I have a web application that builds web-pages using agent (it's written in LS and we use [print html] to output HTML) and from time to time I see an error as below.
02-11-2020 10:00:18 HTTP Web Server: Agent did not complete within configured time limit [/path-to-database.nsf/web?openagent] Anonymous
02-11-2020 10:00:18 HTTP Server: Execution time limit exceeded by Agent '(Web)|Web' in database '/path-to-database.nsf'. Agent signer 'signer name'.
As a result HTTP task stuck so I have to restart it, but that means I have to monitor it all the time.
It does not seems to be related to agent time execution, otherwise I would have this issue constantly.
The activity does not seems to be the issue as well, according to google analytics it's around ~50 active users.
I doubt [Server Tasks\Agent manager] will help, because agent runs under HTTP task.
Does anybody know how to figure out what is the reason of such issue and where I have to dig to fix it.
Update
Domino version 11.0
The agent is triggered by anonymous visitor and does some relatively heavy computation to construct HTML response (loops and lookups are present, but I'm sure all loops ends properly, without infinitive run).
I guess settings for HTTP Agents are under this section (so 2 mins).
Web Agents and Web Services
Run web agents and web services concurrently? Enabled
Web agent and web services timeout: 120 seconds
In general request takes between 300ms-1 second, however there are some heavy pages with 1-5 seconds (but nothing like 10 seconds or more).
I notice the error only when we get more than 50 active users (who activity open new pages and thus trigger the agent).
I guess Richard is right and there must be some condition when agent stuck (maybe related to views update or some background process).
For now I simply restart HTTP to get this issue fixed (for some time).
So my question could be re-phrased to:
What can cause delay of the agent that build web page (taking into account it's related to 50-100 active users).
Thanks a lot :-)
I am hosting a RESTful API and my problem is that every first inbound request after a certain time will take about three seconds, compared to the normal ~100ms.
What I find most interesting is that it is always takes exactly 3100 to around 3250 milliseconds, not more and not less. So it seems pretty intentional to me.
I've already debugged the API and everything runs pretty much instantly except for one thing and that is this three second delay before my API even starts to receive the request.
My best guess is that something went wrong either in Apache or the DNS resolution but I don't know what exactly causes it (that's why I'm asking this question).
I am using the Apache ProxyPass like this:
ProxyRequests off
Timeout 54
ProxyTimeout 5400
ProxyPass /jokeapi http://localhost:8079
ProxyPassReverse /jokeapi http://localhost:8079
I'm using the Cloudflare/APNIC DNS gateway servers 1.1.1.1 and 0.0.0.0
Additionally, all my requests get routed through a Cloudflare SSL proxy before even reaching my network.
I've even partially rewritten the API so it responds with ReadStreams instead of loading the files into RAM and serving it at once but that didn't fix the problem.
My question is how I can fully debug the route a request takes and see precisely where this 3 second delay comes from.
Thanks!
PS: the server runs on NodeJS
I think the key is not related to network activity, but in the note that after a period of idle activity the first response to the API in a while requires slightly over 3 seconds. I am assuming that follow up actions are back to the 100ms window.
As you are using localhost, this is not a routing issue. If you want, you can just as easily use loopback, 127.0.0.1, to avoid a name resolution hit, but such a hit on a reserved hostname would be microseconds.
I suspect that the compiled version of your RESTful function has aged out of the cache for your system. The first hit after a period of non-use time then requires a recompile, and so long as the compiled instructions are exercised for a period of time they will remain in cache and contoninue to respond in the 100ms range. We observe this condition quite often in multiuser performance testing after cold boots of systems (setting initial conditions). Ramp-ups of the test users take the hit for the recompiles of common code before hitting the time under full load.
Another item to strike back at the network side of the house, DNS timeouts and bind cache entries tend to be quite long, usually significant portions of a day or even longer. Even so, the odds that a DNS lookup for an item which has aged out of the bind cache would not add three seconds to your initial connection time.
Every day at about 3:00PM-4:00PM GMT the response times start to increase (no memory increase or CPU increase)
There is a azure availability test going to server every 10 minutes.
