how override appsetting values from docker in asp.net core 3.1?

Question

I made an asp.net core project,but i have question,how override app-setting values after container built? my appsetting:

  "AppSetting": {
    "RabbitMqUrl": "rabbitmq://localhost/",
    "RabbitMqUserName": "guest",
    "RabbitMqPassword": "guest",
    "LoginMessage": "x",
    "ResetPasswordMessage": "x",
    "myval": 10
  }

I find this command but i want see and change myval value when container is running in for example in restart container command,how do these items?

   docker run -it -p 5005:5005 -e "AppSetting:myval=123" identity

Roar S. · Accepted Answer · 2020-08-16 17:09:54Z

1

UPDATE: After some clearification, question is about changing environment vars run-time. That is not a very good idea. For sharing application-wide variables that may change, a cache is a viable solution.

In Startup#ConfigureServices

services.AddDistributedMemoryCache();

Then you can inject

IMemoryCache

into your code. You can add/change cache value like this

_cache.Set("myval", 123, DateTimeOffset.MaxValue);

and the value will stay in cache until end of time (or until your code changes/removes it). You fetch data from cache like this

var myVal = 0;
if (_cache.TryGetValue("myval", out int value))
{
   myVal = value;
}

If you need to initialize the cache with some value from appsettings.json, that can be done inside Program#Main after webHost is built, and before calling webHost.Run / webHost.RunAsync.

END of update

Unless you have a class called AppSetting, json should look like below. You should have an appsettings.json that applies to all environments, an appsettings.Staging.json for staging, and an appsettings.Production.json for production.

{
  "RabbitMqUrl": "rabbitmq://localhost/",
  "RabbitMqUserName": "guest",
  "RabbitMqPassword": "guest",
  "LoginMessage": "x",
  "ResetPasswordMessage": "x",
  "myval": 10
}

You select running enviroment in Docker file like this

ENV ASPNETCORE_ENVIRONMENT Production

You can override parameters in appsettings.json like this

 ENV ASPNETCORE_myval 123

If you stick with your original JSON structure:

ENV ASPNETCORE_AppSetting__myval 123

edited Aug 16, 2020 at 17:09

answered Aug 15, 2020 at 16:11

Roar S.

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2 Comments

Ali.goodarzi Over a year ago

thanks roar, i want this value change in runtime or like this command docker run -it -p 5005:5005 -e "AppSetting:myval=123" identity ,i dont want create new instanse from my image ,but apply this change on current container.

Roar S. Over a year ago

@Ali.goodarzi: Ok, sorry for the misunderstanding. But you should not do it like that, settings are static stuff that is used for getting the app up-and-running. I will update my answer with more code.

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