How do you use a Cosmos connection string in Azure App Service?

Question

How do you use a Cosmos connection string in Azure App Service?

JasonStone-1737 51

Hello,

I'm hoping someone can provide guidance on how to use a Cosmos DB connection string in Azure App Service Environment Variables.

I have placed a connection string in Azure App Service - Environment Variables - Connection Strings.

A log stream from Azure App Service indicates that a call to instantiate a CosmosClient from the Microsoft.Azure.Cosmos SDK with an ASP.NET Core app has received a null value.

This implies the Environment Variable from App Service is not passing any value.

One thing that puzzles me about the Environment Variable - Connection String setup in App Service is that you are to specify a "type" for a connection string and there is no explicit type listed as "Cosmos DB". The closest is "DocumentDB".

Does anyone know how to use a Cosmos DB connection string in Azure App Service Environment Variables?

Vahid Ghafarpour 23,385 Reputation points Volunteer Moderator

2024-03-06T03:21:47.2766667+00:00

May this guide helps you:

https://learn.microsoft.com/en-us/azure/static-web-apps/database-azure-cosmos-db?tabs=bash

** Please don't forget to close up the thread here by upvoting and accept it as an answer if it is helpful **
JasonStone-1737 51 Reputation points

2024-03-06T04:21:34.8933333+00:00

Thank you for your response. However, the documentation you provide is in the context of the Data API builder for REST and GraphQL Endpoints in the context of a static web application.

I'm asking about configuring a Cosmos DB connection string as an App Service Environment Variable.
ajkuma 28,036 Reputation points Microsoft Employee Moderator

2024-03-06T13:12:24.3433333+00:00

@JasonStone-1737 , Just to confirm, if you haven't tried you could set these as app settings instead of under the connection string section, kindly try this: View the Azure Cosmos DB keys in application settings

Also, to clarify, it's not really App Service Environment - Variables, there are "App Service - Environment Variables" - so just to clarify my understanding, are you leveraging ASE or App Service?

Connecting string is stored fine, on our test.

Please confirm/validate from here and check whether their string is properly populating
https://yourwebappnamehere.scm.azurewebsites.net/Env.cshtml

For additional details, I have reached out to you privately.
JasonStone-1737 51 Reputation points

2024-03-07T00:38:32.2333333+00:00

For clarification: The context of this question is Azure App Service (not App Service Environment), ASP.NET Core, and setting connection strings for Cosmos DB as an environment variable.

Here is one solution to the issue I have asked about: As “ajkuma” mentions, place the connection string as an “App Setting” environment variable. You can then use IConfiguration.GetSection() to retrieve it. If you start with using Azure Service Connector to setup your connection, Azure Service Connector will place the connection string in “App Setting”.

In case it might be helpful to someone, here is more information about the question of how to handle a connection string for Cosmos DB as an environment variable. I spent some time trying to find documentation on a Cosmos DB connection string as an Azure App Service environment variable and didn’t come up with anything to address the problem described below:

If you choose a connection string approach for a Cosmos DB connection for an ASP.NET Core application and have the connection string stored as an environment variable in Azure App Service - you may need to place the connection string as an “App Setting” variable and NOT as a “Connection String” variable.

I have not done extensive testing. However, a Cosmos DB connection string does not seem to work with ASP.NET Core app configuration using an Azure App Service ”Connection String” configuration for either “Document DB” or “Custom” string types.

After placing a Cosmos DB connection string as an Azure App Service “Connection String” variable as either type “Custom” or “DocumentDB”, I tried retrieving the environment variable both through a .NET IConfiguration.GetSection() call and an IConfiguration.GetConnectionString() call. I also tried playing with the prefix for a custom connection string documented at Configure apps - Azure App Service | Microsoft Learn. For example, I tried an IConfiguration.GetSection() call to a connection string of type “Custom” both without and with the “CUSTOMCONNSTR_” prefix. In all cases, a null value is returned for the attempt to retrieve the environment variable from App Service.

App Service is creating the environment variable and I haven’t updated the app to the latest .NET Core version yet - perhaps there is a problem in the .NET configuration code.
ajkuma 28,036 Reputation points Microsoft Employee Moderator

2024-03-08T04:52:23.9333333+00:00

Glad the approach of placing the connection string as an 'App Setting' environment variable works for you.
Connection string prefixes should also work, kindly see this doc section :Connection string prefixes, as you mentioned, updating the code to the latest .NET Core version would be helpful.

