The question requires testing the new application against the full production load before launching it. Traffic mirroring (option D) allows copying live traffic to the new version without directing user requests to it. This enables performance testing under the same load as production without impacting users. Canary (A) and rolling updates (C) gradually shift traffic, not full load. Blue/green (B) typically switches all traffic at once but doesn't test the new version under full load before the switch unless combined with mirroring. Thus, D is the correct choice.