How to load polymorphic objects in appsettings.json

The key to answer this question is to know how the keys are generated. In your case, the key / value pairs will be:

DynamicConfig:Features:0:TypeDynamicConfig:Features:0:Options:MaxFileSizeDynamicConfig:Features:1:TypeDynamicConfig:Features:1:Options:MinAgeDynamicConfig:Features:1:Options:MaxAgeDynamicConfig:Features:2:TypeDynamicConfig:Features:2:Options:MinAgeDynamicConfig:Features:2:Options:MaxAge

Notice how each element of the array is represented by DynamicConfig:Features:{i}.

The second thing to know is that you can map any section of a configuration to an object instance, with the ConfigurationBinder.Bind method:

var conf = new PersonCheckerOption();Configuration.GetSection($"DynamicConfig:Features:1:Options").Bind(conf);

When we put all this together, we can map your configuration to your data structure:

services.Configure<FeaturesOptions>(opts =>{    var features = new List<FeatureConfig>();    for (var i = 0; ; i++)    {        // read the section of the nth item of the array        var root = $"DynamicConfig:Features:{i}";        // null value = the item doesn't exist in the array => exit loop        var typeName = Configuration.GetValue<string>($"{root}:Type");        if (typeName == null)            break;        // instantiate the appropriate FeatureConfig         FeatureConfig conf = typeName switch        {            "FileSizeChecker" => new FileSizeCheckerOptions(),            "PersonChecker" => new PersonCheckerOption(),            _ => throw new InvalidOperationException($"Unknown feature type {typeName}"),        };        // bind the config to the instance        Configuration.GetSection($"{root}:Options").Bind(conf);        features.Add(conf);    }    opts.Features = features.ToArray();});

Note: all options must derive from FeatureConfig for this to work (e.g. public class FileSizeCheckerOptions : FeatureConfig). You could even use reflection to automatically detect all the options inheriting from FeatureConfig, to avoid the switch over the type name.

Note 2: you can also map your configuration to a Dictionary, or a dynamic object if you prefer; see my answer to Bind netcore IConfigurationSection to a dynamic object.