Greetings everyone
It is I, the mighty Destroyer of Worlds, here to shed some light on the redstone that runs Planet Minecraft (and maybe point out some cool things from the end while I am at it). I won't have all of the answers as the only person that knows all of our hosting setup is Cyprezz, and he is not available at the moment, but server work is something that I do in my day job when not ending forgotten worlds, so I will explain some of your questions as I can.
First, some words. Domain refers to our name, specifically planetminecraft.com, Host is the pile of redstone computers that run the website, CloudFlare is a service that I will explain a little more in a bit, and DDoS is when a site is attacked by flooding it with too many requests.
First up is CloudFlare. CloudFlare is an accelerator that works by being our name server. What that does is translate planetminecraft.com into our IP address, kind of like asking where Zaralith lives, and finding out where you could mail me a package. What CloudFlare does, is instead of telling you where Planet Minecraft lives, it tells you where one of their storage buildings is (think a room full of chests near you), since they have a large number of servers all over the world, and many customers of theirs have far fewer.
What happens when you get to their server, is that they check your request ("Show me the_soup's awesome skin!") and make sure it is not spam (like asking 500 times in a row all at once). If your request is good, the system then looks at what you are asking for and looks to see if they have a copy. They will ask planetminecraft.com for the pieces of the page that they don't have, and give you their copy of the ones that they do have.
An example of this is this forums page. On this page, there is the Planet Minecraft logo at the top, some fun dirt on the outside edges, some code about how the text should look, and other little pictures and bits. CloudFlare saves all of those little pictures and bits of code, and only needs to ask for the words on the page if those pictures have not changed. This means that instead of needing to have PMC bring a whole stack of blocks, they only need to bring a few since CloudFlare has some of them already. This all makes our servers work for more people, and allows people to access the site faster.
For the 522 CloudFlare error, that means that the server that you connect to near you could not connect to PMC before it timed out. This can be caused by our servers being crashed by the volume of traffic, a problem between PMC and the CloudFlare server that you are connecting through, or a number of other issues.
You may ask, "Why don't you get more bigger servers!, this is crazy that you are always down!?". While I do not know the specifics of our current hosting, I know that in the past, we had so much traffic that our old provider told us to go away because they did not have enough servers for us to use. Servers are not cheap, and finding a large enough provider to handle massive traffic is difficult because there are not many. You may wonder how much traffic we actually get though and how that could possibly be too much.
According to the ranking services that I looked at, we are between the top 3500 sites and top 1000 sites in the world, and there are millions of those (so many millions that we are starting to need to make new street addresses to put them on). We also have a massive 1.5+ million submissions, from tiny skins to massive projects, and nearly 1.5 million users as well, with millions of pageviews a month. All of these numbers mean that we have a huge amount of data and a large group of people trying to access it all the time. The number of people that are on this site is pretty close to having a constant DDoS attack on us because of how many people visit.
I have rambled some about this issue, but at this time, we are working on trying to keep the site up and running, while working on new and improved things to help you share your creations and discussions with each other. We are happy that you love the site, and sad that the number of hugs you give it sometimes cause it to die, but know that we are working on the issue.
~Zaralith
