C#•12mo ago

Overriding appsettings.json section with environment variable

Given a configuration section called

Tenants

Tenants

Tenants

Tenants, I'd like to override it with a whole JSON structure via an environment variable.

Given I want this

"Tenants": {
  "ByCode": {
    "11": {
      "Name": "acme"
    },
    "42": {
      "Name": "silver"
    }
  }
}

"Tenants": {
  "ByCode": {
    "11": {
      "Name": "acme"
    },
    "42": {
      "Name": "silver"
    }
  }
}

"Tenants": {
  "ByCode": {
    "11": {
      "Name": "acme"
    },
    "42": {
      "Name": "silver"
    }
  }
}

"Tenants": {
  "ByCode": {
    "11": {
      "Name": "acme"
    },
    "42": {
      "Name": "silver"
    }
  }
}

I'm doing

export Tenants='{"ByCode": {"11": {"Name": "acme"}, "42": {"Name": "silver"}}}'

export Tenants='{"ByCode": {"11": {"Name": "acme"}, "42": {"Name": "silver"}}}'

export Tenants='{"ByCode": {"11": {"Name": "acme"}, "42": {"Name": "silver"}}}'

export Tenants='{"ByCode": {"11": {"Name": "acme"}, "42": {"Name": "silver"}}}'

I'm trying to bind it against an object with the options pattern:

builder.Services.Configure<TenantsOptions>(
        builder.Configuration.GetSection(TenantsOptions.SectionName));

builder.Services.Configure<TenantsOptions>(
        builder.Configuration.GetSection(TenantsOptions.SectionName));

builder.Services.Configure<TenantsOptions>(
        builder.Configuration.GetSection(TenantsOptions.SectionName));

builder.Services.Configure<TenantsOptions>(
        builder.Configuration.GetSection(TenantsOptions.SectionName));

And the classes look like:

public class TenantsOptions
{
    public const string SectionName = "Tenants";

    public Dictionary<string, Tenant> ByCode { get; set; } = new();
}

public class Tenant
{
    public string Name { get; set; }
}

public class TenantsOptions
{
    public const string SectionName = "Tenants";

    public Dictionary<string, Tenant> ByCode { get; set; } = new();
}

public class Tenant
{
    public string Name { get; set; }
}

public class TenantsOptions
{
    public const string SectionName = "Tenants";

    public Dictionary<string, Tenant> ByCode { get; set; } = new();
}

public class Tenant
{
    public string Name { get; set; }
}

public class TenantsOptions
{
    public const string SectionName = "Tenants";

    public Dictionary<string, Tenant> ByCode { get; set; } = new();
}

public class Tenant
{
    public string Name { get; set; }
}

When I run the ASP.NET Core app, the

ByCode

ByCode

ByCode

ByCode dictionary is empty. But if I just paste the JSON section in appsettings.json, it's correctly populated.

For the record, I can see the whole structure if I just log

builder.Configuration.GetSection(TenantsOptions.SectionName).Value;

builder.Configuration.GetSection(TenantsOptions.SectionName).Value;

builder.Configuration.GetSection(TenantsOptions.SectionName).Value;

builder.Configuration.GetSection(TenantsOptions.SectionName).Value;, but for some reason, I guess it's only interpreted as a string, and not correctly deserialized and bound to

TenantOptions

TenantOptions

TenantOptions

TenantOptions?

So how do you actually override a whole section with a JSON value through an environment variable?

FusedQyou•1/9/25, 2:04 PM

I don't see how environment variables apply here

sl8erOP•1/9/25, 2:07 PM

How's that?

FusedQyou•1/9/25, 2:09 PM

I mean I don't see where environment variables are related to your question

FusedQyou•1/9/25, 2:09 PM

Is it that you load appsettings based on the environment?

