Sent from my iPhone On Oct 27, 2011, at 11:26, Bryan Taylor <btay...@rackspace.com> wrote:
> On 10/27/2011 10:36 AM, George Reese wrote: > >> #3 Push scales a hell of a lot better than having tools polling a cloud >> constantly. It doesn't matter whether it is polling the API, polling a >> feed, or polling a message queue. Polling is one of the most unscalable >> things you can do in any distributed systems scenario. Calling it a feed >> doesn't magically solve the problem. Actually, it's quite hard on its >> own in an IaaS scenario and has scaling issues independent of the >> polling issue. > > I disagree. The web was designed specifically to solve the distributed > scaling problem and it's based on HTTP polling. It scales pretty well. The > argument against polling not scaling inevitably neglects using caching > properly. > The web was not designed to deal with a bunch of clients needing to know about infrastructure changes the instant they happen. And API data should not be cached. The Rackspace API used to do that, and it created a mess. > Push doesn't scaled because it requires the server to know about every client > and track conversational state with them. No, it doesn't. You push changes as they occur to a message queue. A separate system tracks subscribers and sends them out. There is no conversational state if done right. > If you need reliability, this requires persisting that conversational state. > In order to allow this to happen you have to have some kind of registration > protocol for clients. If some fraction of those clients are flaky, the > conversational state tracking will kill you because each client consumes > resources and so flaky clients = resource leak. > > Push wins when you need very low latency delivery, high message throughput to > individual consumers, or server side guarantees of delivery to individual > consumers, but not for scaling to a large number of clients in a climate of > an elastic infrastructure. > >> Push notifications are the only mechanism for solving the scaling issue. >> You push any changes to a message queue. Agents pick up the changes and >> send them on to subscriber endpoints. Not that hard. > > Not that hard with a few fairly reliable clients. Very hard with a web scale > set of unreliable clients while I simultaneously need to scale the back end. _______________________________________________ Mailing list: https://launchpad.net/~openstack Post to : openstack@lists.launchpad.net Unsubscribe : https://launchpad.net/~openstack More help : https://help.launchpad.net/ListHelp
