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Software Architecture Guide

Deployment View

Explanation

Section titled “Explanation”

A deployment view describes the infrastructure under your system. It shows which building blocks run on which hardware. arc42 covers it in chapter 7, the Deployment View.

Why document it. The infrastructure under a system can influence the system. It can also influence its cross-cutting concepts. These are ideas that apply across many parts of the system (see the article Crosscutting Concept). Because of this influence, the infrastructure needs documentation.

How to express it. arc42 suggests UML deployment diagrams. UML is a standard modeling language. See the article UML Deployment Diagram for the notation.

The mapping. arc42 tip 7-5 says to document the mapping of building blocks onto hardware. A building block is a part of the system, such as a service or a database. The mapping states where each one runs.

Several environments. Some systems run in more than one environment. In that case, arc42 advises documenting all relevant environments.

Infrastructure nodes. The C4 model has a similar deployment diagram. It can show infrastructure nodes next to deployment nodes. Examples are DNS services, load balancers and firewalls. A load balancer spreads incoming requests across several servers (see the article Load Balancer).

Example

Section titled “Example”

A team builds an online shop. Its deployment diagram shows a web server node running the shop application and a database node running the order database. A load balancer and a firewall sit in front of the web server. The team draws a second diagram for the test environment, which is set up differently.

Trade-offs

Section titled “Trade-offs”

The verified facts name no explicit trade-offs. One practical consequence follows from arc42’s advice: every additional environment you document means more deployment content to write and keep current.

A generic deployment diagram: building blocks mapped onto nodes.

Diagram source 
@startuml
node "Load Balancer" as lb
node "Web Server" as web {
  artifact "shop-app"
}
node "Database Server" as db {
  artifact "order-db"
}
lb --> web
web --> db
@enduml

Checks

Section titled “Checks”
  • The document maps building blocks onto hardware.
  • If the system runs in several environments, each relevant environment is documented.
  • The deployment view uses a UML deployment diagram.
  • The document explains how the infrastructure influences the system or its cross-cutting concepts.
Section titled “Related”

Sources

Section titled “Sources”