Assuming you have two bunch of servers, the first one dedicated to front and the other one, dedicated to process information from the fronts. What is the best way to transfer data from the fronts to the process servers;
I tried different techs on small amount of data:
tried to dump data into files and retrieve them from the process servers... that's ok very secure because you never lose your data, but it uses a lot of disc write capacity.
also tried sockets very cool
But sincerely I still don't know what is the best way to treat a huge data stream between servers.
Can someone point me in the right direction?
I would say the best option is to use a persistent queue, like RabbitMQ. That way if the receiving servers go down then your transfer is not lost and the transfer will simply continue when the receiving server pulls the data off the queue
Related
My stack is uWSGI, flask and nginx currently. I have a need to store data between requests (basically I receive push notifications from another service about events to the server and I want to store those events in the server memory, so client can just query server every n milliseconds, to receive latest update).
Normally this would not work, because of many reasons. One is a good deployment requires you to have several processes in uwsgi in production (and even maybe several machines to scale this out). But my case is very specific: I'm building a web app for a piece of hardware (You can think of your home router configuration page as a good example). This means no need to scale. I also do not have a database (at least not a traditional one) and probably normally 1-2 clients simultaneously.
if I specify --processes 1 --threads 4 in uwsgi, is this enough to ensure the data is kept in the memory as a single instance? Or do I also need to use --threads 1?
I'm also aware that some web servers clear memory randomly from time to time and restart the hosted app. Does nginx/uwsgi do that and where can I read about the rules?
I'd also welcome advises on how to design all of this, if there are better ways to handle this. Please note that I do not consider using any persistant storage for this - this does not worth the effort and may be even impossible due to hardware limitations.
Just to clarify: When I'm talking about one instance of data, I'm thinking of my app.py executing exactly one time and keeping the instances defined there for as long as the server lives.
If you don't need data to persist past a server restart, why not just build a cache object into you application that can do push and pop operations?
A simple array of objects should suffice, one flask route pushes new data to the array and another can pop the data off the array.
If StackOverflow is the wrong Exchange for this question, please help direct me to the correct one.
Short Version
What is the best design for a networking application in which one user transmits a constant, high-bandwidth stream of data to many other addresses? The solution must not require the uploader to duplicate the packets for each recipient and preferably will not transmit to users that have not been accepted by the transmitter.
Long Version
A friend and I have written an application that enables someone to transmit data in real time to one or more recipients that he wants to receive the data. I have designed the high-level application protocol to use UDP and to encode the data so that each packet can be lost without hurting the use of the rest. This solution requires managing sockets with each user and sending each packet to every user.
The problem here is that the stream can be very high bandwidth. The user can modify the settings for how high quality the data he is sending should be, and can end up sending 6 Mbps to each user. It is unfeasible to expect a user to pay his ISP enough to be allowed to upload such a stream to the preferred minimum of four other users at a time.
We need a way for the transmitter to send a packet exactly once and have each user receive a copy.
We have looked at multicasting. It may be what we need to use in the end, but we are concerned about the fact that anyone can join any group. It would be preferable to not allow users we do not want to see the data to not be allowed to join in. There is also the problem that if multiple transmitters happen to use the same group, viewers may find that they are receiving multiple streams' worth of data when they only want one.
My searching has revealed something IBM published over a decade ago called Explicit Multicast (Xcast) that looks perfect, but I have yet to find any information to determine whether this technology is commonly supported. Also, I have not yet seen whether it supports datagrams.
Does anyone know the best way to design an application that meets our needs?
Please keep in mind that we have no funds to support our project. Solutions need to be free.
Edit
In the summary above, I hinted at but failed to explicitly state that this is for a real-time application. The motivating drive behind the application is to keep the clients/recipients as close together in time as is possible. If packets are lost or arrive too late to be used in keeping the server and clients in phase, they need to be disregarded. That is why I designed the application protocol on top of UDP with independent data in each packet. Even if a client receives only one packet out of 300 for a given time step, it will use what it did get.
I think that I_am_Helpful's recommendation may be a good step in the right direction (or possibly the destination). I need to do some experimentation to determine whether using a system like Spread will work. However, I do not think I can budget more than additional 17 ms in transmission time.
If you can think of a system that enables sending unreliable datagrams to a specific group of users (like Spread) for a real-time application (unlike Spread, see p. 3), please let me know about it.
We need a way for the transmitter to send a packet exactly once and
have each user receive a copy.
