checkdb.cs

app.Use(async (context, func) =>
{
    if (context.Request.Path.Value == "/hc")
    {
        try
        {
            using (var db = new SqlConnection("Database=Oops"))
            {
                await db.OpenAsync();
                db.Close();
            }

            context.Response.StatusCode = 200;
            context.Response.ContentLength = 2;
            await context.Response.WriteAsync("UP");
        }
        catch (SqlException)
        {
            context.Response.StatusCode = 400;
            context.Response.ContentLength = 20;
            await context.Response.WriteAsync("SQL Connection Error");
        } 
    }
    else
    {
        await func.Invoke();
    }
});