How is irony used in the Kite Runner?

Hosseini is in the irony business. For example: Isn't it ironic that Baba also betrayed his friend even though he talks big about honor and principles? Isn't it ironic that Assef finally loses his eye? Isn't it ironic that Amir gets a scar on his lip just like Hassan? Isn't it ironic when Amir, who ends up being Hassan's half-brother, says things like "[t]he curious thing was, I never thought of Hassan and me as friends [...]" (4.4)? The irony adds yet another edge to the story; it gives the more sentimental passages backbone. In the end, The Kite Runner is such a tearjerker, such an emotional tour de force, because it shifts between these three tones.