IIS 7.0 503 errors with generic handler (.ashx) implementing IHttpAsyncHandler
OK. Fixed... many thanks to this post for clearing up a few details.
To eliminate the 503 errors required 3 different config changes:
machine.config:
<configuration>
...
<system.web>
...
<processModel enable="true" requestQueueLimit="100000"/>
IIS Manager > ApplicationPools > Advanced Settings
Queue Length : 65535
and finally (the missing piece of the puzzle), the command line:
appcmd.exe set config /section:serverRuntime /appConcurrentRequestLimit:100000
The web.config setting mentioned in the main post was irrelevant.
10000 concurrent connections, no problems. Thanks for help!
![spender](https://i.stack.imgur.com/SfY0b.png?s=256&g=1)
spender
I give my time here because I get so much more in return. Useful things I've written that might help you: blinq: a modern typescript reimplementation of linq-to-objects over iterable objects BkTree: a c# implementation of a Burkhard-Keller tree for indexing data in metric spaces. ComparerBuilder: A small c# library for easily creating complex IComparer<T> instances that compare multiple properties. See this answer for a rationale. ts-comparer-builder: A typescript library for creating complex "compareFunctions" for use with Array.sort. Very similar to ComparerBuilder above. ts-bin-heap: A typescript binary-heap implementation. Very handy for priority queues, which in-turn are very useful for search algorithms such as A*. Things I've written for other people: pShare client (see also) for Duality solutions: A cross-platform, blockchain and WebRTC based file-sharing platform, written with TypeScript, React and Redux, using electronjs.
Updated on June 05, 2022Comments
-
spender about 2 years
I'm running into some performance issues using a generic handler that implements IHttpAsyncHandler. At its simplest, the handler receives a GET request, and 20 seconds later ends the response after writing '< timeout / >' to the response.
When hammering the .ashx with 10000-20000 simultaneous requests, it fails with 503 server unavailable after precisely 5000 requests. When switching to synchronous mode, and ending the request immediately, the problem goes away.
I've tinkered with a number of settings, yet the only thing I've managed to acheive is lower the request threshold at which this error occurs.
Here's a rundown of the settings I've toyed with:
machine.config:
<configuration> ... <system.web> ... <processModel enable="true" requestQueueLimit="10000"/> ...
web.config:
<configuration> ... <system.web> ... <httpRuntime enable="true" appRequestQueueLimit="10000"/> ...
IIS Manager > ApplicationPools > Advanced Settings
Queue Length : 65535
Although I can't be sure, it seems like these settings work good and fine if the requests are synchronous, but when async, I can't seem to get beyond exactly 5000 requests before the server starts telling me to go away. If I set things lower (can't remember exactly which setting that would be from the above, but I've tried them all), then the 503 count goes up accordingly, but I can never stop it happening beyond 5000 when under serious load.
It seems that there a a number of settings scattered in a myriad of places that might affect this, but the 5000 seems fairly set in stone. I see here that appRequestQueueLimit cannot exceed 5000, but can find no further info about this, and wonder if this is misinformation.
Is there any kind of "flood-control" setting in IIS that might be limiting a single host to no more than 5000 requests? How can I get IIS to handle more that 5000 concurrent asynchronous requests?
Edit2: Are there any counters or other indicators of which limit might be being exceeded, and how would I investigate further?
Edit: Here's the loadgenerator code:
using System; using System.Net; using System.Threading; namespace HammerTime { class Program { private static int counter = 0; static void Main(string[] args) { var limit = 5000; ServicePointManager.DefaultConnectionLimit=limit; for (int i = 0; i < limit;++i ) { StartWebRequest(i.ToString()); } Console.ReadLine(); } private static void StartWebRequest(string channelId) { string uri = "http://spender2008/test/Test.ashx?channel="+channelId; HttpWebRequest request = (HttpWebRequest) WebRequest.Create(uri); request.BeginGetResponse(responseHandler, request); } private static void responseHandler(IAsyncResult ar) { try { HttpWebRequest state = (HttpWebRequest)ar.AsyncState; HttpWebResponse response = (HttpWebResponse)state.EndGetResponse(ar); } catch(Exception e) { Console.WriteLine(e.Message); } finally { Console.WriteLine(Interlocked.Increment(ref counter)); } } } }
-
MordechayS almost 14 yearsThanks for sharing the solution, I was getting the blank white 503 screen of death when a site had a lot of traffic for some reason, the appcmd fixed it