As this is a dev site there is no traffic to it other than me (at the odd time) and the availability test
I log to a variable internally the startup time and this shows that the site is not restarting
The first request via a browser when this starts happening is very slow (2 minutes - probably some timeout).
After that it runs perfectly. That seems like the site is shutting down and then starting up on first request, but the pings are keeping it alive so the site is not shutting down (as far as I know)
On the odd log entry I get - I seem to be getting 502 errors - but I can't confirm this as the FEEB logs are usually off at this time.
FREB logs turn off automatically after 1 hour and as this is the middle of the night for me (NZDT) - I don't get a chance to turn on.
See attached images - as you can see the response times just increase at same time
Ignore the requests where they are above 20 - thats me going to it via browser
I always check the azure dashboard BEFORE viewing site in browser
Just got this error (from web browser randomly - keep accessing the same page:
502: The specified CGI application encountered an error and the server terminated the process.
Other relevant Info (Perhaps):
I initially had the availability test ping going to a ping endpoint /ping that only returned a 200 and empty string when I noticed this happening
It now points to the sites homepage to see if it changed anything - still the same.
Assuming the database is not the issue as the /ping endpoint doesn't touch the database - just a straight controller return.
Internal Exception handling is catching nothing
Service: Azure Free Web App (Development)
There are no web jobs or timed events on this site
Azure Dashboard Initial
Current tests:
Uploading as new site to a Basic 1 Small
Restarting dev site 12 hours before issues (usually 20 hours before)
Results:
Restarting free web-app 12ish hours before issue - same result at same time - so its not the app slowly overloading or it would me much later
Basic 1 Small: no problems - could it be something with the dev server ?
Azure Dashboard From Today
Observations:
Same behavior with /ping endpoint (just return empty string 200 Ok) and Main home page endpoint (database lookups [w/caching] / razer)
If anyone has any ideas what might be going on - I would very much appreciate it
:-)
Update:
It seems to of stopped (on its own) about 11/1/2016 1:50:49 AM GMT - my internal timestamp says it restarted - and then the errors started again same time as usual. Note: no-one is using the app. The basic 1 Small Server is still going fine.
Sorry I can't add anymore images (not enough rep)
By default, web apps are unloaded if they are idle for some period of time, which could cause the web site slow response during this period of time. Besides, this article is about troubleshooting HTTP "502 Bad Gateway" error or a HTTP "503 Service Unavailable" error in Azure web apps, you could read it. And from the article we could know scaling the web app could mitigate the issue.
In my company we experienced a serious problem today: our production server went down. Most people accessing our software via a browser were unable to get a connection, however people who had already been using the software were able to continue using it. Even our hot standby server was unable to communicate with the production server, which it does using HTTP, not even going out to the broader internet. The whole time the server was accessible via ping and ssh, and in fact was quite underloaded - it's normally running at 5% CPU load and it was even lower at this time. We do almost no disk i/o.
A few days after the problem started we have a new variation: port 443 (HTTPS) is responding but port 80 stopped responding. The server load is very low. Immediately after restarting tomcat, port 80 started responding again.
We're using tomcat7, with maxThreads="200", and using maxConnections=10000. We serve all data out of main memory, so each HTTP request completes very quickly, but we have a large number of users doing very simple interactions (this is high school subject selection). But it seems very unlikely we would have 10,000 users all with their browser open on our page at the same time.
My question has several parts:
Is it likely that the "maxConnections" parameter is the cause of our woes?
Is there any reason not to set "maxConnections" to a ridiculously high value e.g. 100,000? (i.e. what's the cost of doing so?)
Does tomcat output a warning message anywhere once it hits the "maxConnections" message? (We didn't notice anything).
Is it possible there's an OS limit we're hitting? We're using CentOS 6.4 (Linux) and "ulimit -f" says "unlimited". (Do firewalls understand the concept of Tcp/Ip connections? Could there be a limit elsewhere?)
