I have an api application that is running in a docker container, and since moving to AWS, the api stops daily with the error: Erlang closed the connection. I've monitored the server during that time and no IOPS seem to be causing this issue. Beyond that though, when the api fails, it won't restart on it's own on one of our clusters. I'm not sure where to find the logs to get more context and could use any input that may be helpful. Also, more context here, is that this api worked fairly well before in our data-center/physical server space, but now in AWS, it fails daily. Any thoughts or suggestions as to why this may be failing to restart?
I've looked at the syslogs and the application server logs and don't see any kind of failures. Maybe I'm not looking in the proper place. At this point, someone from one of our teams has to manually restart the api with an init.d command. I don't want to create a cron job to "fix" this because that's a band-aid and not a true fix.
There really isn't enough information on the structure of your app or its connections, so no one can give a "true fix".
The problem may be as small as configuring your nodes differently, changing some of the server's local configurations, or you may need some "keep alive" handler towards AWS.
Maybe try adding a manual periodic dump to see if its an accumulating problem, but I believe if Erlang closed the connection there's a problem between your API and AWS, and your API can't understand where it is located.
Related
We are using Azure DevOps Self hosted agents to build and release our application. Often we are seeing
below error and recovering automatically. Does anyone know what is this error ,how to tackle this and where to exactly check logs about the error ?
We stopped hearing from agent <agent name>. Verify the agent machine is running and has a healthy network connection. Anything that terminates an agent process, starves it for CPU, or blocks its network access can cause this error. For more information, see: https://go.microsoft.com/fwlink?Linkid=846610
This seems to be a known issue with both self-hosted and Microsoft-hosted agents that many people have been reporting.
Quoting the reply from #zachariahcox from the Azure Pipelines Product Group:
To provide some context, the azure pipelines agent is composed of two
processes: agent.listener and agent.worker (one of these per
step in the job). The listener is responsible for reporting that
workers are still making progress. If the agent.listener is unable
to communicate with the server for 10 minutes (we attempt to
communicate every minute), we assume something has Gone Wrong and
abandon the job.
So, if you're running a private machine, anything that can interfere
with the listener's ability to communicate with our server is going to
be a problem.
Among the issues i've seen are anti-virus programs identifying it as a
threat, local proxies acting up in various ways, the physical machine
running out of memory or disk space (quite common), the machine
rebooting unexpectedly, someone ctrl+c'ing the whole listener process,
the work payload being run at a way higher priority than the listener
(thus "starving" the listener out), unit tests shutting down network
adapters (quite common), having too many agents at normal priority on
the same machine so they starve each other out, etc.
If you think you're seeing an issue that cannot be explained by any of
the above (and nothing jumps out at you from the _diag logs folder),
please file an issue at
https://azure.microsoft.com/en-us/support/devops/
If everything seems to be perfectly alright with your agent and none of the steps mentioned in the Pipeline troubleshooting guide help, please report it on Developer Community where the Azure DevOps Team and DevOps community are actively answering questions.
We have a long running ASP.NET WebApp in Azure which has no real endpoints exposed – it serves a single functional purpose primarily reading and manipulating database data, effectively a batched, scheduled task, triggered by a timer every 30 seconds.
The app runs fine most of the time but we are seeing occasional issues where the CPU load for the app goes close to the maximum for the AppServicePlan, instantaneously rather than gradually, and stops executing any more timer triggers and we cannot find anything explicitly in the executing code to account for it (no signs of deadlocks etc. and all code paths have try/catch so there should be no unhandled exceptions). More often than not we see errors getting a connection to a database but it’s not clear if those are cause or symptoms.
Note, this is the only resource within the AppService Plan. The Azure SQL database is in the same region and whilst utilised by other apps is very lightly used by them and they also exhibit none of the issues seen by the problem app.
It feels like this is infrastructure related but we have been unable to find anything to explain what is happening so if anyone has any suggestions for where we should be looking they would be gratefully received. We have enabled basic Application Insights (not SDK) but other than seeing CPU load spike prior to loss of app response there is little information of interest given our limited knowledge of how to best utilise Insights.
