(date -u +%Y%m%dT%H%M%S)"

git --git-dir="$APP/repo" fetch --prune origin main
mkdir -p "$REL"
git --git-dir="$APP/repo" archive origin/main | tar -x -C "$REL"

ln -sfn "$APP/shared/.env" "$REL/.env"
ln -sfn "$APP/shared/uploads" "$REL/uploads"

cd "$REL"
npm ci --omit=dev
npm run build

# Atomic: ln -sfn on the same filesystem is a rename(2).
ln -sfn "$REL" "$APP/current.new"
mv -Tf "$APP/current.new" "$APP/current"

sudo systemctl reload-or-restart app
"$APP/bin/healthcheck" || { echo "health check failed"; exit 1; }

ls -1dt "$APP"/releases/* | tail -n +6 | xargs -r rm -rf

#!/usr/bin/env bash
# Poll until the new process answers, or fail after 30s.
for i in $(seq 1 30); do
  if curl -fsS --max-time 2 http://127.0.0.1:3000/healthz >/dev/null; then
    echo "healthy after ${i}s"
    exit 0
  fi
  sleep 1
done
exit 1

#!/usr/bin/env bash
set -Eeuo pipefail
APP=/home/deploy/app

# Second-newest release, i.e. the one before the current pointer.
PREV=$(ls -1dt "$APP"/releases/* | sed -n 2p)
ln -sfn "$PREV" "$APP/current.new"
mv -Tf "$APP/current.new" "$APP/current"
sudo systemctl restart app
echo "rolled back to $PREV"