Azure Insights: Slow VNet calls; VM disk encryption; API connections; Service Bus dead lettering

December 6 2021

Azure pros discuss how to resolve slow calls with VMs, Service Bus dead lettering, VM disk encryption, and renaming API connections.

Resolving slow calls with VNets integrated with Azure Web App

Microsoft MVP Mike Stephenson discussed ways to troubleshoot performance issues with a web app on Azure App Service. He found the code worked and the API call was returning data, but noticed extended call duration issues. Checking an App Insights log, he found that calls to external dependencies were taking about seven seconds.

By running the code locally, he ruled out code issues, leading him to suspect DNS problems. Stephenson wrote:

I then remembered the old magic setting for WEBSITE_DNS_SERVER and ive never really explored what happens if this setting isnt added but it looked like what happened was that the outbound traffic from the web app is using the on prem DNS to attempt to resolve addresses and there was a latency overhead doing that on the first hit. We added the WEBSITE_DNS_SERVER setting and the resolution of the public dependencies immediately dropped right down and the call duration for that first call dropped from 57 secs overall to around 400ms. All of the calls out to external dependencies which were taking 7 secs dropped to 30ms or so.

VM disk encryption options

Harinder Kohli, writing on MyKloud, looked at ways to encrypt a VM disk. Platform-managed keys serve the purpose of encryption at rest, and in combination with customer-managed keys can achieve double encryption.

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