asp.net core override connection strings via ENV variables

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.

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

1. 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": "*"
   }
   

2. 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();
       }
   }
   

3. 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

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

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

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

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