I was wondering how can I find the "number of connections limit" for a web server.
Most of the cases I encountered it is limited to 6 connections (Meaning I can have 6 connections to this webserver working at the same time).
Is there any request I can send over HTTP?
Could you be more precise ? What kind of server ? Any ? For which OS ?
If it's an Apache http server, you should have a look in the settings file (should be /etc/httpd/conf/httpd.conf under Linux). Search for MaxClients option.
For example, I use a small apache server at home which can process 300 simultaneous requests (connections).
EDIT :
I think you won't be able to get the server specifications. You should try to overload it in order to guess its limits.
There's nothing like this in the HTTP standard, it aims to isolate HTTP requests from each other as much as possible. There might be a server-specific way to query this.
Depending on the architecture of your server, there could be a far greater number of TCP connections accepted than worker threads generating the HTTP responses, so you need to ask yourself what exactly you are interested in, and then just measure it with jmeter.
Related
With HTTP/1.0, there used to be a recommended limit of 2 connections per domain. More recent HTTP RFCs have relaxed this limitation but still warn to be conservative when opening multiple connections:
According to RFC 7230, section 6.4, "a client ought to limit the number of simultaneous open connections that it maintains to a given server".
More specifically, besides HTTP/2, these days, browsers impose a per-domain limit of 6-8 connections when using HTTP/1.1. From what I'm reading, these guidelines are intended to improve HTTP response times and avoid congestion.
Can someone help me understand what would happen with congestion and response times if many connections were opened by domain? It doesn't sound like an HTTP server problem since the amount of connection they can handle seems like an implementation detail. The explanation above seems to say it's about TCP performance? I can't find any more precise explanations for why HTTP clients limit the number of connections per domains.
The primary reasoning for this is resources on the server side.
Imagine that you have a server running Apache with the default of 256 worker threads. Imagine that this server is hosting an index page that has 20 images on it. Now imagine that 20 clients simultaneously connect and download the index page; each of these clients closes these connections after obtaining the page.
Since each of them will now establish connections to download the image, you likely see that the connections increase exponentially (or multiplicatively, I suppose). Consider what happens if every client is configured to establish up to ten simultaneous connections in parallel to optimize the display of the page with images. This takes us very quickly to 400 simultaneous connections. This is nearly double the number of worker processes that Apache has available (again, by default, with a pre-fork).
For the server, resources must be balanced to be able to serve the most likely load, but the clients help with this tremendously by throttling connections. If every client felt free to establish 100+ connections to a server in parallel, we would very quickly DoS lots of hosts. :)
We are trying to do Load test on our servers, for this we are currently using JMeter.
However we have decided to use golang's concurrency model to create simultaneous http requests to the server and perform the load test.
Is there any limitations on how many http requests or tcp connections a machine can open/send to any other machine, is there any way to find this number?
Edit----
We need this number since this will help us identify how many http request can be sent simultaneously to the server
Thanks
Is there any limitations on how many http requests or tcp connections a machine can open/send to any other machine, is there any way to find this number?
Yes. When connecting to a single target, you are limited by the number of outbound ports, which is 65535. In practice somewhat less, as not all ports are available for use as outbound ports.
We need this number since this will help us identify how many http request can be sent simultaneously to the server
From any one machine. It has nothing to do with the maximum number of connections from different machines.
I have an ASP.NET Web API application running behind a load balancer. Some clients keep an HTTP busy connection alive for too much time, creating unnecessary affinity and causing high load on some server instances. In order to fix that, I wish to gracefully close a connection that is doing too much requests in a short period of time (thus forcing the client to reconnect and pick a different server instance) while at same time keeping low traffic connections alive indefinitely. Hence I cannot use a static configuration.
Is there some API that I can call to flag a request to "answer this then close the connection" ? Or can I simply add the Connection: close HTTP header that ASP.NET will see and close the connection for me?
It looks like the good solution for your situation will be the built-in IIS functionality called Dynamic IP restriction. "To provide this protection, the module temporarily blocks IP addresses of HTTP clients that make an unusually high number of concurrent requests or that make a large number of requests over small period of time."
It is supported by Azure Web Apps:
https://azure.microsoft.com/en-us/blog/confirming-dynamic-ip-address-restrictions-in-windows-azure-web-sites/
If that is the helpful answer, please mark it as a helpful or mark it as the answer. Thanks!
I am not 100% sure this would work in your situation, but in the past I have had to block people coming from specific IP addresses geographically and people coming from common proxies. I created an Authorized Attribute class following:
http://www.asp.net/web-api/overview/security/authentication-filters
In would dump the person out based on their IP address by returning a HttpStatusCode.BadRequest. On every request you would have to check a list of bad ips in the database and go from there. Maybe you can handle the rest client side, because they are going to get a ton of errors.
