I have a gut feeling this isn't going to work that well. The reasons include: - Backwards compatibility: how is a large site going to upgrade from 1.9 to 1.10? - Complexity of setup. - Error conditions: for example, what happens when an interface server sends a request to worker, and then dies (that is, the response channel has zero listeners). Similarly for chunked messages. - Does the architecture really scale enough? The channel backend is going to be a bottleneck, it needs the ability to handle a huge amount of data and a huge amount of individual messages. In particular, the request channel is going to be contested. We know classic http scales, but is the same true for interface server architecture? - Performance. Each request and response needs two additional network roundtrips. One to save to the channel server, one to fetch from the channel server. If the messages are large, this adds a lot of latency. - Untested architecture: does any big site use this kind of architecture for all http handling?
A realistic test for this is to push a scalable amount of scalable sized requests through the stack. The stack should recover even if you shut down parts of the network, any single interface server, channel backend server or worker server. Of course, when a server or a part of the network recovers, the stack would need to recover from that. Compare the performance, simplicity of setup and ability to recover from error conditions to a setup with only classic Django http servers. I'm sorry if this feels negative. But, you are planning to change the very core of what a Django server is, and I feel we need to know with certainty that the new architecture really works. And not only that, it needs to be at least as good as classic http handling for existing users. - Anssi On Thursday, December 17, 2015, Andrew Godwin <and...@aeracode.org> wrote: > Yes, that is the idea. While it obviously adds overhead (a millisecond or > two in my first tests), it also adds natural load balancing between workers > and then lets us have the same architecture for websockets and normal HTTP. > > (The interface server does do all the HTTP parsing, so what gets sent over > is slightly less verbose than normal HTTP and needs less work to use, but > it's not a big saving) > > Andrew > > On Thu, Dec 17, 2015 at 9:01 PM, Anssi Kääriäinen <akaar...@gmail.com > <javascript:_e(%7B%7D,'cvml','akaar...@gmail.com');>> wrote: > >> Is the idea a large site using classic request-response architecture >> would get the requests at interface servers, these would then push the HTTP >> requests through channels to worker processes, which process the message >> and push the response through the channel backend back to the interface >> server and from there back to the client? >> >> - Anssi >> >> On Thursday, December 17, 2015, Andrew Godwin <and...@aeracode.org >> <javascript:_e(%7B%7D,'cvml','and...@aeracode.org');>> wrote: >> >>> To address the points so far: >>> >>> - I'm not yet sure whether "traditional" WSGI mode would actually run >>> through the in memory backend or just be plugged in directly to the >>> existing code path; it really depends on how much code would need to be >>> moved around in either case. I'm pretty keen on keeping a raw-WSGI path >>> around for performance/compatability reasons, and so we can hard fail if >>> you try *any* channels use (right now the failure mode for trying to use >>> channels with the wsgi emulation is silent failure) >>> >>> - Streaming HTTP responses are already in the channels spec as chunked >>> messages; you just keep sending response-style messages with a flag saying >>> "there's more". >>> >>> - File uploads are more difficult, due to the nature of the worker model >>> (you can't guarantee all the messages will go to the same worker). My >>> current plan here is to revise the message spec to allow infinite size >>> messages and make the channel backend handle chunking in the best way >>> (write to shared disk, use lots of keys, etc), but if there are other >>> suggestions I'm open. This would also let people return large http >>> responses without having to worry about size limits. >>> >>> - Alternative serialisation formats will be looked into; it's up to the >>> channel backend what to use, I just chose JSON as our previous research >>> into this at work showed that it was actually the fastest overall due to >>> the fact it has a pure C implementation, but that's a year or two old. >>> Whatever is chosen needs large support and forwards compatability, however. >>> The message format is deliberately specified as JSON-capable structures >>> (dicts, lists, strings) as it's assumed any serialisation format can handle >>> this, and so it can be portable across backends. >>> >>> - I thought SCRIPT_NAME was basically unused by anyone these days, but >>> hey, happy to be proved wrong. Do we have any usage numbers on it to know >>> if we'd need it for a new standalone server to implement? It's really not >>> hard to add it into the request format, just thought it was one of those >>> CGI remnants we might finally be able to kill. >>> >>> Andrew >>> >>> On Thu, Dec 17, 2015 at 6:32 PM, Anssi Kääriäinen <akaar...