Azure Application Gateway HTTP Status 0 Responses

Context: You have a website running on Azure App Service that has a Azure Application Gateway in front.

Problem: Your clients receive the dreaded ERR_CONNECTION_CLOSED error randomly.

 

Troubleshooting: If you look at the Application Gateway logs, you will notice that the HttpStatus is 0. It is not a standard HTTP status code. You will also notice that SentBytes is also 0.

In such cases, the App Gateway does not forward the traffic to your backend target.

Cause: The predominant cause of such issues is that your application exceeded a certain Application Gateway limits as described in https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/azure-subscription-service-limits#azure-application-gateway-limits . For example, you may have cookie data that exceeds the 16 KB limit for HTTP/2. You can check your cookie sizes in Developer tools as shown below.

 

 

Unfortunately, as of August 2025, the only way to know what limit you exceeded is by opening at ticket with Microsoft Support.  

Solution: Modify your application code or adjust the appropriate configuration values, if applicable. 

blog@aileronconsulting.com
 

Azure Automated ML Batch Endpoint Spacy 3.7.4 compatibility issue

 If you tried to create a Batch Endpoint on Azure ML Studio and receive an error like the one shown below, the solution is provided in this blog post. If you need any assistance, feel free to reach out to blog@aileronconsulting.com.

=========================================================

#10 401.7 The conflict is caused by:
#10 401.7     The user requested spacy==3.7.4
#10 401.7     en-core-web-sm 3.4.1 depends on spacy<3.5.0 and >=3.4.0
#10 401.7 
#10 401.7 To fix this you could try to:
#10 401.7 1. loosen the range of package versions you've specified
#10 401.7 2. remove package versions to allow pip attempt to solve the dependency conflict
#10 401.7 
#10 401.7 
#10 401.7 failed
#10 401.7 
#10 401.7 CondaEnvException: Pip failed

=========================================================

The issue is in the environment file and the package en_core_web_sm-3.4.1 is not compatible with spacy 3.7.4.

Reach out (blog@aileronconsulting.com) if you would like to create custom environment that uses en_core_web_sm-3.7.1, which is compatible with the spacy package and use this base image  https://mcr.microsoft.com/azureml/curated/ai-ml-automl-dnn-gpu:21.

  

Azure Front Door with Wildcard domains

 When setting up Azure Front Door with wildcard domain names, there are a few things that need to be taken care of to get everything working correctly. Here are some key steps -

1. Add your domain.
   
2. Create the Origin Group / Origin. When creating the Origin leave the Origin Host Header blank. If you have a Private Link to, say, a backend load balancer, then enable that as well.
   
   
   
   
3. In your Front Door Endpoint, add the route to your wildcard domain.
   
   
   
   
4. Since you would need to create a CNAME to point to the endpoint, use HTTP Forwarding from your DNS server (or DNS provider) for your naked domain to, say, www.whateveryourdomainis.com. Then create a CNAME for www to point to the Endpoint.
   
   
   
   
   If you have any questions, please reach out to blog@aileronconsulting.com. We are happy to assist.

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Azure SQL Iaas Agent Not Updating Data on Azure Portal

 On Azure Portal you can install "SQL Virtual Machine" resource to monitor your Windows Virtual Machines to automate management and administration tasks. Sometimes Azure Portal does not reflect the state of your VM and there would be no data displayed on the Azure Portal for the SQL VM resource. Your first option is to Force repair as shown below.

 

If that doesn't work you can try to run the following command from Azure CLI. Note that you will get a warning about sql_management_mode being deprecated but you can ignore it.

az sql vm create --name YOURSQLVMNAM --resource-group YOURRESOURCEGROUPNAME --location YOURRESOURCELOCATION --license-type payg --sql-mgmt-type Full

 

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Adding an existing database to Azure Elastic Pool - 'System' is not a valid database edition in this version of SQL Server. Error

 When adding an existing database to an Azure Elastic Pool you may encounter the "'System' is not a valid database edition in this version of SQL Server." error message. To address this issue, go to the "Compute + Storage" setting for your database and modify it to a "Standard" Service tier at a minimum.

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