We are running a setup on Azure consisting:
S3 web app in UK South
S2 failover in UK West
200DTU Elastic Pool with around 25 databases
Redis server
Several times this week, we have had periods where Redis has stopped hitting and missing data, and no additional items are being added to the cache. In effect the caching completely ceases being available.
Flushing the cache does not make any difference to the issue - nothing is added, nothing is hit or even missed.
The only way to re-enable is to restart the web app itself. After which everything is back to normal.
Our developers are looking into potential causes in our codebase, but I wonder if anyone has any ideas on how to diagnose or solve this issue.
Thanks
If restarting your web app fixes it, it sounds like some contention on the client side. You might find this (https://gist.github.com/JonCole/db0e90bedeb3fc4823c2#file-diagnoserediserrors-clientside-md) link useful. It could likely be threadpool or CPU contention on the client machines hosting your web app.
Related
since a month one of our web application hosted as WebApp on Azure is having some kind of problem and I cannot find the root cause of that.
This WebApp is hosted on Azure on a 2 x B2 App Service Plan. On the same App Service Plan there is another WebApp that is currently working without any issue.
This WebApp is an ASP.NET WebApi application and exposes a REST set of API.
Effect: without any apparent sense (at least for what I know by now), the ThreadCount metric starts to spin up, sometimes very slowly, sometimes in few minutes. What happens is that no requests seems to be served and the service is dead.
Solution: a simple restart of the application (an this means a restart of the AppPool) causes an immediate obvious drop of the ThreadCount and everything starts as usual.
Other observations: there is no "periodicity" in this event. It happened in the evening, in the morning and in the afternoon. It seems that evening is a preferred timeframe, but I won't say there is any correlation.
What I measured through Azure Monitoring Metric:
- Request Count seems to oscillate normally. There is no peak that causes that increase in ThreadCount
- CPU and Memory seems to be normal, nothing strange.
- Response time, like the others metrics
- Connections (that should be related to sockets) oscillates normally. So I'd exclude something related to DB connections.
What may I do in order to understand what's going on?
After a lot of research, this happened to be related to a wrong usage of Dependency Injection (using Ninject) and an application that wasn't designed to use it.
In order to diagnose, I discovered a very helpful feature in Azure. You can reach it by entering into the app that is having the problem, click on "Diagnose and solve problems" then click on "Diagnostic tools" and then select "Collect .NET profiler report". In that panel, after configuring the storage for the diagnostic files, you can select "Add thread report".
In those report you can easily understand what's going wrong.
Hope this helps.
We have few of our internal business services hosted on an isolated ASE in Azure.
These services run on a medium app service plan with 2 instances.
This environment has been in production and use for little more than a month now and has been performing fairly well apart from the occasional sudden CPU spike to 100% in one of the instance which bring down the services.
We don't have auto scaling setup but have 2 instances running all the time.
The services are `aspnetcore` webapi and the runtime is dotnet core 2.0.
Every time I have come across this issue in the last couple of weeks I have not been lucky enough to login to kudu and get a process dump to investigate further. The business are literally behind my back to get the service up and running as quick as possible and the easiest route is to restart one of the faulting service or swap slots with a pre-prod environment.
Access to the ASE are also restricted from our network and makes it all the more difficult for me to switch to a WiFi and then go through jump boxes to login to kudu, I had asked our Ops engineer to get me the dump when this issue is reported but he has not been listening to me either, mostly for the same reasons as me not able to do it myself.
All exceptions I can see in Application Insights are due to the service themselves going down and there are no exceptions there which can cause the issue in the first place(at least I've not found it yet)
This lead me to take few guess and look for metrics, the only thing raising my
suspicions is garbage collection. I don't see any sudden spike in GC graphs as well, each time the service is re started the graph is fairly a straight line(24 hours) but increases day by day and ends up like below.
But the working memory is a sinusoid graph letting me think there are no memory leaks. But is the above graph over 3 days normal?
The drop is when I restart the service. But all services have a similar trajectory even the one that has not gone down.
I am not sure if this is a problem with an individual service or an environment configuration I have overlooked.
The API endpoints are simple CRUD operations and publish events to a service bus topic after each operation. There is a static `HttpClient` instance used to fetch data from another service. Apart from that there are no unmanaged resources and the DB connections are always wrapped in `using` statements.
I understand I would need a process dump to investigate further but my biggest concern is why is the application gateway(load balancer) not sending traffic to the healthy instance. Because of the gateway going unhealthy cloudflare returns a `502` response to clients using the api.
MS support haven't been able to help and have not answered if we have our load balancers working correctly.
The average number of requests is about 50-60 per minute.
CPU runs at less than 10% apart this sudden surge.
