First time post here, so forgive me for any bad etiquette/format.
I will preface by saying:
I have (over the last few months) been developing an iOS app for work. To be more specific, I am developing an inventory app to track bar inventory (liquor, beer, wine, etc). I can give more specifics on request if needed. I have most of the functionality done, only a couple more things I would like to implement. Eventually I will be porting it to Android as well.
At the moment, I have the model objects being archived to the local filesystem for saving and loading of data. However, my goal would be to database the model objects with the ability to display the information on a webpage. My logic is that no matter where the user is, he/she will be able to sign in to a service using a username and password, and view correctly formatted current/past inventories online. This is to allow the ability for a bartender to record the inventory, and have the bar manager view the inventory instances without having to have the physical device that recorded the inventory in his/her possession.
So here is my question:
Without being too general, what kind of service would I need to pull this off? I have a good amount of relevant front-end experience, specifically with iOS, Objective-C, HTML and CSS. However, I have ZERO experience on the back-end. I have researched around the internet, and I am aware of things such as cloud databases, web hosting and MySQL, etc. However, I cannot seem to find a definitive answer without asking my specific question. I suppose I would just like to be pointed in the right direction before investing money and time into a service that may prove useless to my cause.
Any resources and help would be greatly appreciated. Thank you!
There's not a definitive answer and you have a lot of options.
For me, the simplest is to set up a server with a database incorporated (mysql for example) and with a web service (written in PHP for example) that manages the database and queries on that.
Online you can find tons of guide on how to write a script in PHP that manages a database:
http://www.freewebmasterhelp.com/tutorials/phpmysql/2
For the iOS part you can follow also this guide:
http://www.techrepublic.com/blog/software-engineer/create-your-own-web-service-for-an-ios-app-part-one/
Good luck!
I've been looking into sockjs-tornado recently and am working on a chat function for a social networking site. I'm trying to get a feel for common methods used in building scalable multiroom chat functionality. I'll outline a couple of the methods I've thought of and I'd like to get feedback. What methods are used in the real world? What are the advantages and disadvantages to these methods?
Prereqs:
running tornado
using sockjs-tornado lib
sockjs-client lib for js
Everything else is open.
Methods I've considered:
For loop
This seems like the simplest way to go. You create a user class that subscribes to certain room classes. The user sends a message class that contains a room id and the server redirects the message in the loop only to users that have subscribed to that room. This seems to me to be by far the worst because the complexity is obviously at least linear. (Imagine 500 users connected at once to 5 chat rooms each.)
Multi-tasking/multiple server instances
This also seems like a bad idea because you could have 500 server instances running at any time on... different ports? I'm really not sure on the implementation of this method.
Native support
Now granted, a lot of libraries have this built in such as socketio. However that's not an option due to the sole node.js support. (I'm on tornado server.) Socks in particular does not have built in support for multiple "rooms".
Conclusion
I'm looking for resources/case studies, and industry standards. Any help would be appreciated.
I would just use a message queue server like RabbitMQ with a fanout exchange as each "chat room".
You can see an example of using a fanout exchange in Python here.
The Pika AMQP library works with Tornado, too.
The advantage with using a message queueing system is that you can have users connected to different Tornado processes on different servers while still being in the same "room", giving you high availability on the HTTP layer.
RabbitMQ also has HA capabilities (although not the greatest).
I'm planning to setup an scalable architecture capable of providing web services on a REST interface where JSON will be sent as a result.
The web services will be quite simple for a CRUD web 2.0 app.
I think javascript (nodejs + mongodb) is a good choice for the following reasons:
Easy to find javascript developers
Good performance
Easy to scale
Shared logic/language or possible reuse of code between database query language, back-end and web-client.
There are testing and logging frameworks for node
By the examples I've seen node seems light in terms of the lines of code needed to implement web services.
Questions:
I think of scaling a node app which supplies a web service as having
a central node which will be routing/balancing charge to each of the
node instances. Which will also help doing seamless updates, is
there any piece of software already implemented which can fit that
task?
Please point all the disadavantages or other advantages you find in this back-end stack
If you feel this question opens too much of a debate and doesn't fit the stackoverflow policy please indicate a forum where I could get feedback.
Any other good persistence choices other than MongoDB? Mainly this choice comes from the javascript query language and JSON schemas.
Regarding your "router" piece:
Since your REST api will be composed of HTTP requests, it's common practice to use a high-speed proxy such as NGINX or HAProxy to distribute requests among the many servers who actually perform the work (in your case, NodeJS servers). This generally works well and allows easy scaling and failover.
What problem do MOM (Message Oriented Middleware) solve? Scalability? Integration?
In which domain are they typically used and in which domains are they typically not used?
For example, say, is Google using such solution for it's main search engine or to power GMail?
What about big websites like Walmart, eBay, FedEx (pretty much a Java shop) and buy.com (pretty much an MS shop)? Does MOM solve a need there?