What happens when tomcat hits the "maxConnections" limit? Does it try to close down some inactive connections? If not, why not? I don't like the idea that our server can be held to ransom by people having their browsers on it, sending the keep-alive's to keep the connection open.
But the main question is, "How do we fix our server?"
More info as requested by Stefan and Sharpy:
Our clients communicate directly with this server
TCP connections were in some cases immediately refused and in other cases timed out
The problem is evident even connecting my browser to the server within the network, or with the hot standby server - also in the same network - unable to do database replication messages which normally happens over HTTP
IPTables - yes, IPTables6 - I don't think so. Anyway, there's nothing between my browser and the server when I test after noticing the problem.
More info:
It really looked like we had solved the problem when we realised we were using the default Tomcat7 setting of BIO, which has one thread per connection, and we had maxThreads=200. In fact 'netstat -an' showed about 297 connections, which matches 200 + queue of 100. So we changed this to NIO and restarted tomcat. Unfortunately the same problem occurred the following day. It's possible we misconfigured the server.xml.
The server.xml and extract from catalina.out is available here:
https://www.dropbox.com/sh/sxgd0fbzyvuldy7/AACZWoBKXNKfXjsSmkgkVgW_a?dl=0
More info:
I did a load test. I'm able to create 500 connections from my development laptop, and do an HTTP GET 3 times on each, without any problem. Unless my load test is invalid (the Java class is also in the above link).
It's hard to tell for sure without hands-on debugging but one of the first things I would check would be the file descriptor limit (that's ulimit -n). TCP connections consume file descriptors, and depending on which implementation is in use, nio connections that do polling using SelectableChannel may eat several file descriptors per open socket.
To check if this is the cause:
Find Tomcat PIDs using ps
Check the ulimit the process runs with: cat /proc/<PID>/limits | fgrep 'open files'
Check how many descriptors are actually in use: ls /proc/<PID>/fd | wc -l
If the number of used descriptors is significantly lower than the limit, something else is the cause of your problem. But if it is equal or very close to the limit, it's this limit which is causing issues. In this case you should increase the limit in /etc/security/limits.conf for the user with whose account Tomcat is running and restart the process from a newly opened shell, check using /proc/<PID>/limits if the new limit is actually used, and see if Tomcat's behavior is improved.
While I don't have a direct answer to solve your problem, I'd like to offer my methods to find what's wrong.
Intuitively there are 3 assumptions:
If your clients hold their connections and never release, it is quite possible your server hits the max connection limit even there is no communications.
The non-responding state can also be reached via various ways such as bugs in the server-side code.
The hardware conditions should not be ignored.
To locate the cause of this problem, you'd better try to replay the scenario in a testing environment. Perform more comprehensive tests and record more detailed logs, including but not limited:
Unit tests, esp. logic blocks using transactions, threading and synchronizations.
Stress-oriented tests. Try to simulate all the user behaviors you can come up with and their combinations and test them in a massive batch mode. (ref)
More specified Logging. Trace client behaviors and analysis what happened exactly before the server stopped responding.
Replace a server machine and see if it will still happen.
The short answer:
Use the NIO connector instead of the default BIO connector
Set "maxConnections" to something suitable e.g. 10,000
Encourage users to use HTTPS so that intermediate proxy servers can't turn 100 page requests into 100 tcp connections.
Check for threads hanging due to deadlock problems, e.g. with a stack dump (kill -3)
(If applicable and if you're not already doing this, write your client app to use the one connection for multiple page requests).
The long answer:
We were using the BIO connector instead of NIO connector. The difference between the two is that BIO is "one thread per connection" and NIO is "one thread can service many connections". So increasing "maxConnections" was irrelevant if we didn't also increase "maxThreads", which we didn't, because we didn't understand the BIO/NIO difference.
To change it to NIO, put this in the element in server.xml:
protocol="org.apache.coyote.http11.Http11NioProtocol"
From what I've read, there's no benefit to using BIO so I don't know why it's the default. We were only using it because it was the default and we assumed the default settings were reasonable and we didn't want to become experts in tomcat tuning to the extent that we now have.