According to your description, I thought of two points to troubleshoot your problem. First of all, you can track the running status of your program through the code, and put a log at the beginning and end of your batch scheduled tasks to record the status of each run. If possible, record request and response information and start and end information. This can completely record the time and running status of your task.
Secondly, you can record logs before the program starts database operations, and whether the database connection is successful. The best case is to be able to record, what business will trigger CPU load when operating, and track the specific operating conditions, in order to specifically analyze what causes the database connection failure.
Because you cannot reproduce your problem, you can only guess the cause of the problem. If you still can't find where the problem is through the above two points, then modify your timer appropriately, and let the program trigger once every 5 minutes instead of 30s.
I am doing small project of application that will monitor some servers.
It will base on telnet port check, ping, and also it will use libraries to connect directly to databases (MSSQL, Oracle, MySQL) to check their status.
I wonder what will be the best effective solution for this idea, currently with around 30 servers it works quite smooth, around 2.5sec to check status for all of them (running async). However I am worried that in the future with more servers it might get worse. Hence thinking about using some alternative like Worker Threads maybe? or some multi processing? Any ideas? Everything is happening in internal network so I do not expect huge latency.
Thank you in advance.
Have you ever tried the PM2 cluster mode:
https://pm2.keymetrics.io/docs/usage/cluster-mode/
The telnet stuff is TCP, which Node.js does very well using OS-level networking events. The connections to databases can vary. In the case of Oracle, you'll likely be using the node-oracledb. Those are SQL*Net connections that rely on the OCI libs and Node.js' thread pool. The thread pool defaults to four threads, but you can grow it up to 128 per Node.js process. See this doc for info:
https://oracle.github.io/node-oracledb/doc/api.html#-143-connections-threads-and-parallelism
Having said all that, other than increasing the size of the thread pool, I wouldn't recommend you make any changes. Why fight fires before they're burning? No need to over-engineer things. You're getting acceptable performance given the current number of servers you have.
How many servers do you plan to add in, say, 5 years? What's the difference in timing if you run the status checks for half of the servers vs all of them? Perhaps you could use that kind of data to make an educated guess as to where things would go.
As you add new ones, keep track of the total time to check the status. Is it slipping? If so, look into where the time is being spent and write the solution that will help.
This is kind of a multi-tiered question in which my end goal is to establish the best way to setup my server which will be hosting a website as well as a service (using Socket.io) for an iOS (and eventually an Android) app. Both the app service and the website are going to be written in node.js as I need high concurrency and scaling for the app server and I figured whilst I'm at it may as well do the website in node because it wouldn't be that much different in terms of performance than something different like Apache (from my understanding).
Also the website has a lower priority than the app service, the app service should receive significantly higher traffic than the website (but in the long run this may change). Money isn't my greatest priority here, but it is a limiting factor, I feel that having a service that has 99.9% uptime (as 100% uptime appears to be virtually impossible in the long run) is more important than saving money at the compromise of having more down time.
Firstly I understand that having one node process per cpu core is the best way to fully utilise a multi-core cpu. I now understand after researching that running more than one per core is inefficient due to the fact that the cpu has to do context switching between the multiple processes. How come then whenever I see code posted on how to use the in-built cluster module in node.js, the master worker creates a number of workers equal to the number of cores because that would mean you would have 9 processes on an 8 core machine (1 master process and 8 worker processes)? Is this because the master process usually is there just to restart worker processes if they crash or end and therefore does so little it doesnt matter that it shares a cpu core with another node process?
If this is the case then, I am planning to have the workers handle providing the app service and have the master worker handle the workers but also host a webpage which would provide statistical information on the server's state and all other relevant information (like number of clients connected, worker restart count, error logs etc). Is this a bad idea? Would it be better to have this webpage running on a separate worker and just leave the master worker to handle the workers?