@gmail.com> >>> wrote: >>> >>>> On Thursday, December 17, 2015, Carl Meyer <c...@oddbird.net> wrote: >>>> >>>>> Hi Andrew, >>>> >>>> >>>>> - I share Mark's concern about the performance (latency, specifically) >>>>> implications for projects that want to keep deploying old-style, given >>>>> all the new serialization that would now be in the request path. I >>>>> think >>>>> some further discussion of this, with real benchmark numbers to refer >>>>> to, is a prerequisite to considering Channels as a candidate for Django >>>>> 1.10. To take a parallel from Python, Guido has always said that he >>>>> won't consider removing the GIL unless it can be done without >>>>> penalizing >>>>> single-threaded code. If you think a different approach makes sense >>>>> here >>>>> (that is, that it's OK to penalize the simple cases in order to >>>>> facilitate the less-simple ones), can you explain your reasons for that >>>>> position? >>>>> >>>> >>>> We would also need some form of streamed messages for streamed http >>>> responses. >>>> >>>> Is it possible to handle old-style http the way it has always been >>>> handled? >>>> >>>> - Anssi >>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "Django developers (Contributions to Django itself)" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to django-developers+unsubscr...@googlegroups.com. >>>> To post to this group, send email to django-developers@googlegroups.com >>>> . >>>> Visit this group at https://groups.google.com/group/django-developers. >>>> To view this discussion on the web visit >>>> https://groups.google.com/d/msgid/django-developers/CALMtK1Gz%3DaYMLyFW2da2C6Wo_-c_V2T_4p6K9eh0vwrKB91dKw%40mail.gmail.com >>>> <https://groups.google.com/d/msgid/django-developers/CALMtK1Gz%3DaYMLyFW2da2C6Wo_-c_V2T_4p6K9eh0vwrKB91dKw%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Django developers (Contributions to Django itself)" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to django-developers+unsubscr...@googlegroups.com. >>> To post to this group, send email to django-developers@googlegroups.com. >>> Visit this group at https://groups.google.com/group/django-developers. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/django-developers/CAFwN1upm8N8tOhCdAgPEbYbBO6MU%2BmnEQ%3D%3Dp6EmW75%3DbNXHkfg%40mail.gmail.com >>> <https://groups.google.com/d/msgid/django-developers/CAFwN1upm8N8tOhCdAgPEbYbBO6MU%2BmnEQ%3D%3Dp6EmW75%3DbNXHkfg%40mail.gmail.com?utm_medium=email&utm_source=footer> >>> . >>> For more options, visit https://groups.google.com/d/optout. >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "Django developers (Contributions to Django itself)" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to django-developers+unsubscr...@googlegroups.com >> <javascript:_e(%7B%7D,'cvml','django-developers%2bunsubscr...@googlegroups.com');> >> . >> To post to this group, send email to django-developers@googlegroups.com >> <javascript:_e(%7B%7D,'cvml','django-developers@googlegroups.com');>. >> Visit this group at https://groups.google.com/group/django-developers. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/django-developers/CALMtK1FOVa6K-MMsZ9vACfcw0w0KHwdCXJ2vxu7_Y5Q9PHJ6Gg%40mail.gmail.com >> <https://groups.google.com/d/msgid/django-developers/CALMtK1FOVa6K-MMsZ9vACfcw0w0KHwdCXJ2vxu7_Y5Q9PHJ6Gg%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> >> For more options, visit https://groups.google.com/d/optout. >> > > -- > You received this message because you are subscribed to the Google Groups > "Django developers (Contributions to Django itself)" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to django-developers+unsubscr...@googlegroups.com > <javascript:_e(%7B%7D,'cvml','django-developers%2bunsubscr...@googlegroups.com');> > . > To post to this group, send email to django-developers@googlegroups.com > <javascript:_e(%7B%7D,'cvml','django-developers@googlegroups.com');>. > Visit this group at https://groups.google.com/group/django-developers. > To view this discussion on the web visit > https://groups.google.com/d/msgid/django-developers/CAFwN1uoCX67D4E5J8n_wOo3VvPVjZYVnOG%2BshX6oDQk3zgu3vw%40mail.gmail.com > <https://groups.google.com/d/msgid/django-developers/CAFwN1uoCX67D4E5J8n_wOo3VvPVjZYVnOG%2BshX6oDQk3zgu3vw%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group. 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