Does it make any sense when you're writing a Webapp where you control the server-side and have an homogenous environment (say tens of Amazon EC2 instances all running Linux + Java JVMs) there and where the clients are, well, Web browsers?
Does it make sense for desktop apps that need to communicate with a server?
Or is it 'only' for big enterprise stuff where you typically have a happy mix of countless of different systems that needs to communicate in a way or another?
I'm a bit confused as to what they're useful for and I think that with example of where they're appropriate and where they're not appropriate I could better understand their use.
This is a great question.
The main uses of messaging are: scaling, offloading work, integration, monitoring, event handling, routing, networking, push, mobility, buffering, queueing, task sharing, alerts, management, logging, batch, data delivery, pubsub, multicast, audit, scheduling, ... and more. Basically: anything where you need data but don't want to make a database request. (Caching is another, longer story).
Another way of looking at this is to notice that many applications used to be built by assuming that users (people) would perform actions that would be fulfilled by executing a transaction on a database (including reads, writes). But today, many actions are not user-initiated. Instead they are application-initiated. For example "tell me when the book that I want to buy is in stock". The best way to solve this class of problems is with messaging of some sort. Whether you call it middleware or web push or real time salad dressing does not matter. It's all messaging.
When you enable applications to initiate or react to events, then it is much easier to scale because your architecture can be based on loosely coupled components. It is also much easier to integrate those components if your messaging is based on a stable, scalable, serviceable tool, preferably using open standard APIs and protocols.
I hope this helps. We try to maintain a list of useful links about messaging here
Please get in touch with questions and comments on any of this, we are dead easy to find.
To address your specific questions:
In which domain are they typically used and in which domains are they typically not used?
Like databases, messaging systems crop up everywhere.
For example, say, is Google using such solution for it's main search engine or to power GMail?
Google uses a lot of home grown technology, but a lot of their open source contributions and known use cases suggest that messaging is (or should be) central to some of the main services.
What about big websites like Walmart, eBay, FedEx (pretty much a Java shop) and buy.com (pretty much an MS shop)? Does MOM solve a need there?
Very much so.
An example use case is scaling web page requests. When the user makes a web request, the web server puts it onto a queue for background processing. This means that the web server can keep working while the request is processed. It also means that the web server does not need to know how the request is handled, making system maintenance, upgrade and rollback much simpler because the main parts are 'decoupled'.
So, anyway, the web request gets processed by a back end service, or possibly by many services, eg 'look up book titles', 'draw shopping cart', 'get advertisement', 'check user account'... Finally all the results get put onto another queue, ready for collection and user response by the web server. Typically the system will include a timeout of around 100ms so that any late requests just get thrown away. The user sees anything that got processed in the time interval. This is one reason why some large ecommerce sites have pages that appear to load in stages.
There are many more use cases...
Does it make any sense when you're writing a Webapp where you control the server-side and have an homogenous environment (say tens of Amazon EC2 instances all running Linux + Java JVMs) there and where the clients are, well, Web browsers?
Definitely. If you have an unknown, or unbounded, number of users, server side instances, and application latencies, then it makes sense to use messaging, even if just as a scalable substrate for non-blocking RPC.
Does it make sense for desktop apps that need to communicate with a server?
In lots of cases. One very common case is when the server pushes events to the desktop app, eg game event, tweets, price feeds in finance, system alerts....
Or is it 'only' for big enterprise stuff where you typically have a happy mix of countless of different systems that needs to communicate in a way or another?
Definitely not only for those 'legacy integration' cases but they are important too. At RabbitMQ, the biggest customers we have in terms of pure scale or message volume are cloud providers and big web application providers.
I will answer only one answer, from prior experience - take a look at this middle-ware that is employed by big companies here - middle-ware has one purpose - to glue dis-connected systems (written in disparate languages) together so that they can interact with one another and streamline the business process - Entera as I have had experience with, creates a middle layer in which the unix box using processes written in C, interact with the mainframe system (DB2, COBOL) via a front-end written in PowerBuilder (I am not naming the company!).
From the description I have given, Entera is a middle-ware which hosts a number of things - smooth integration of the flow of data regardless of the endian format, ability for different languages to talk to the middle-ware broker (a broker is a CORBA or DCE like process, that conforms to 'The Open Group) that listens on a particular port) and is specified by an IDL which makes a process appear to be local - if you understand the terminology used in Remoting under Microsoft's .NET Framework, you are not far off the mark! The middle-ware generates stubs which are linked at compile-time and manages the creation of the process, hosting it off a port, multi-threading at run-time, and also, the modern front-ends (such as .NET, Java, PowerBuilder even the unspeakable VB6...ok...VB.NET for the purists out there) can interact by opening a connection to the specified port on a particular IP address, and using the stubs generated, can interact with it directly.
