What is Cloud? -- Simple terms please

Cloud has been making a lot of noise and almost every tech (or tech related) person knows about it or at least heard of it. Now for those who have just heard about it but do not know what it means here is a quick definition from Dave Neilsen, the founder of Cloud-Camp. He says, "For something to be called cloud, it should have these properties :

• Hosted by someone else
• On-demand. Do not have to wait or call somebody to get it.
  
• Metered somehow. So you know exactly how much you are using and how much you are paying.
  
• Scalable, both ways - up and down as and when you require."
  

He goes on to say that Cloud could mean different things for different people. Here area few examples stating what cloud is for a particular person :

For an IT guy -- Infrastructure as Service
For a Web Developer -- Platform. Just dump your code and don't worry what runs it.
For a Business guy -- SaaS (Software as a Service)

That was pretty neat. Helps me answer the standard question "What the hell is this cloud thing?" in a sane manner. Earlier I could never figure out what a proper answer should be for this question, because there was so much to tell.

Here is my attempt to elaborate on above mentioned examples.

So cloud is basically having the infrastructure to do what you do hosted by someone else and having it totally scalable. For example, in the above list, for a web developer cloud is a platform where he can dump his code and expect it to run as he has designed it. He does not worry about the machines, the network connectivity, the bandwidth. He just pays for those in a metered manner. He scales his platform whenever he wants. He can increase his bandwidth quota, move to a better machine, increase the number of machines and all of this without calling the customer care or the sales guy. He will do it by logging into the cloud services website or he would have a script do this for him automatically, i.e if he is geek enough.

Similarly for a business man, it is software as a service. E-mail service would probably be a good example. The business man does not know what software runs the email system, he does not worry about what version of email server is running, what os it is running on, what DB it is using to store the emails, what protocols it is making use of. If the email contents are not that sensitive he would not even worry about the physical location of the servers storing these emails. He just buys the email software as a service and uses it. All that he probably worries about is how many email accounts are available to him/his company and how reliable/usable they are. At any point he can increase or decrease the number of accounts, once again without making a call.

That's cloud .

Note : I got this definition from one of the IBM developerWorks podcasts which is available here.

Oh, and remember, all this time every reference to Cloud meant "Cloud Computing", not just plain "cloud"

Very high startup time for vim under screen (GNU-Screen) -- SESSION_MANAGER

I have been using GNU-Screen for a while now and it has been very useful. Today morning when I started working, I noticed that vim is taking unusually long time to start up. It was very irritating. I had faced this same issue some time back but I could not recall the solution. I just remembered that it had something to do with GNOME and the display settings. On searching I found a couple of posts which said that this is because of vim trying to connect to an X which either is on a distant machine (distant in terms of network delay) or it is trying to connect to an non-existent X server. Another post on Ubuntu forums suggested that this could be because of multiple entries for 127.0.0.1 in the /etc/hosts file. Various combination of commenting/un-commenting entries did not help. I checked the DISPLAY env variable. It looked good too.

Finally I resorted to the last option of using strace. strace did reveal interesting stuff. I saw the that the wait/delay was because of a connect() call. Here are a few lines from strace output :

:~$ cat strace.vim.out | grep connect
connect(3, {sa_family=AF_FILE, path="/tmp/.ICE-unix/6386"}, 21) = -1 ENOENT (No such file or directory)
connect(3, {sa_family=AF_FILE, path="/tmp/.ICE-unix/6386"}, 21) = -1 ENOENT (No such file or directory)
connect(3, {sa_family=AF_FILE, path="/tmp/.ICE-unix/6386"}, 21) = -1 ENOENT (No such file or directory)
connect(3, {sa_family=AF_FILE, path="/tmp/.ICE-unix/6386"}, 21) = -1 ENOENT (No such file or directory)
connect(3, {sa_family=AF_FILE, path="/tmp/.ICE-unix/6386"}, 21) = -1 ENOENT (No such file or directory)
connect(3, {sa_family=AF_FILE, path="/tmp/.ICE-unix/6386"}, 21) = -1 ENOENT (No such file or directory)
connect(3, {sa_family=AF_FILE, path="/tmp/.X11-unix/X0"}, 110) = 0
connect(3, {sa_family=AF_FILE, path="/tmp/.X11-unix/X0"}, 110) = 0
connect(3, {sa_family=AF_FILE, path="/tmp/.X11-unix/X0"}, 110) = 0
connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
connect(4, {sa_family=AF_FILE, path="/var/centrifydc/daemon2"}, 25) = 0

This confirmed the fact that it was a network related thing, i.e vim is trying to connect to something that did not exist. I thought my X (or GDM to be more precise) was screwed up and thought of logging out and logging back in. I thought of doing some more experiments with this setup to find out what caused the problem.

All of this was running under my gnu-screen session. I opened another gnome terminal to read the redirected output of strace. Accidentally I used vim itself to open the file. Before I realized my mistake and I could start cursing myself, vim popped up..! It was there up and running as fast as it could be... !! Then it hit me that it could be my screen session which is causing this. I did not know how to find the differences in the two environments - in and out of screen. To solve this particular problem I ran strace on vim in the new terminal so that I could compare the two and find out what is lacking. Here is what strace told me in the terminal outside screen :

:~$ cat outside.strace.vim.out | grep connect
connect(3, {sa_family=AF_FILE, path="/tmp/.ICE-unix/28919"}, 22) = 0
connect(4, {sa_family=AF_FILE, path="/tmp/.X11-unix/X0"}, 110) = 0
connect(5, {sa_family=AF_FILE, path="/tmp/.X11-unix/X0"}, 110) = 0
connect(6, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
connect(6, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
connect(6, {sa_family=AF_FILE, path="/var/centrifydc/daemon2"}, 25) = 0

The difference in the path was obvious. On searching through the list of environment variables SESSION_MANAGER came up. It is the variable which will tell all gnome based apps how to contact the X (or the GNOME session). I do not know what caused this disparity, but most likely setting the appropriate value inside the screen session would have worked. Well it would have worked in one of the screen windows in which I change the value. I have several such windows, so I just chose to start a new screen session.