Write an action filter that returns a 302 Found response for the 'blocked' IP address. I would hope, the client would close the current connection and try again on the new location (which could just be the same URL as the original request).
After working a bit with cookie related problems . Something struck me .
Why do we need to do all these gimmicks of maintaining cookies or session data ?
Was wondering if this is so common why cant this be done by default by system ?
I am lazy ...
But I remember that I don't do this job of maintaining session data in a number of places . For example SSH . When I do ssh I just do ssh and I am connected . I am not bothered of all these details like session . System takes care .
Then why should I do these things in web sites .
Ya then opened college networking book by Forouzan . Started reading and found that http was a stateless protocol . Ssh is stateful .
Ahh ...
Then why are we using http protocol . If not why not use some other protocol which is stateful .. Or why don't we change http to stateful . Are we loosing anything out of doing this ? Why is it not done ?
I searched at many places but could not get a solid convincing answer . But every one said this "To make http protocol simple " .
I cannot understand how this makes simple .I don't know the magnitude to which it is simplified by keeping http stateless ?
Can you direct me to some books which can explain this final question how much http is simplified by keeping it stateless ?
If not Can you give an answer so easy to understand that even a 6 year child can understand .
AFAIK, the main reason is to reduce load on web servers. As it stands, when you make a HTTP connection, web server serves your request and then forgets about you, which allows it to free the resources. If HTTP was stateful, web servers would have to maintain (hundreds of) thousands simultaneous connections, which would require extremely large hardware resources.
It is worth noting that HTTP 1.0/1.1 (default in 1.1) has a Connection: Keep-Alive header that will keep the TCP socket open for subsequent requests. One could keep the socket open forever (at least until it is broken or closed, but not timed out) in theory, although they would need to be mindful of resource usage. Apache automatically closes the TCP connection, but with a custom server implementation this isn't a problem.
From Wikipedia: HTTP persistent connection:
Disadvantages:
For services where single documents are regularly requested (for example, image hosting websites), Keep-Alive can be massively detrimental to performance due to keeping unnecessary connections open for many seconds after the document was retrieved.
Due to increased complexity, persistent connections are more likely to expose software bugs in servers, clients and proxies.
However, it also states:
Advantages:
Lower CPU and memory usage (because fewer connections are open simultaneously).
Reduced network congestion (fewer TCP connections).
Reduced latency in subsequent requests (no handshaking).
These (dis)advantages have been recognized, which is why there's this thing called a WebSocket.
HTTP was originally intended for document access, where through HTML these documents could be linked to each other. You connect to the server, request a document, download it and the connection would be closed by the server.
I don't think sir Tim Berners-Lee foresaw the kind of applications built on top of HTTP we have nowadays, that's why there's being worked on WebSockets and HTTP 2.0, who try to mitigate some of the issues that rise from HTTP's stateless nature.
I am trying to create a Web Server of my own and there are several questions about working of Web servers we are using today. Questions are:
After receiving a HTTP request from a client through port 80, does server respond using same port 80?
If yes then while sending a large file say a pic in MB's, webserver will be unable to receive requests from other clients?
Is a computer port duplex or simplex? (Can it send and receive at the same time)?
If another port on server side is used to send response to client, then (if TCP is used, which is generally used), again 3-way handshaking will be done which will be overhead...
http://beej.us/guide/bgnet/output/html/singlepage/bgnet.html here is a good guide on what's going on with webservers, although it's in c but the concepts are all there. This will explain the whole client server relationship as well as some implementation details.
I'll just give a high level on what's going on:
Usually what happens is when your server gets a new request that comes in it creates a fork that will process it, that way you are not bogged down by each request, when the request comes in the child process is handed a new file to write to(again this is all implementation details).
So really you have one server waiting for requests and for each request it received it spawns a child to process to deal with this request. I'm sure there are much easier languages to implement this stuff than c(I had to do both a c and java server serving to either one in my past) but c really gets you to understand the things that are going on and I'm betting that is what you are looking for here
Now there are a couple of things to think about:
how you want the webserver to work. The example explains the parent child process.
Do you want to use tcp/UDP there are differences in the way to payload gets delivered.
You don't have to connect on port 80. that's just the default for web.
Hopefully the guide will help you.
Yes. The server sends the response using the TCP connection established by the client, so it also responds using the same port. The server can handle connections from multiple clients using the same port because TCP connections are identified by (local-ip, local-port, remote-ip, remote-port), so the server can even handle multiple connections from same client provided that the source ports are different.
There are different techniques you can use to be able to serve multiple clients at the same time. These include
using multiple processes or threads: when one is busy serving a client the others can serve other clients.
using events: the server listens for events from the OS: when it can write a block of data to a connection it writes it, when a new client connects it accepts the connection, ...
Frequently both approaches are be combined.
A TCP connection is duplex: you can send and receive at the same time. The HTTP protocol is based on a simple request-response model though: at any given time only one party is "talking."