Websites go down; it’s a fact of life. But you can minimize your downtime with a few simple tools.
I use Uptime Robot to get notifications when my site goes down.
You can see the status of all my sites here:
Other options (which I haven’t tried myself):
All my sites use CloudFlare, which acts as a CDN, manages DNS, improves security (especially in preventing DDoS attacks), and can also serve a cached, static version of your site in case the real thing goes down.