# Deployment diagram

Deployment diagrams map software onto infrastructure: which artefact runs on which node, and what the nodes are. They answer questions component diagrams cannot.

Useful whenever "where does this actually run?" has taken more than one message to answer.

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## When to draw one

* Documenting an environment for people who will operate it.
* Comparing environments where they genuinely differ.
* Capacity and resilience discussions.

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## What is on the diagram

| **Element**           | **Meaning**                                                   |
| --------------------- | ------------------------------------------------------------- |
| Node                  | A device or execution environment: a server, a container host |
| Artifact              | A deployable thing: a jar, an image, a bundle                 |
| Execution environment | A runtime inside a node: a JVM, a container runtime           |
| Communication path    | A line between nodes, labelled with the protocol              |

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## A worked example

Artefacts placed on nodes, with protocols on the links:

![Deployment diagram](https://help.gocapable.com/images/att1417838621.svg)

The source, which you can paste into a new diagram and edit:

```
@startuml
node "Load balancer" as LB

node "App cluster" {
  node "app-node-1" {
    artifact "api:2.4.0" as A1
    artifact "worker:2.4.0" as W1
  }
  node "app-node-2" {
    artifact "api:2.4.0" as A2
  }
}

database "Postgres primary" as PG
database "Postgres replica" as PGR
node "Redis" as R

LB --> A1 : HTTPS
LB --> A2 : HTTPS
A1 --> PG : TCP 5432
A2 --> PG : TCP 5432
A1 --> R : TCP 6379
W1 --> PG : TCP 5432
PG --> PGR : streaming replication
@enduml
```

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## A few things that catch people out

* Put versions on artefacts. A deployment diagram without them describes an aspiration.
* Label the protocol and port on communication paths; that is what firewall reviews need.
* One diagram per environment, or one diagram with the differences annotated.

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## Related

[Object diagramInstances at a moment in time.](https://help.gocapable.com/diagrams/object-diagram.html)

[Package diagramModules, and which depends on which.](https://help.gocapable.com/diagrams/package-diagram.html)

[UML diagramsBack to the UML overview.](https://help.gocapable.com/diagrams/uml-diagrams.html)

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_Four types cover most of it._