issues transferring to new host

hessodreamy

First of all, apologies if this is slightly out of the scope of the forum. The website is in php but this issue isnt really related directly to php.I couldn't find a suitable forum but suggestions are welcome.

I do the website for a small e-commerce company. People order and pay for goods on the site. I'm due to transfer my company website to a new server host. The new hosts have sensibly suggested taking the site down while the dns updates, but naturally we're not too keen if this can be avoided.

We've considered the mechanics of the site and THINK we can carry on running the site as normal. This is because the crucial stages of the process pass data between pages via POST variables. So we're thinking that even if the dns for a particular user's ISP updates to our new server during an order, the data will be passed along with the browser request, so it doesnt matter that the request arrives at a different server to the previous request.

Any more informed opinions would be welcomed!

Here's how the site works:
1. The user browses the site and chooses to put things in their shopping cart. This info is stored in a shopping cart array in the session.
2. This continues until the user comes to the checkout and puts in their personal info. Hereafter data is passed via POST variables.
3. Upon confirming the details of the order, the page directs to an external payment processing site. (this is done via POST)
4. Having processed the payment the customer is directed back to our site. (again, this is done via POST)
5. Upon arriving back at our site with data on whether the payment is OK, the order is written to the database.

So we are thinking that if the dns updates during browsing our site, the shopping cart array would drop out of the session, but that's no big deal.
If the dns updates while passing personal information to the external payment processors, the data would still be in the POST when it arrives at the next page on the new server, and we can then write it into the database.

Are there any holes in this reasoning? Naturally we'd have to keep track of the orders on each server, so we'd start with empty order tables, and then amalgamate them at the end of the exercise.

Thanks for reading this far,

Cheers
Shaun

bpat1434

The only problem I see is that from my understanding (not the fore-most authority obviously) is that Sessions are stored Server-side, and Cookies are user side. So let's say a user has a shopping cart full of items and goes to add one more. The DNS updates as they are adding the item. The session that they previously had is now destroyed because the new server doesn't recognize the session key. So their cart then defaults to the new item that they have (if you have the script(s) set up that way).

I would say just give people a warning. Their shopping may be interrupted between X and Y and if they can, try and not shop on between X and Y as to ensure that their orders are placed and handled properly. It has been my experience that any DNS change that I've done has been within 1 hour. Although most registrars tell you to wait for 24 - 36 hours for it to properly propogate through all the DNS servers.

Like I said, I'm not an authority on it, but I'm pretty sure that Sessions won't work, and using an intermittent "down-time" page would be helpful.

PHP Sessions (Manual)
[indent]An associative array containing session variables available to the current script.[/indent]

~Brett

hessodreamy

I am prepared that purchased items will fall out of existence during a dns update. I'd put up a warning that this may happen.

All i'm really concerned about is that the order details on the final page matches those received by the payment people (passed via post) and that their confirmation (also passed to us via post) matches that received by us.

If we can get away with it, and we can be sure that payments will be processed correctly, and will be recorded correctly in the database and displayed correctly to the customer (I know these are things i've not gone into) then we'd like to be able to leave it up and try to keep making money!

Any more input?