Thanks
It could be that the backend is pegged at 100% CPU and is unable to respond to Application Gateway health probes. When such an issue occurs, were you able to verify, using Backend health logs, the health state of your backends? If both backend instances were unhealthy, it would explain the 502s. If one of them was healthy and responding to probes, then new requests sent to Application Gateway would indeed flow to the healthy instance. If you suspect that is not the case then please reply back with subscription id, gateway name and approximate time window of incident for us to take a look.
We're experiencing CPU spikes on our Azure App Service Plan for no obvious reason. Its not something that stops the service, but we'd like to have an understanding of when&how that kind of things happen.
For example, CPU percentage sits at 0-1% range for days but then all of the sudden it spikes to 98%, 45%, 60% and comes back to 0-1% range very quickly. Memory stays unchanged at comfortable 40-45% level, no incoming requests to it, no web jobs, nothing unusual in logs, no failures, service health ok, nothing we could point our finger to as a reason.
We tried to find out through kudu > support > analyze (metrics)...but we couldn't get request submited. It just keeps giving error to try later.
There is only one web app running in that app service plan, its a asp.net core 2.0. web api.
Could someone shed some light on this kind of behavior? Is this normal, expected? If so, why it happens? Is there a danger that it spikes to 90% and don't immediately come back?
Just, what's going on?
After speaking with MS support i've got an answer it is a normal behavior coming from their monitoring tool:
We reviewed our internal tools taking as starting point 12/26 and
today 12/29 and we could notice that this was majority System
processes doing background tasks, which is normal for each sandbox
environment. In your case, it was mostly MonAgentCore.exe fluctuating
in CPU which is our diagnostic log capturing process and this looks
like a very temporary spike and appears normal.
We have an azure app service (running Umbraco), and once a day the system stops accepting requests. We know this because we have added logging to Application_BeginRequest, and during the 10-15 minute outage, no requests are logged. We also log the Application_EndRequest and keep a running counter of "active" requests, as we thought it may have been related to traffic volume, however the outage still occurs even when there are 0 active requests. The outage corrects itself after about 15 minutes with no interference. Restarting the app service "corrects" the outage quicker. There is nothing in the Umbraco logs (errors or otherwise) that would suggest anything is running. Upgrading Umbraco to the latest version (twice) has not resolved the issue. We have several other similarly sized and trafficked Umbraco sites that do not have this issue.
During the outage:
CPU stays steady at 5-20% usage
Memory stays steady at 30% usage
DTU (on azure sql db) stays steady at 10-20%
This tells me that none of the above are the bottlenecks, so I would guess there is some sort of deadlock or I/O issue. This leads to the question: from an infrastructure standpoint, knowing the above, what are some possible causes for the aforementioned behavior?
By looking at my Pingdom reports I have noted that my WebSite instance is getting recycled. Basically Pingdom is used to keep my site warm. When I look deeper into the Azure Logs ie /LogFiles/kudu/trace I notice a number of small xml files with "shutdown" or "startup" suffixes ie:
2015-07-29T20-05-05_abc123_002_Shutdown_0s.xml
While I suspect this might be to do with MS patching VMs, I am not sure. My application is not showing any raised exceptions, hence my suspicions that it is happening at the OS level. Is there a way to find out why my Instance is being shutdown?
I also admit I am using a one S2 instance scalable to three dependent on CPU usage. We may have to review this to use a 2-3 setup. Obviously this doubles the costs.
EDIT
I have looked at my Operation Logs and all I see is "UpdateWebsite" with status of "succeeded", however nothing for the times I saw the above files for. So it seems that the "instance" is being shutdown, but the event is not appearing in the "Operation Log". Why would this be? Had about 5 yesterday, yet the last "Operation Log" entry was 29/7.
An example of one of yesterday's shutdown xml file:
2015-08-05T13-26-18_abc123_002_Shutdown_1s.xml
You should see entries regarding backend maintenance in operation logs like this:
As for keeping your site alive, standard plans allows you to use the "Always On" feature which pretty much do what pingdom is doing to keep your website warm. Just enable it by using the configure tab of portal.
Configure web apps in Azure App Service
https://azure.microsoft.com/en-us/documentation/articles/web-sites-configure/
Every site on Azure runs 2 applications. 1 is yours and the other is the scm endpoint (a.k.a Kudu) these "shutdown" traces are for the kudu app, not for your site.
If you want similar traces for your site, you'll have to implement them yourself just like kudu does. If you don't have Always On enabled, Kudu get's shutdown after an hour of inactivity (as far as I remember).
Aside from that, like you mentioned Azure will shutdown your app during machine upgrade, though I don't think these shutdowns result in operational log events.
Are you seeing any side-effects? is this causing downtime?
When upgrades to the service are going on, your site might get moved to a different machine. We bring the site up on a new machine before shutting it down on the old one and letting connections drain, however this should not result in any perceivable downtime.