I have 2 python servers running independently of one another but sharing the same database. They need to communicate with each other about when certain changes have been made to the database so the other server (if running) can reload cached data.
What would be my best options for communicating between two such programs?
I've thought of using sockets but it seems like a lot of work. Either one program will be polling connect whenever the other is off, or they both need to have server/client capabilities. I looked into named pipes but didn't see any easy portable solution (needs to run on windows and unix).
You could have each one implement a simple XMLRPC server. Each one can then execute code in the other, such as telling the other one it needs to update.
The easiest way is to use the database itself as a means of communication. Add a table for logging updates. Then, either machine can periodically query to see if the underlying data has been changed.
Another easy form of communication is email using the smtplib module. Our buildbots and version control repository use this form of communication.
If you want something with a little more "industrial" strength, consider using RabbitMQ or somesuch for messaging between servers.
I agree that sockets are usually too low-level. If you investigate "RabbitMQ", you should also investigate celery. It can use RabbitMQ as a back-end, but it can also use the database, and it neatly encapsulates the messaging mechanism. It is also integrated with django and gevent.
Related
I am creating an application that basically has multiple connections to a third party Chat Streaming API(Socket based).
The way it works is - Every user has an account on my app and another account on the third party app. He gives me an access token for the third party chat app and I connect to the third party API to stream his chats. This happens for hundreds of users.
I need to create a socket connection pool for every user and run parallel threads. I am using a python library(for that API) and am able to achieve real time feeds for single users. How do I implement an asynchronous socket connection pool in Python or NodeJS? I have a Linux micro instance on EC2 and I need to run this application for 1000 users.
I am exploring Redis+Tornado to implement this. Are there any better alternatives?
This will be messy and also a couple of things to consider.
If you are going to use multiple threads remember that you can only run so many per CPU as the OS permits, rather go multiprocessing.
If you are going async with long polling processes it will prevent other clients from processing requests.
Solution
When your application absolutely needs to be real-time I would suggest websockets for server-client interaction.
Then from your clients request start a single process that listens\polls on your streaming API using multiprocessing in python. So you will essentially create a separate process for each client.
And now, to make your WebSocketHandler and Background API Streamer interact with each other you can use the Observer Pattern (https://en.wikipedia.org/wiki/Observer_pattern) to notify the WebSocket that you have received data from the API.
Make sure that you assign a unique ID to every client and make sure that you only post the data to the intended client when using websockets.
EDIT:
Web:
Also on your question regarding Tornado. It is a good lightweight framework for running a couple of users maybe 1000. But anything more than that I would suggest looking at Django as it will allow you to be more productive in producing code and also there are lots of tools out there that the community have developed over time.
Database:
Red.is is a good choice if you need a very fast no-sql db, also have a look at mongodb. If you require a multi-region DB I would suggest going with Cassandra or CouchDB due to the partitioned nodes. The image below might help you better decide which DB to use.
I am new at Server side,
but I have gotten a chance to design and implement a server that will cover around 2000~3000 client.
And I am thinking that I will use Python and Websocket, though I don't know this choice is appropriate.
In this point, I am curious on how to design the server.
I think there must be some architecture normally in use depending on capacity that server handles.
Otherwise, Could I use a Websocket server offered by some python package like Tornado or Django?
I hope that I can get any information on this.
Any advice?
I've had good experiences using haproxy in front of sockjs-tornado. Depending on how complex your server-side logic, routing, and persistence requirements are, you could write all your server endpoints using tornado and use SQLAlchemy to handle writes to a relational database or use a non SQL data store like Redis.
If your main requirement is real-time interactivity it might be worth investigating meteor as well.
One of solutions could be Pyramid, sockjs, gunicorn, and gevent. Nginx probably better suits to be a frontend than Apache, but of course if you do not have any lengthy processing on the backend, any decent asynchronous Python server with websocket and sockjs support (not sure about socket.io as an alternative) will work for you out of the box.
Lenghty processing should be offloaded to some queue workers anyway, so asynchronous server will fit the bill.
Just check whether all used datastore/database adapters are compatible with your server solution be it asynchronous or multi-threading.
I am trying to develop a python PyQt program that allow user to enter data about personal particulars and review them at a later time for processing purpose.
The program will be used by less than 5 persons at the same time. So, i am thinking to use Sqlite3 database as i believe it should be able to cope for that amount of traffic.