FusedQyou•1/9/25, 2:10 PM

I suppose you should first check if the resulting configuration from builder.Configuration.GetSection(TenantsOptions.SectionName)builder.Configuration.GetSection(TenantsOptions.SectionName) returns the data you expect

sl8erOP•1/9/25, 2:10 PM

I'm setting an env variable externally before running the app, like I mentioned:

export Tenants='{"ByCode": {"11": {"Name": "acme"}, "42": {"Name": "silver"}}}'export Tenants='{"ByCode": {"11": {"Name": "acme"}, "42": {"Name": "silver"}}}'

FusedQyou•1/9/25, 2:10 PM

You can also try to use GetRequiredSectionGetRequiredSection

FFusedQyou I suppose you should first check if the resulting configuration from `builder.Co...

sl8erOP•1/9/25, 2:10 PM

It does return the data I want, it's just that it doesn't bind to the options object.

sl8erOP•1/9/25, 2:14 PM

Even the documentation on this seems to only mention cases where fields in a JSON object are set independently, rather than setting the whole object via a JSON string.
https://learn.microsoft.com/en-us/aspnet/core/fundamentals/configuration/?view=aspnetcore-9.0#evcp

set Position__Title=Environment_Editor
set Position__Name=Environment_Rick

set Position__Title=Environment_Editor
set Position__Name=Environment_Rick

Configuration in ASP.NET Core

Learn how to use the Configuration API to configure AppSettings in an ASP.NET Core app.

sl8erOP•1/9/25, 2:15 PM

Like instead of doing
export Position='{ "Title": "Environment_Editor", "Name": "Environment_Rick" }'export Position='{ "Title": "Environment_Editor", "Name": "Environment_Rick" }'

becquerel•1/9/25, 2:41 PM

I don't think what you want is supported. My understanding is IConfiguration takes an environment variable as representing a single atom of configuration, not as something that can potentially represent an entire configuration section. If you set the env var to a JSON string, then IConfiguration will consider it as just a

string

string

.

I think the 'right' way to do this would be to set up multiple environment variables to override each property of the structure.

becquerel•1/9/25, 2:41 PM

e.g. export TENANTS__ByCode = ["foo", "bar"]export TENANTS__ByCode = ["foo", "bar"]

Sehra•1/9/25, 2:42 PM

you would have to specify multiple

export Tenants__ByCode__11__Name=acme
export Tenants__ByCode__42__Name=silver

export Tenants__ByCode__11__Name=acme
export Tenants__ByCode__42__Name=silver

Sehra•1/9/25, 2:43 PM

but limitations are that it will get merged, by default with env overriding json, args overriding env

sl8erOP•1/9/25, 2:45 PM

I really feared it wouldn't be supported. Doing export Tenants__ByCode__11__Name=acmeexport Tenants__ByCode__11__Name=acme for the huge actual structure I'm dealing with is really crazy.

sl8erOP•1/9/25, 2:45 PM

Maybe it can be suggested as a potential improvement.

Sehra•1/9/25, 2:46 PM

you can add more json files if you want, add them as optional

becquerel•1/9/25, 2:47 PM

Yeah, I feel like this is a bit of an x/y problem. why do you want to override a big json object with environment variables?

Bbecquerel Yeah, I feel like this is a bit of an x/y problem. why do you want to override a...

sl8erOP•1/9/25, 2:47 PM

It's a Kubernetes secret injected into the environment.

sl8erOP•1/9/25, 2:49 PM

It's not such a novel idea. Other frameworks support this, like Spring. You can override the whole application config with a JSON-inline env variable SPRING_APPLICATION_JSONSPRING_APPLICATION_JSON.

sl8erOP•1/9/25, 2:50 PM

Or just subkeys.

Sehra•1/9/25, 2:54 PM

you could handle it in code by reading that envvar coming in to a dictionary and adding an InMemoryCollection that would override any existing. not possible to delete keys though, it would be merged

wasabi•1/11/25, 12:03 AM

You can certainly write your own ICOnfiguratioSource and Provider.

wasabi•1/11/25, 12:04 AM

BUt if this is K8s, it would be better to just use KubernetesConfigurationProvider.

Overriding appsettings.json section with environment variable

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