Increase upload file size in ASP.NET core

In the case of a .NET CORE application, the configuration can be achieved in a much more easier manner. The easiest way to do this, would be to add the RequestSizeLimit Attribute to the Model. For example:

[RequestSizeLimit(5*1024*1024)]     // set the maximum file size limit to 5 MB
public class InputModel 
{
    ...
}

It would also help adopting a Validation Attribute to verify the uploaded file size is limited to the specific size you are seeking. For example:

namespace MyApp.Validators
{
    using Microsoft.AspNetCore.Http;
    using System.ComponentModel.DataAnnotations;

    [AttributeUsage(
        validOn: AttributeTargets.Field | AttributeTargets.Property, 
        AllowMultiple = false, 
        Inherited = true)]
    public class MyUploadFileSizeValidator
        : ValidationAttribute
    {
        public MyUploadFileSizeValidator(long sizeInBytes)
        {
            this.SizeInBytes = sizeInBytes;
        }

        public long SizeInBytes { get; private set; }


        /// <summary>  
        ///     Validates the specified value with respect to the current validation attribute
        /// </summary>  
        /// <param name="value">the value to validate</param>  
        /// <returns>Returns - true to specify size is okay.</returns> 
        public override bool IsValid(object value)
        {
            bool isValid = false;

            // NOTE: Use HttpPostedFileBase instead of IFormFile in ASP.NET MVC
            if (value is IFormFile file)
            {
                isValid = file.Length <= this.SizeInBytes;
            }

            return isValid;
        }

    }
}

and then, just use it on the property of the Model. So, your model would look something like this:

[RequestSizeLimit(5*1024*1024)]     // set the maximum file size limit to 5 MB
public class InputModel
{
    [Required(ErrorMessage = "Please select an image file to upload.")]
    [MyUploadFileSizeValidator(sizeInBytes: 5 * 1024 * 1024, 
                               ErrorMessage = "Image filesize should be smaller than 5 MB")]
    [Display(Name = "Profile Photo")]
    public IFormFile ProfilePhoto { get; set; }
}

Hope this helps.