The frame work i have in mind is that, the clients will have their own copy of my python pyqt program on each machine. Whenever they perform any operations that required data read/write, it will connect to the server thorough internet and read/write from the sqlite.db on the server.
Basically, the server will be nothing but a remote data storage.
Currently, i am able to create the required GUI for data inputs by using various widgets like QlineEdit, QCombobox, QTextEdit and so on.
But i have never done network programming before, thus i have no idea how to implement a server that store the sqlite data file for my software. So my questions are
(1) if i have a PC that has 24/7 internet connection, how do i set it up so that it can act as a server that store the data file for my software?
(2)In what way can/should my program communicate to that server through internet.
Even if you can't give me exact answer, i would appreciate if you can provide me some information of so that i look up and study about it.
Any constructive advice will be appreciated.
FYI: all the PCs will be running windows XP SP3 32 bits.
There are different ways for a client to communicate with a server.
You can use
XMLRPC to create an object with methods that are called on the server side
You can use HTTP and REST for the server with the library requests or urllib for the client
For the latter you can use flask, bottle, django or other frameworks to create a website that serves the content
(tutorials)
You can use Pyro to remotely access the objects on the server. Useful if the clients should also communicate with eachother.
You can create your own protocol. You will learn a lot and value the other options.
The list is not complete
I suggest that you have a look at XMLRPC if that fits. For number 2 I can say that many APIs use such a HTTP-interface (twitter, github, facebok, google). It is easy to use also for other people.
Security is important. I am not an expert. If you send username and password in plain text then use SSL to encrypt the connection. If you can not get ssl to work with python you can use stunnel.
I'm interested in something based on Jabber but I didn't find a free/opensource one so I'm thinking of writing one.
I've installed a Jabber server and now thinking about the ways in which I can write the client. I'm thinking of one of either these two methods.
1) An ajax call made to a jabber script running on the webserver that takes care of connecting to the server. But then I thought because of the dependencies involved in the jabber client, it might end up consuming too much memory when a few clients connect.
2) The other method is to run a client running as a daemon that takes care of all the heavy lifting. This way I need to have only one instance of the client that sends a spoofed message (sender's name as that of whatever the user entered on the site). A simple script running on the webserver talks to this daemon over some sort of API (XMLRPC or Msgpack maybe?)
I think #2 is better but I'm not sure. Are there other ways I can implement this? I'm considering using Perl or Python for this.
Jabber is usually called XMPP nowadays, and there are dozens of clients and servers, something for every language. If you are using Javascript (you mention Ajax), you probably want Strophe. Most servers are modular, so you only load the features you need (consider Tigase, ejabberd, or xmpppy). Writing your own is even worse an idea than it sounds.
BOSH
Install prosody because it is really eaSily installed and has BOSH support built-in. You could skip this but then you need to find out how to use BOSH via ejabberd.
use strophe.js to implement this(using BOSH). New browsers support cross-domain request(CORS -> read Proxy-less BOSH part). The old browsers you could use proxy or use flash in the middle as proxy.
read Professional XMPP Programming with JavaScript and jQuery to learn strophe. It even has chapters explaining how to create chat.
Node.js
Or you could consider installing node.js to create your chat system using socket.io.
I have an XMPP server (likely — python, twisted, wokkel), which I prefer not to restart even in the development version, and I have some python module “worker” (which is interface to particular django project), which gets jid and message text and returns some response (text or XML, either way).
The question is, what would be the best way to connect them, considering that I may prefer to update the module part too often?
Another consideration is that it might be required to run multiple instances of “worker” for it all to be high-load-capable.
One possible way I see is implementing a thread in the server which checks if the module was changed and reload()s it if necessary.
The other way would be making something similar to fastcgi through sockets, although not HTTP-based.
My suggestion is:
Use RabbitMQ with XMPP adaptor.
Use Python carrot for AMQP since it can be used directly under Django.
I can't say that I understand all of your question, but the bit where you're asking how to connect django and twisted and multiple workers: I'd suggest using AMPQ. This gets you reliable message delivery, multiple consumers, persistence.
There's the txAMQP library for twisted.
https://launchpad.net/txamqp
A good primer to AMQP here, it's a good place to start:
http://blogs.digitar.com/jjww/2009/01/rabbits-and-warrens/