how it works application configuration

Application Configuration

There's one nuget package I found through research named ConfigurationSubstitutor by molinch

This allows for self-configured configuration and substitutions

Here's where it's added in the code

builder.Configuration.EnableSubstitutionsWithDelimitedFallbackDefaults("$(", ")", " ?? ");

In order for ConfigurationSubstitutor to configure app settings [using the syntax I provided], substitutions must start with "$(" and end with ")"

On top of that, a familiar delimited fallback default syntax is configured [familiar to C# developers at least] and resembles the null-coalescing operator

Here's a sample of its usage in the health checks ui

{
    "Host": "localhost",
    "Applications": {
        "Mvc": "http://$(Host):5001",
        "WebBff": "http://$(Host):5050",
        "AddressService": "http://$(Host):5011",
        "AddressWorker": "http://$(Host):5021",
        "IdentityService": "http://$(Host):5005",
        "OrderService": "http://$(Host):5012",
        "OrderWorker": "http://$(Host):5022",
        "TyresService": "http://$(Host):5013"
    }
}

The Host app setting is used to configure all the application endpoints

This is how the configured values would look like when retrieved from configuration

{
    "Applications": {
        "Mvc": "http://localhost:5001",
        "WebBff": "http://localhost:5050",
        "AddressService": "http://localhost:5011",
        "AddressWorker": "http://localhost:5021",
        "IdentityService": "http://localhost:5005",
        "OrderService": "http://localhost:5012",
        "OrderWorker": "http://localhost:5022",
        "TyresService": "http://localhost:5013"
    }
}

In docker-compose, the Host app setting is overridden using an environment variable with its value set to host.docker.internal

App settings will then be configured like this

{
    "Applications": {
        "Mvc": "http://host.docker.internal:5001",
        "WebBff": "http://host.docker.internal:5050",
        "AddressService": "http://host.docker.internal:5011",
        "AddressWorker": "http://host.docker.internal:5021",
        "IdentityService": "http://host.docker.internal:5005",
        "OrderService": "http://host.docker.internal:5012",
        "OrderWorker": "http://host.docker.internal:5022",
        "TyresService": "http://host.docker.internal:5013"
    }
}

Here's an example of how the delimited default is used

{
    "LoggingSinks": {
        "Elasticsearch": {
            "Enabled": "$(envUseElasticsearch ?? false)",
            "Url": "$(envElasticsearchUrl ?? http://localhost:9201)"
        }
    }
}

Let's assume there's no environment variables available to override, this is what the result will be

{
    "LoggingSinks": {
        "Elasticsearch": {
            "Enabled": false,
            "Url": "http://localhost:9201"
        }
    }
}

In docker-compose, those environment variables are provided and therefore overrides the values in app settings

• envUseElasticsearch = true
• envElasticsearchUrl = http://elasticsearch:9200

The resulting configuration looks like this

{
    "LoggingSinks": {
        "Elasticsearch": {
            "Enabled": true,
            "Url": "http://elasticsearch:9200"
        }
    }
}

Additional Resources

• Configuration in ASP.NET Core