ElasticsearchExtensions.cs

public static class ElasticsearchExtensions
{
	public static void AddElasticsearch(this IServiceCollection services, IConfiguration configuration)
	{
		var settings = new ConnectionSettings(new Uri(configuration["ElasticsearchSettings:uri"]));

		var defaultIndex = configuration["ElasticsearchSettings:defaultIndex"];

		if (!string.IsNullOrEmpty(defaultIndex))
			settings = settings.DefaultIndex(defaultIndex);

		var basicAuthUser = configuration["ElasticsearchSettings:username"];
		var basicAuthPassword = configuration["ElasticsearchSettings:password"];

		if (!string.IsNullOrEmpty(basicAuthUser) && !string.IsNullOrEmpty(basicAuthPassword))
			settings = settings.BasicAuthentication(basicAuthUser, basicAuthPassword);

		settings.EnableApiVersioningHeader();
		settings.EnableHttpCompression();

		var client = new ElasticClient(settings);

		services.AddSingleton<IElasticClient>(client);
	}
}