Program.cs

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using System;
using System.Threading.Tasks;

namespace CloudflareDDNSUpdater;

internal class Program {
    private static async Task Main() {
        IConfiguration configuration = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
            .Build();

        var serviceProvider = new ServiceCollection()
            .AddLogging(builder => {
                builder.AddSimpleConsole(options => {
                    options.TimestampFormat = "dd MMM hh:mm:ss ";
                });

                builder.AddConfiguration(configuration);
            })
            .AddTransient<DnsUpdater>()
            .AddTransient(p => configuration)
            .BuildServiceProvider();

        while (true) {
            var dnsUpdater = serviceProvider.GetService<DnsUpdater>();
            var logger = serviceProvider.GetService<ILogger<Program>>();

            try {
                await dnsUpdater.Update();
            }
            catch (Exception ex) {
                logger.LogError(ex, "Error during DNS update");
            }

            logger.LogTrace("Waiting for next update");

            await Task.Delay(TimeSpan.FromMinutes(15));
        }
    }
}