In my limited knowledge, I would say that Reliable Multicasting appears to be one of the viable option for broadcasting in the group. I would like to mention that there are some of the possible Java API's* which could help you achieving the same :
JGroups Java API
The Spread Toolkit -> Spread consists of a library that user applications are linked with, a binary daemon which runs on each computer that is part of the processor group, and various utility and demonstration programs.
Appia
*NOTE : I have never worked with these API's.
It would be preferable to not allow users we do not want to see the
data to not be allowed to join in.
They do provide this feature, e.g., Spread supports thousands of groups with different sets of members. It also provides a range of reliability, ordering and stability guarantees for messages. JGroups can be used to create groups of processes whose members can send messages to each other. It also has facilities like group creation and deletion(Group members can be spread across LANs or WANs).
There is also the problem that if multiple transmitters happen to use
the same group, viewers may find that they are receiving multiple
streams' worth of data when they only want one.
When you could easily create multiple groups in the same network(using Spread,etc.), then, I believe that would no longer be an issue. It is your responsibility to declassify users into different groups.
I hope the given information helps. Good LUCK.
Via multicast you achieve exactly you want: sending each packet once, but authentication seems to be a concern for you.
One possible solution could be simetric cryptography, where the same key is used to encrypt and decrypt. Via TCP your clients connect to a server and fetch the multicast IP Address of the transmission and its associated key, then they join the multicast group and decrypt the incomming transmission.
If you accept a more flexible solution, you could have a server which sends a transmission in real time to a set of distributed servers. Your clients connect to one of these distributed servers via unicast, and after authentication is done, they are inluded in a list of receivers. Each distributed server sends each new transmission packet to each registered client via UDP. in ordinary situations your clients would have the same experience as if it was delivered in a multicast group, but the servers will spend far more bandwidth. Multiple transmission at a time will be allowed, so it could be good for you, and you can have more control, as clients can send signals to the servers, like PAUSE, and etc.
TL;DR
Is it appropriate for a (dedicated) web server to be sending many requests out to other servers every second (naturally with permission from said server)?
I'm asking this purely to save myself spending a long time implementing an idea that won't work, as I hope that people will have some more insight into this than me.
I'm developing a solution which will allow clients to monitor the status of their server. I need to constantly (24/7) obtain more recent logs from these servers. Unfortunately, I am limited to getting the last 150 entries to their logs. This means that for busy clients I will need to poll their servers more.
I'm trying to make my solution scalable so that if it gets a number of customers, I won't need to concern myself with rewriting it, so my benchmark is 1000 clients, as I think this is a realistic upper limit.
If I have 1000 clients, and I need to poll their servers every, let's give it a number, two minutes, I'm going to be sending requests off to more than 8 servers every second. The returned result will be on average about 15,000 characters, however it could go more or less.
Bearing in mind this server will also need to cope with clients visiting it to see their server information, and thus will need to be lag-free.
Some optimisations I've been considering, which I would probably need to implement relatively early on:
Only asking for 50 log items. If we find one already stored (They are returned in chronological order), we can terminate. If not, we throw out another request for the other 100. This should cut down traffic by around 3/5ths.
Detecting which servers get more traffic and requesting their logs less commonly (i.e. if a server only gets 10 logged events every hour, we don't want to keep asking for 150 every few minutes)
I'm basically asking if sending out this many requests per second is considered a bad thing and whether my future host might start asking questions or trying to throttle my server. I'm aiming to go shared for the first few customers, then if it gets popular enough, move to a dedicated server.
I know this has a slight degree of opinion enabled, so I fear that it might be a candidate for closure, but I do feel that there is a definite degree of factuality required in the answer that should make it an okay question.
I'm not sure if there's a networking SE or if this might be more appropriate on SuperUser or something, but it feels right on SO. Drop me a comment ASAP if it's not appropriate here and I'll delete it and post to a suggested new location instead.
You might want to read about the C10K Problem. The article compares several I/O strategies. A certain number of threads that each handle several connections using nonblocking I/O is the best approach imho.
Regarding your specific project I think it is a bad idea to poll for a limited number of log items. When there is a peak in log activity you will miss potentially critical data, especially when you apply your optimizations.
It would be way better if the clients you are monitoring pushed their new log items to your server. That way you won't miss something important.
I am not familiar with the performance of ASP.NET so I can't answer if a single dedicated server is enough. Especially because I do not know what the specs of your server are. Using a reasonable strong server it should be possible. If it turns out to be not enough you should distribute your project across multiple servers.
