Azure Application Insights warned me of failed dependent requests on my site

August 15, 2018 Comment on this post [7] Posted in Azure

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I've been loving Application Insights ever since I hooked it up to my Podcast Site. Application Insights is stupid cheap and provides an unreal number of insights into what's going on in your site. I hooked it up and now I have a nice dashboard showing what's up. It's pretty healthy.

Here's an interesting view that shows the Availability Test that's checking my site as well as outbound calls (there isn't a lot as I cache aggressively) to SimpleCast where I host my shows.

Availability is important, of course, so I set up some tests from a number of locations. I don't want the site to be down in Brazil but up in France, for example.

However, I got an email a week ago that said my site had a sudden rise in failures. Here's the thing, though. When I set up a web test I naively thought I was setting up a "ping." You know, a knock on the door. I figured if the WHOLE SITE was down, they'd tell me.

Here's my availability for today, along with timing from a bunch of locations world wide.

Check out this email. The site is fine; that is, the primary requests didn't fail. But dependent request did fail! Application Insights noticed that an image referenced on the home page was suddenly a 404! Why suddenly? Because I put the wrong date and time for an episode and it auto-published before I had the guest's headshot!

I wouldn't have noticed this missing image until a user emailed me, so I was impressed that Application Insights gave me the heads up.

1 dependant request failed

Here is the chart for that afternoon when I published a bad show. Note that the site is technically up (it was) but a dependent request (a request after the main GET) failed.

This is a client side failure, right? An image didn't load and it notified me. Cool. I can (and do) also instrument the back end code. Here you can see someone keeps sending me a PUT request, perhaps trying to poke at my site. By the way, random PUT person has been doing this for months.

I can also see slowest requests and dig as deep as I want. In fact I did a whole video on digging into Azure Application Insights that's up on YouTube.

I've been using Application Insights for maybe a year or two now. Its depth continues to astound me. I KNOW I'm not using it to its fullest and I love that I'm still surprised by it.

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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Comment on this post [7]

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August 15, 2018 20:14

AppInsights is great, I just wish it was available in more regions! There were only 6 or 7 regions available last time I checked, and not the one I'm using :(

Marc Roussy

August 15, 2018 20:17

@Lucas so your web site has links to images that suppose to return 404? In this case you can un-check the check box that validates all page resources when creating a web test.

If you are talking about different feature - server requests returning 404 - you have options:

Filter those in UI or Analytics. In Failures blade - there is a button for it

Implement telemetry initializer to mark them as successful or telemetry processor to completely ignore http://apmtips.com/blog/2016/12/03/request-success-and-response-code/

Sergey Kanzhelev

August 16, 2018 7:08

@Sergey, they're server requests returning a 404 for files not on my server (not a missing a missing file, just an incorrect request).

I had setup an azure alert to email me if more than 5 server 404 requests occur in the span of 2 minutes, since as a .NET Core app a 404 error could mean a real error in our code, but too many false positives from external incorrect requests that I can't filter out.

I've removed the alert, I'll just look at Azure portal from time to time to review until I find a better option.

I do like the automated response degradation emails, it helps to pin points areas that need improvement.

Lucas

August 16, 2018 18:50

@Lucas one option for you to investigate is to set a data-based alert like this: https://docs.microsoft.com/azure/log-analytics/log-analytics-tutorial-response. Perhaps you can check the url of failed requests and only alert for requests from your domain.

Sergey Kanzhelev

August 18, 2018 15:07

Amazing post Scott,
My favourite Azure Application,

Kevin

Kevin

August 20, 2018 21:29

Hello Scott, I am facing a carzy issue since I added an application insights to our site. Everytime we publish some change even a single file like .aspx, it slows down first request to every resource of site. I guess it might be deleting the compiled version of pages, which generates on runtime. But why it deletes every page's compiled version when I am updating only one file of site? Also why it does same thing on code behind dlls update, if they are already compiled?

I added application insights as a plugin instrumented directly from Azure portal. And my application is a asp.net webform application.

Please share your thoughts to resolve this issue.

Shrikant N

August 27, 2018 18:10

Now, if only API responses would use 400-style errors when they actually have a problem; we'd probably see just how inconsistent they may be. Sick of a 200 response with the body of

{"success": "failure"}

Shawn

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