I'll summarize and convert the answer, request you to accept it as an answer - it will benefit users with a similar ask.
David Zeidman 0 Reputation points

2025-05-19T13:39:09.69+00:00

I was also looking to put my Cosmos DB connection string in the connection strings area. It seems really strange that there is no type option for Cosmos DB but there is for very many other kinds of connection strings

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Vahid Ghafarpour 23,385 Reputation points Volunteer Moderator

2024-03-06T03:21:47.2766667+00:00

May this guide helps you:

https://learn.microsoft.com/en-us/azure/static-web-apps/database-azure-cosmos-db?tabs=bash

** Please don't forget to close up the thread here by upvoting and accept it as an answer if it is helpful **
JasonStone-1737 51 Reputation points

2024-03-06T04:21:34.8933333+00:00

Thank you for your response. However, the documentation you provide is in the context of the Data API builder for REST and GraphQL Endpoints in the context of a static web application.

I'm asking about configuring a Cosmos DB connection string as an App Service Environment Variable.
ajkuma 28,036 Reputation points Microsoft Employee Moderator

2024-03-06T13:12:24.3433333+00:00

@JasonStone-1737 , Just to confirm, if you haven't tried you could set these as app settings instead of under the connection string section, kindly try this: View the Azure Cosmos DB keys in application settings

Also, to clarify, it's not really App Service Environment - Variables, there are "App Service - Environment Variables" - so just to clarify my understanding, are you leveraging ASE or App Service?

Connecting string is stored fine, on our test.

Please confirm/validate from here and check whether their string is properly populating
https://yourwebappnamehere.scm.azurewebsites.net/Env.cshtml

For additional details, I have reached out to you privately.
ajkuma 28,036 Reputation points Microsoft Employee Moderator

2024-03-08T04:52:23.9333333+00:00

Glad the approach of placing the connection string as an 'App Setting' environment variable works for you.
Connection string prefixes should also work, kindly see this doc section :Connection string prefixes, as you mentioned, updating the code to the latest .NET Core version would be helpful.

I'll summarize and convert the answer, request you to accept it as an answer - it will benefit users with a similar ask.
David Zeidman 0 Reputation points

2025-05-19T13:39:09.69+00:00

I was also looking to put my Cosmos DB connection string in the connection strings area. It seems really strange that there is no type option for Cosmos DB but there is for very many other kinds of connection strings

Answer 1

@JasonStone-1737 , Summarizing the answer from our discussion in the comments section.

Requirement:

The requirement is to store the connection string for Cosmos DB as an environment variable in Azure App Service for an ASP.NET Core application.

Scenario:

When attempting to store the Cosmos DB connection string as an environment variable in Azure App Service, specifically using the "Connection Strings" feature, the configuration retrieval process for the connection string encounters difficulties.

Issue:

Despite attempts to store the Cosmos DB connection string as an environment variable using the "Connection Strings" feature of Azure App Service, the retrieval of the connection string through calls from Microsoft.Extensions.Configuration methods, such as IConfiguration.GetConnectionString() or IConfiguration.GetSection(), returns null values.

Potential Cause:

The cause of the issue lies in the mismatch between the way Azure App Service handles "Connection Strings" and the configuration retrieval mechanism in the ASP.NET Core application using Microsoft.Extensions.Configuration. The discrepancy may be related to the specific configuration setup or version compatibility issues.

Resolution:

To resolve the issue, it is suggested to store the Cosmos DB connection string as an "App Setting" environment variable instead of using the "Connection Strings" feature.

View the Azure Cosmos DB keys in application settings

Storing the connection string as an "App Setting" allows for successful retrieval using IConfiguration.GetSection(). This approach ensures compatibility and successful configuration retrieval within the ASP.NET Core application running on Azure App Service.

-This doc outlines the steps to leverage Connection string prefixes in ASP.NET Core.

Additionally, review and consider updating the application to the latest .NET Core version to address any potential issues or improvements in the configuration code related to Azure App Service integration.

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How do you use a Cosmos connection string in Azure App Service?

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