I maintain an azure cloud service. It is set to auto-scale based on load. To monitor the health of this service I have another service which pings this service every 2 minutes. The usual response time from this service is around 100ms.
Once or twice a week I see that the service does not respond. It is not really a worry for me - because it happens quite infrequently. I still am trying to figure out what could be causing the service to not respond. I do not think the problem is with the pinging service - I don't see any of the other services (not on azure, but on other servers) that it pings having any issues.
What could be causing these occasional delays. Any other azure service owners seeing such delays ?
Having quite similar problems. But I use Applications Inside, so I have some statistics. For example that reponse time increases together with SQL azure access time and CPU usage. My average response time according to Applications Inside is about 600ms and average RPS is about 0,6. During these problems RPS usually higher than avarage - up to 1.5, but average response time grows up to 1min! (During the day my RPS can grow up to 3 or even higher without any reponse time growth). As I have 1min sql connection timeout and I have drammatical growth of total SQL azure access time during this periods I can assume that problem happens bacause of SQL Azure. This also happens once a day or two, for about 10-15 minutes max and my ping service also always reports that service doesn't respond.
So my advice here - install Application Insights to analyze what happens dusring these response delays. It would be great if you share your results here.
P.S. I also use autoscale based on load. Though it doesn't really help in these concrete situations.
Related
We have a doubt about Azure because in some cases we have some dead times when we received requests in one of our AppServices or when a Service Bus triggers, for example, an Azure Functions.
If you see this image, you will see an example:
AppInsight Example Image
We execute a Request and at 5 seconds, but Azure delays more than 30 seconds to start the execution. We made a lot of optimizations in our apps, but we have no visibility about this delay.
Did someone face the same issue and found some solution? We believe it is a performance issue in the Workers, but, this happens also when the Workers are with a low load of memory and CPU. So we don't know how to scale horizontally automatically the resource if it is without load.
This happens also in our AZF, but we believe it's an issue between the Service Bus and the container of the AZF. In these cases we found the AZF has a higher consumption of CPU, but we don't why, because in the local environment we process a lot of messages with multithreading without any problem.
We have ASP.Net Core 2.1 Web API hosted in AppService (S1) that talks to Azure SQL DB (S1-20DTUs). Both are in same region. During load testing we found that some API instances are taking too much time to return the result.
We tried to troubleshoot the performance issue and below are our observations.
API responds within 0.5 secs most of the time.
API methods are all async methods.
Sometimes it takes around 50 secs to over a minute.
CPU & Memory utilization are below 60%
Database has 20 DTU capacity, out of which 6 DTUs are used during load testing.
In the below example snapshot from Application Insights, we see total duration of the request was 27.4 secs. But the database dependency duration was just 97ms. There is no activity till the database was called. Please refer below example.
Can someone please help me to understand what was happening in this 27 secs of wait time. What could be the reason for this?
I would recommend checking the Application Map on Application Insights resource as shown below to double check the dependencies.
Verify the CPU and Memory metrics by going to the "Diagnose and solve problems" link on App service as shown below and run the Availability and Performance report to find out if there were any issues during your load testing.
Use Async methods on your API to maximize the CPU usage. It may be that the worker process threads are hitting the limits and your app is the bottleneck. You should get some insights when you run the report mentioned in point 2 above.
The S1 tier will support no more than 900 concurrent session. If you request per second (RPS rate) during the load test is very high you may face issues.
Also S3 and above are recommended for intensive workloads. Checking if all the connections are closed properly also helps
You can find details about different pricing tiers and their capabilities in the below link
https://learn.microsoft.com/en-us/azure/sql-database/sql-database-dtu-resource-limits-single-databases
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.
Whenever I start my Azure Functions app, Live Metrics Streaming in Application Insights shows that there are a high number of servers online -- currently sitting at 24 and climbing -- and seems to bring another server online every few seconds or so. This is before I even make a call to any HttpTriggers. And for every call I make to an HttpTrigger, Functions seems to bring another server online (at least that's what Application Insights is saying).
I'm at a complete loss of how to account for this behavior, especially since my app isn't doing anything yet (no requests). There aren't any logged errors that I can see except for the "Unable to acquire Singleton lock" one for new servers, which I'd expect. The CPU% for a server spikes when it comes online, but then goes back down to 0% within a few seconds and stays there.
Even more bizarre is that when I left the app running over night, I saw 180 servers online in the morning and calls to my API were very slow.
Is the "servers online" metric in Live Metrics Stream misleading with Azure Functions, or is there any way to find out why there are so many servers being brought online? Does anyone have any other suggestions for how to figure out what's happening?
We run a web service that gets 6k+ requests per minute during peak hours and about 3k requests per minute during off hours. Lots of data feeds compiled from 3rd party web services and custom generated images. Our service and code is mature, we've been running this for years. A lot of work by good developers has gone into our service's code base.
We're migrating to Azure, and we're seeing some serious problems. For one, we are seeing our Premium P1 SQL Azure database routinely become unavailable for 1-2 full entire minutes. I'm sorry, but this seems absurd. How are we supposed to run a web service with requests waiting 2 minutes for access to our database? This is occurring several times a day. It occurs less after switching from Standard level to Premium level, but we're nowhere near our DB's DTU capacity and we're getting throttled hard far too often.
Our SQL Azure DB is Premium P1 and our load according to the new Azure portal is usually under 20% with a couple spikes each hour reaching 50-75%. Of course, we can't even trust Azure's portal metrics. The old portal gives us no data for our SQL, and the new portal is very obviously wrong at times (our DB was not down for 1/2 an hour, like the graph suggests, but it was down for more than 2 full minutes):
Azure reports the size of our DB at a little over 12GB (in our own SQL Server installation, the DB is under 1GB - that's another of many questions, why is it reported as 12GB on Azure?). We've done plenty of tuning over the years and have good indices.
Our service runs on two D4 cloud service instances. Our DB libraries are all implementing retry logic, waiting 2, 4, 8, 16, 32, and then 48 seconds before failing completely. Controllers are all async, most of our various external service calls are async. DB access is still largely synchronous but our heaviest queries are async. We heavily utilize in-memory and Redis caching. The most frequent use of our DB is 1-3 records inserted for each request (those tables are queried only once every 10 minutes to check error levels).
Aside from batching up those request logging inserts, there's really not much more give in our application's db access code. We're nowhere near our DTU allocation on this database, and the server our DB is on has like 2000 DTU's available to be allocated still. If we have to live with 1+ minute periods of unavailability every day, we're going to abandon Azure.
Is this the best we get?
Querying stats in the database seems to show we are nowhere near our resource limits. Also, on premium tier we should be guaranteed our DTU level second-by-second. But, again, we go more than an entire solid minute without being able to get a database connection. What is going on?
I can also say that after we experience one of these longer delays, our stats seem to reset. The above image was a couple minutes before a 1 min+ delay and this is a couple minutes after:
We have been in contact with Azure's technical staff and they confirm this is a bug in their platform that is causing our database to go through failover multiple times a day. They stated they will be deploying fixes starting this week and continuing over the next month.
Frankly, we're having trouble understanding how anyone can reliably run a web service on Azure. Our pool of Websites randomly goes down for a few minutes a few times a month, taking our public sites down. If our cloud service returns too many 500 responses something in front of it is cutting off all traffic and returning 502's (totally undocumented behavior as far as we can tell). SQL Azure has very limited performance and obviously isn't ready for prime time.