HOWEVER: Even after making this change, we had a similar occurrence: on the same day, HTTPS became unresponsive even while HTTP was working, and then a little later the opposite occurred. Which was a bit depressing. We checked in 'catalina.out' that in fact the NIO connector was being used, and it was. So we began a long period of analysing 'netstat' and wireshark. We noticed some periods of high spikes in the number of connections - in one case up to 900 connections when the baseline was around 70. These spikes occurred when we synchronised our databases between the main production server and the "appliances" we install at each customer site (schools). The more we did the synchronisation, the more we caused outages, which caused us to do even more synchronisations in a downward spiral.
What seems to be happening is that the NSW Education Department proxy server splits our database synchronisation traffic into multiple connections so that 1000 page requests become 1000 connections, and furthermore they are not closed properly until the TCP 4 minute timeout. The proxy server was only able to do this because we were using HTTP. The reason they do this is presumably load balancing - they thought by splitting the page requests across their 4 servers, they'd get better load balancing. When we switched to HTTPS, they are unable to do this and are forced to use just one connection. So that particular problem is eliminated - we no longer see a burst in the number of connections.
People have suggested increasing "maxThreads". In fact this would have improved things but this is not the 'proper' solution - we had the default of 200, but at any given time, hardly any of these were doing anything, in fact hardly any of these were even allocated to page requests.
I think you need to debug the application using Apache JMeter for number of connection and use Jconsole or Zabbix to look for heap space or thread dump for tomcat server.
Nio Connector of Apache tomcat can have maximum connections of 10000 but I don't think thats a good idea to provide that much connection to one instance of tomcat better way to do this is to run multiple instance of tomcat.
In my view best way for Production server: To Run Apache http server in front and point your tomcat instance to that http server using AJP connector.
Hope this helps.
Are you absolutely sure you're not hitting the maxThreads limit? Have you tried changing it?
These days browsers limit simultaneous connections to a max of 4 per hostname/ip, so if you have 50 simultaneous browsers, you could easily hit that limit. Although hopefully your webapp responds quickly enough to handle this. Long polling has become popular these days (until websockets are more prevalent), so you may have 200 long polls.
Another cause could be if you use HTTP[S] for app-to-app communication (that is, no browser involved). Sometimes app writers are sloppy and create new connections for performing multiple tasks in parallel, causing TCP and HTTP overhead. Double check that you are not getting an inflood of requests. Log files can usually help you on this, or you can use wireshark to count the number of HTTP requests or HTTP[S] connections. If possible, modify your API to handle multiple API calls in one HTTP request.
Related to the last one, if you have many HTTP/1.1 requests going across one connection, and intermediate proxy may be splitting them into multiple connections for load balancing purposes. Sounds crazy I know, but I've seen it happen.
Lastly, some crawl bots ignore the crawl delay set in robots.txt. Again, log files and/or wireshark can help you determine this.
Overall, run more experiments with more changes. maxThreads, https, etc. before jumping to conclusions with maxConnections.
I have written simple server in Qt, which responses for TCP requests with simple string (few bytes), the response and request are constant sets of data. I have compiled it on Raspberry Pi (Arch Linux), then ran and connected it to my LAN. On my laptop I ran Jmeter with TCP Sampler.
After 5 minutes responding to 15 threads server stays on constant 80ms time of response. Then, after 8 minutes it starts to falling down:
time - avg response time
5mins - 80ms
8mins - 72ms
10mins - 44ms
12mins and more - 20ms
And it stays on this about 20ms. Why is that happening? Is there some cache mechanism or just some random conditions changing? I cant run the tests again and I have no idea where is the possibility to cache the sending data.
How many hits per seconds are you getting?
The TCP sampler will NOT cache the results.
Maybe something in the OS is doing some caching?
The answer maybe too late, but I would like to share my experience in a similar situation when I was debugging a performance issue. Using a network sniffer to capture the packets, then look at a few sessions to check the response time. You can either prove or disprove the reported response time by traffic generator is correct or not and go from there. Good luck.