Obviously, from what was described you can see how the legacy systems can have new life breathed into it and thus scalability of the process, the major downside of this is the cost factor which can run into thousdands of dollars. Big companies who uses mainframes as their back-end processing systems for billing/invoicing, who generate a huge revenue can obviously afford such an expensive product - to them it would seem like throwing pennies into a pool of water...because of the use of middle-ware which prolongs the business process, and breathe new life into it, can extend the business by a good number of years into the future without worrying about 'legacy' tag attached to it.
Incidentally, I carried this out as part of my thesis for my BSc. in Information Systems which covered this commercial front-end. There was an open source version of the middle-ware available on sourceforge called FreeDCE, but development efforts have declined or stopped.
Edit:
#cocotwo: That is exactly what middle-ware does as you said it is a plumbing tool...message oriented middle-ware is not really heard of AFAIK because I would imagine, the processes (functions) would need to be called as if they are locally visible within the application domain of the front-end to make it easy to interact with.
Using messages may have its advantages over RPC calls in that the messages are queued in a safe-holding area in the event that a network disconnection occurs - there may be some data caching going on within that aspect to allow the front-end to continue regardless...it would be useful in the instances of 'updating a status of a particular billing/invoice number' - a one-way write-data to the back-end via the middle-ware.
Ok, big companies would have advanced systems infrastructure in that technicians are constantly around the clock to ensure a smooth delivery of data-flow so that would have to be factored in. The company that I worked with had IBM Global Support contract to fulfill in order to ensure a maximum uptime 99% with 6 nine's after the decimal point...with hot-swapping/balanced-clusters/mirroring systems in place...
Whereas with RPC, if the disconnection occurs, the front-end would have to be restarted or would have to handle the disconnection event. It really depends if the message-queueing middle-ware handles each message in real-time and pass back results to the front-end immediately...
This is where each (Message-queueing and RPC related middle-ware) have their strengths and weaknesses...and also the cost mitigation factor such as support, maximum up-time, development efforts and training - that's a biggie here as middle-ware are really proprietary (despite following the 'The Open Group' layout/standards) and complex to setup and to glue the whole thing together via scripts.
Good answers and discussion here. Our consulting team has two preferred "messaging" solutions: RabittMQ and NXTera a high speed RPC middleware, the contemporary version of Entera mentioned above. My partners and I have developed several solutions using RabittMQ, it is the best tool available in that space right now. Additionally, I happen to work for the company that makes NXTera/Entera.
From experience I can clearly say that both of these products meet the need for reliability and low maintenance as discussed above. There are situations where a messaging service, like RabittMQ, is the right choice -- where Publish and subscribe, certified delivery, Queuing or store-and-forward are required.
In other cases, RPC's (remote procedure calls) are the best and fastest solutions for transactional and distributed processing for enterprise or cloud-based applications. When it is right to use an RPC, but SOAP/.NET (yes these are RPC implementations) are too slow, expensive or complex, a lightwieght high speed RPC middleware like NXTera/Entera is the right choice for us.
There is some use case overlap between RPC middleware and message oriented middleware, and where there are you can use either successfully. But both are strong and dependable choices.
The large companies I work with use both RPC and MoM side-by-side. As far as Internet companies, Google (Protocol Buffers) and Facebook (Thrift) show that RPC's have a roll to play in modern web and cloud-based development.
There is previous little on the google on this subject other than people asking this very same question.
How would I get started writing my own firewall?
I'm looking to write one for the windows platform but I would also be interested in this information for other operating systems too.
For Windows 2000/XP there is an article with examples on CodeProject Developing Firewalls for Windows 2000/XPFor Vista I think you will need to use Windows Filtering Platform
This question is alarmingly similar to those asking how to write an encryption algorithm. The answers to both should end in gentle reminders about industry standard solutions that already:
embody years of experience and constant improvement,
are probably far more secure than any home-grown solution, and
account for ancillary requirements, such as efficiency.
A firewall must inspect every packet efficiently and accurately, and it therefore runs within the OS kernel or network stacks. Errors or inefficiencies jeopardize the security and performance of the entire machine and those downstream.
Building your own low-level firewall is an excellent exercise that will provide an education across many technologies. But for any real application, it's much safer and smarter to build a shell around the existing firewall API. Under Windows, the netsh command will do this; Linux uses netfilter and iptables. Googling any of these will point you to lots of theory, examples, and other helpful information.
So, to get started, I'd brush up on TCP/IP (specifically, the header information: ports and protocols), then learn about the various types of attacks and how to detect them. Learn about each operating system of interest and how it interacts with the network stacks. Finally, think about administration and logging: how will you configure your firewall and trace packets through it to ensure it's doing what you want it to do?
Good luck!
The usual approach is to use API hooking. Google can teach you that. Just hook all important networking stuff, like connect's and listens's, and refuse what you want.