(rahaeli) For those of you who don't speak geek, I'll do a translation and explanation of some of the geek terms that are probably going to be thrown around over the next few hours!
(For those of you who do speak geek: yeah, I know, I'm oversimplifying in a lot of cases.)
BigIP: The BigIP is a piece of hardware that sits at the very front of our network, and acts as the doorman. When a request knocks on our door, the BigIP finds the webserver that's least busy and says "hey, go over there." Of course, it works a heck of a lot faster than any person could.
CAPTCHA: Stands for "Completely Automated Public Turing Test to Tell Computers and Humans Apart". (Yeah, I know, the acronym and the expansion don't quite match.) These are those little "prove you're a human" graphics you see when you create a new account or sometimes when you comment anonymously. There's a very slight chance that we might run out of pre-stored captchas during the move, which means that people might not be able to create accounts or comment anonymously, since the job that makes more of them won't be running.
cron / cron job: A cron job is like an automated set of instructions that'll run at a set time. We use cron jobs to schedule maintenance tasks. Most of them are invisible to you guys, but some examples are things like the emails that go out to warn people whose accounts are about to expire. We schedule those to run on a regular basis, so nobody has to manually sit there and send out all those emails. Part of the move is making sure that all the cron jobs are running on the right machines at the right time.
DNS: DNS stands for "Domain Name Service". It's what your computer uses to know that requests for "http://www.livejournal.com" should come to our computers, but "http://www.google.com" should go to Google, for instance. Part of what we're doing tonight is the Internet equivalent of filling out a "change of address" card with the post office -- telling all the "address books" on the Internet that we've moved.
IP address: Your IP address is what distinguishes your computer from every other community on the Internet. Every machine on the Internet has an IP address. DNS (see above) is what maps an IP address to a domain name. Because we're switching to a new provider, our IP address is changing, which means that we're going to have to broadcast a new IP address through DNS.
mailgate: This is the process that handles all the mail coming into LiveJournal and makes sure that it goes where it needs to go. It handles things like emailed Support requests, picture posts, mobile posts, etc.
memcache/memcached: Memcache is something that we came up with to store the most-frequently-used data in our servers' memory, instead of having to load it all from the database every time someone needs it. We do this because reading from memory is fast, and reading from the database's disks is slow. Of course, we're talking about fractions of a second, but when we're dealing with eight million of you, fractions of a second add up quickly!
mogile: In traditional LiveJournal fashion, we couldn't find a file arrangement system that we liked, so we wrote our own! MogileFS -- an anagram of "omg files" -- is what stores and retrieves all of our data files, like userpics and phone posts. Of course, it's a little more complicated than just your hard drive ...
nfs: NFS is a way of making sure that a bunch of different computers on a network can share a single bunch of files. It basically pretends that a hard drive on a different computer is really on your computer. That way, we can have all of the LJ files in one place, and all the other computers on the network can use that server, instead of having to copy files all over to our hundreds of different web servers.
perlbal: If the BigIP is the hardware doorman of the network, perlbal (short for "perl balancer" -- perl is the computer language it's written in) is the software doorman. It's a piece of software that takes all the connections in and makes sure that they go to the right place.
replication: When you've got two databases talking to each other, replication is the process of them sharing information back and forth. There are a bunch of different possible database configurations, but in all of them, data is passed back and forth pretty regularly. Part of tonight's move involves starting and stopping replication back and forth from various databases.
smtp: Stands for Simple Mail Transport Protocol. This is what handles all the mail going out -- comment notification emails, Support request responses, and mail to your @livejournal.com email.
ttl: Time To Live. To really explain this I'd have to draw pictures! It's a setting that you can use in your DNS server configuration, to tell your DNS server how long to cache the answer. Basically, when your computer asks "Hey, if I want to go to www.livejournal.com, what IP address does that correspond to?", the server says "Here's the address!" It doesn't do that every time, though, to make things faster -- it saves the answer for later. By setting a low TTL, we make it go back and look up the real answer more frequently, in case it changes. Part of tonight involves setting a low TTL. Kind of like your pesky little brother -- every five minutes, it's going to poke us and whine, "Hey, didja move yet? Didja move yet? Didja mooooooove yet?"
And there you have it! If our engineers wind up using any terms that I haven't covered, I'll hop in and try to define them.