So overall I wanted to have the following elements; a service to handle the request from the app (my main point of traffic), a website (fairly simple, a couple of pages and a registration form), an SQL database to store user information, a webpage (probably locally hosted on the server machine) which only I can access that hosts information about the server (users connected, worker restarts, server logs, other useful information etc) and apparently nginx would be a good idea where I'm handling multiple node processes accepting connection from the app. After doing research I've also found that it would probably be best to host on a VPS initially. I was thinking at first when the amount of traffic the app service would be receiving will most likely be fairly low, I could run all of those elements on one VPS. Or would it be best to have them running on seperate VPS's except for the website and the server status webpage which I could run on the same one? I guess this way if there is a hardware failure and something goes down, not everything does and I could run 2 instances of the app service on 2 different VPS's so if one goes down the other one is still functioning. Would this just be overkill? I doubt for a while I would need multiple app service instances to support the traffic load but it would help reduce the apparent down time for users.
Maybe this all depends on what I value more and have the time to do? A more complex server setup that costs more and maybe a little unnecessary but guarantees a consistent and reliable service, or a cheaper and simpler setup that may succumb to downtime due to coding errors and server hardware issues.
Also it's worth noting I've never had any real experience with production level servers so in some ways I've jumped in the deep end a little with this. I feel like I've come a long way in the past half a year and feel like I'm getting a fairly good grasp on what I need to do, I could just do with some advice from someone with experience that has an idea with what roadblocks I may come across along the way and whether I'm causing myself unnecessary problems with this kind of setup.
Any advice is greatly appreciated, thanks for taking the time to read my question.
I have a classic ASP application that has been stable for years and now we're having all kinds of problems with it. After moving the app between machines and wiping the original so we could have a fresh install of windows, we've come to the following "symptom". The app pools do not appear to allow for multiple simultaneous requests. Here's what we are seeing:
The app runs normally for most people, but when someone within one of the app pools accesses a long-running script (usually one with lots of DB access) all of the other users in the pool must wait for that script to complete. Once the script completes, everyone else's requests run. This initially made us suspect the DB connection string or something.
UNTIL... we noticed also that large file uploads into our system also cause the app pool to stop responding. What's interesting about this is that we're using the SAFileup COM+ object to do our uploads, which has a progress display in a pop-up window. When you go to upload the file, the progress display comes up, but then never refreshes to show upload progress. If you wait it out, however, the file will eventually upload and the other pending requests will process as normal.
Our app pools are in the default configuration, using the IWAM account to launch. I checked to ensure that the IWAM account has all the appropriate permissions. It does.
We've tried a variety of DB connection strings, none solved the problem (though I'm thinking it's not the DB connection string). Just in case someone thinks it is, here's our connection string: "Provider=SQLNCLI;Trusted_Connection=yes;Server=(local);Database=demo;". It couldn't be simpler. This string was previously not a problem.
I fussed with the web gardens thing and it does, indeed, make the system respond to multiple requests, but each worker thread in the garden has its own session state which causes our users to get booted when their request gets randomly assigned to a new worker thread. Only having a single worker process in the garden was never an issue before anyway.
I've used SQL Profiler and sp_who2 to see if during the long-running scripts there are any deadlocks or blocks on the SQL Server. There are not.
The issues initially started after we had installed some patches from Microsoft. We wiped a machine clean and installed Win2k3 server, then SP2, and then didn't patch anymore after that. The problem remained, so it doesn't appear to have been a patch.
I'm pretty much at a loss now... does anyone have any experience with similar issues? If so, how were they fixed?
Check that you don't have ASP debugging enabled on the server. This will force the ASP script engine to run on a single thread.
Sounds like an limit on the number of concurrent incoming requests to the IIS or the Windows Server..
Check out http://blogs.msdn.com/b/david.wang/archive/2006/04/12/howto-maximize-the-number-of-concurrent-connections-to-iis6.aspx and http://forums.iis.net/p/1152112/1880908.aspx#1880908 on how to tweak the settings.