asp.net core override connection strings via ENV variables


I have an asp.net core API 2.2 implemented. I have created a docker image. I would like to override connection strings in appsettings.json file.

Is there any way to do it? I tried via environment variables when I start the container with command docker container run -e "ConnectionStrings:DefaultConnection={...here goes the connection string}"

I have also builder.AddEnvironmentVariables(); in my Startup.cs but connection string in my appsetting.json is not replaced.

I checked it inside the container, appsetting.json is there but the values are not replaced.

Any other way how to do such cases? Thx.


For -e, it will override the system environment which will change the connectionstring when you retrive from code, it will not affect the content in appsettings.json.

For example


Assume you have a appsettings.json like

{ "ConnectionStrings": { "DefaultConnection": "Server=(localdb)\\mssqllocaldb;Database=aspnet-TestDockerConfiguration-416C6FD2-3531-42D6-9EDE-18AC45901208;Trusted_Connection=True;MultipleActiveResultSets=true" }, "Logging": { "LogLevel": { "Default": "Warning" } }, "AllowedHosts": "*" } </li> <li>

Retrive the connectionstring by _configuration.GetConnectionString("DefaultConnection") like

public class HomeController : Controller { private readonly IConfiguration _configuration; public HomeController(IConfiguration configuration) { _configuration = configuration; } public IActionResult Index() { return Ok(_configuration.GetConnectionString("DefaultConnection")); //return View(); } } </li> <li>

For docker run -it -p 8888:80 dockerconfiguration, it will return "Server=(localdb)\\mssqllocaldb;Database=aspnet-TestDockerConfiguration-416C6FD2-3531-42D6-9EDE-18AC45901208;Trusted_Connection=True;MultipleActiveResultSets=true" for Index Action

</li> <li>

For docker run -it -p 8888:80 dockerconfiguration -e "ConnectionStrings:DefaultConnection"="testsqlstring", it will return testsqlstring

</li> <li>

So, if you only want to override the value in appsettings.json during runtime, you just need to specify like Step 4

</li> </ol>

If you prefer change the appsettings.json file in docker container, you could follow steps below

<ol><li>Install vi command with apt-get install vim -y</li> <li>Run docker exec -it 43ea835776dd /bin/bash to go into container </li> <li>Run ls to list files and find the appsettings.json</li> <li>Run vi appsettings.json to modify the content</li> <li>Run cat appsettings.json to check the content whether it is changed</li> <li>Run exit and access the Home/Index to check the result.</li> </ol>

appsetting.json never gets changed, however based on the hierarchy, variables values get overridden. Take a look at the examples at https://docs.microsoft.com/en-us/aspnet/core/fundamentals/configuration/?view=aspnetcore-2.2#conventions . It works pretty well. Perhaps just to be sure that you didn't break something because of command line execution, you can try to assign environment variables via docker-compose. The rule of thumb is that the pattern that you use for the "key" must match (with the help of __ instead of :)what you have in the json file, so that it gets overridden.



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