The usage of an API gateway enforces a physical implementation of what so far was only a  logical boundary, based on the social and business notion of the application itself: it mandates  that communication across applications goes through a formal layer, which is the sole  gateway to what’s wrapped within the ownershi p boundary. As a direct consequence, other  microservices that are owned by a different group — and therefore outside of the boundary —  should be able to access application components only via this gateway.  What about the advantages that are provided by a service mesh when it comes to  service-to-service communication? They can all be leveraged — if the mesh is used for communication within the application  boundary — for what we have called intra-application communication. See Figure 4-19 on  page 125. 124  Accelerating Modernization with Agile Integration Figure 4-18 Application boundaries with API gateway  6 H U Y L F H  6 H U Y L F H  6 H U Y L F H  6 H U Y L F H  6 H U Y L F H $ 3 , J D W H Z D \  6 H U Y L F H  6 H U Y L F H  6 H U Y L F H $ 3 , J D W H Z D \  6 H U Y L F H  6 H U Y L F H  6 H U Y L F H $ 3 , J D W H Z D \ $ 3 , J D W H Z D \  6 H U Y L F H $ S S O L F D W L R Q E R X Q G D U \  6 H U Y L F H 0 L F U R V H U Y L F H F R P S R Q H Q W , Q W H U D S S O L F D W L R Q $ 3 , , Q W U D D S S O L F D W L R Q $ 3 ,