We are making an application involving a server(tomcat, apache, linux) and multiple mobile clients(Android, iPhone, Windows, Nokia J2ME).
Normally the clients and the server will communicate using http.
I would like to know the download and upload speeds of the client from the http request that it made.
Ideally I would not like to upload a file and download a file to come up with these speeds. I am assuming that there might be some thing at the HTTP protocol level that can give me this, or some lower layer of the network.
If only it were that simple.
Even where the bandwidth and latency of a network are very well defined, the actual throughput will be limited by the congestion window and where the end points are in establishing the slow start threshold. These can affect throughput by a factor of 20 or more.
There's nothing in HTTP which will provide metrics for these. Some TCP stacks will expose limited information about throughput (as used by iftop, iptraf).
However if you really want to gather useful metrics on HTTP throughput, then you need to start shoving data across the network - have a look at yahoo boomerang for an implementation.
If the http connection goes to the Apache server first, you can use Apache Bench to do all sorts of load testing. It comes with apache and can be invoked with something like the following.
Suppose we want to see how fast Yahoo can handle 100 requests, with a maximum of 10 requests running concurrently:
ab -n 100 -c 10 http://www.yahoo.com/
HTTP does not deal with connection speeds. Although I could imagine some solution that involves some HTTP (reverse) proxy that estimates speeds on a connection and sets custom headers to pass this info. You would also need to to associate stats of different connections with particular client. I have not seen yet a readily available solution for this.
Also note that
network traffic can be buffered or shaped so download speed may depend on amount of data transferred or previous load of network. So even downloading file would not be accurate.
Amount of data transferred depends on protocol level (payload wrapped in HTTP wrapped in gzip wrapped in TLS wrapped TCP). Which one do you want to measure? Or what do you want to achieve with this measured speed?
I've seen some Real User Monitoring (RUM) tools that can do this passively (they get a feed from a SPAN port or network TAP infront of the servers at the data centre)
There are probably ways of integrating the data they produce into your applications but I'm not sure it would be easy or perhaps given the way latency and bandwidth can 'dynamically' change on a mobile network that accurate.
I guess the real thing to focus on is the design of the app, how much data is travelling across the network, how you can minimise it etc.
Other thing to consider is whether you could offer a solution that allows some of the application to be hosted in the telco's POPs (some telcos route all their towers back to a central pop, others have multiple POPs)
Our client requirement is to develop a WCF which can withstand with 1-2k concurrent website users and response should be around 25 milliseconds.
This service reads couple of columns from database and will be consumed by different vendors.
Can you suggest any architecture or any extra efforts that I need to take while developing. And how do we calculate server hardware configuration to cope up with.
Thanks in advance.
Hardly possible. You need network connection to service, service activation, business logic processing, database connection (another network connection), database query. Because of 2000 concurrent users you need several application servers = network connection is affected by load balancer. I can't imagine network and HW infrastructure which should be able to complete such operation within 25ms for 2000 concurrent users. Such requirement is not realistic.
I guess if you simply try to run the database query from your computer to remote DB you will see that even such simple task will not be completed in 25ms.
A few principles:
Test early, test often.
Successful systems get more traffic
Reliability is usually important
Caching is often a key to performance
To elaborate. Build a simple system right now. Even if the business logic is very simplified, if it's a web service and database access you can performance test it. Test with one user. What do you see? Where does the time go? As you develop the system adding in real code keep doing that test. Reasons: a). right now you know if 25ms is even achievable. b). You spot any code changes that hurt performance immediately. Now test with lots of user, what degradation patterns do you hit? This starts to give you and indication of your paltforms capabilities.
I suspect that the outcome will be that a single machine won't cut it for you. And even if it will, if you're successful you get more traffic. So plan to use more than one server.
And anyway for reliability reasons you need more than one server. And all sorts of interesting implementation details fall out when you can't assume a single server - eg. you don't have Singletons any more ;-)
Most times we get good performance using a cache. Will many users ask for the same data? Can you cache it? Are there updates to consider? in which case do you need a distributed cache system with clustered invalidation? That multi-server case emerging again.
Why do you need WCF?
Could you shift as much of that service as possible into static serving and cache lookups?
If I understand your question 1000s of users will be hitting your website and executing queries on your DB. You should definitely be looking into connection pools on your WCF connections, but your best bet will be to avoid doing DB lookups altogether and have your website returning data from cache hits.
I'd also look into why you couldn't just connect directly to the database for your lookups, do you actually need a WCF service in the way first?
Look into Memcached.