Within those tiers, a well-designed application is broken down internally into separate  components that are responsible for each of the application’s functions. However, they still all  run in the same application server runtime. Software development and architecture approaches like 12-factor and microservices started  to advocate for those components to become truly independent. Ideally, they would be  completely decoupled from each other down to the network level. This is shown in  Figure 4-10. With these changes in application architectures, an issue started to surface: how to define an  application boundary. For monolithic applications the logical boundary of the application corresponded with the  physical implementation of the application itself. After the application components become  truly decoupled and independently deployed, the boundary is no longer implicitly present.  Therefore, if a boundary must exist to group all the application components in a single logical  construct, that boundary must be explicitly identified and designed in. It might be tempting to think that we could dispense with application boundaries altogether  and simply manage business functions granularly. However, anyone with experience of even  a moderately sized IT landscape recognizes that clear ownership is required at a much more  114  Accelerating Modernization with Agile Integration 4.7.2 Why do application boundaries matter? Figure 4-10 Separate components that run in the same application server runtime Silo Applications Silo Applications 0 L F U R V H U Y L F H S O D W I R U P 3 U H V H Q W D W L R Q ' D W D / R J L F  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  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  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  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  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  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  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  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  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  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  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  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  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  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  6 H U Y L F H  6 H U Y L F H ) X O O \ U H I D F W R U H G D S S O L F D W L R Q V 3 D U W L D O O \ U H I D F W R U H G D S S O L F D W L R Q V 3 U H V H Q W D W L R Q ' D W D / R J L F 1 H Z D S S O L F D W L R Q V  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  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  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  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  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