Dependencies

Introduction

A dependency is the edge between two nodes that describes their relationship. It can be one of three types,

• Parent
  A node is the parent of another node, meaning it must exist before the child node is created. For example, an app is the parent of a region, so the app must exist before any region is created.
• Child
  A node is the child of another node, meaning it will be deleted before the parent node is deleted. For example, an environment is a child of a region, so all environments must be deleted before deleting the region.
• Relationship
  A node has a relationship with another node that is neither a parent nor a child relationship. For example, a server could have a relationship with an image. The distinction between the "relationship" type and the "parent-child" type is that in a "relationship", there is no obligation for either node to exist or be deleted before of the other node.

tip

• A parent-child dependency is bidirectional, i.e. if Node 1 is parent of Node 2, then Node 2 must be a child of Node 1.
• A "Relationship" dependency is also bidirectional, i.e. if Node 1 has relationship with Node 2, then Node 2 also has a relationship with Node 1.

Node

A node in Octo can be - a Model, a Resource, or an Overlay.
In Octo code base, a node is represented as an extension of ANode<I, T>, which is the base abstract class that Models, Resources, and Overlays inherit from.

Dependency Class

A dependency is not stored as a property in nodes; instead, it is its own class as a first class citizen. It encompasses two nodes on its either end.

Dependency Schema

{
  from: "a node",
  to: "a node",
  relationship: "parent | child | relationship",
  behaviors: "an array of metadata with individual traits of this dependency."
}

A dependency is also serialized and deserialized just like other nodes. Octo keeps track of all dependencies in a graph in the state files, and are diffed between runs.

Summary

In this section we explored Dependencies. Just as in a typical graph we have vetices and edges, in Octo graphs, nodes are vertices and dependencies are edges. A dependency is a first class citizen of Octo, and has its own dedicated class.