Question

When I update product like price or name on back-end, I want front-end users access only one page in a site: informing page with content: ‘We’re updating products, please comeback later’. And some client who is buying products with action: Add to cart or go to cart will be cancel and redirect to informing page

Answer 1

I agree with the comment placed by josh3736, that you may wish to rethink it.

However one way you can look at implementing this is by overriding the BeginRequest method in the global.asax file

    protected void Application_BeginRequest(object sender, EventArgs e)
    {
       if(ShouldIShowMessage())
       {
           this.Response.Redirect("RedirectUrl");
       }
    }

    private bool ShouldIShowMessage()
    {
       // Decision logic here
    }