94 lines
3.2 KiB
Markdown
94 lines
3.2 KiB
Markdown
---
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stage: none
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group: unassigned
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info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
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---
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# Backend directory structure
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## Use namespaces to define bounded contexts
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A healthy application is divided into macro and sub components that represent the contexts at play,
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whether they are related to business domain or infrastructure code.
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As GitLab code has so many features and components it's hard to see what contexts are involved.
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We should expect any class to be defined inside a module/namespace that represents the contexts where it operates.
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When we namespace classes inside their domain:
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- Similar terminology becomes unambiguous as the domain clarifies the meaning:
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For example, `MergeRequests::Diff` and `Notes::Diff`.
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- Top-level namespaces could be associated to one or more groups identified as domain experts.
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- We can better identify the interactions and coupling between components.
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For example, several classes inside `MergeRequests::` domain interact more with `Ci::`
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domain and less with `ImportExport::`.
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```ruby
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# bad
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class MyClass
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end
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# good
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module MyDomain
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class MyClass
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end
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end
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```
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### About namespace naming
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A good guideline for naming a top-level namespace (bounded context) is to use the related
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[feature category](https://gitlab.com/gitlab-com/www-gitlab-com/-/blob/master/data/categories.yml). For example, `Continuous Integration` feature category maps to `Ci::` namespace.
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Alternatively a new class could be added to `Projects::` or `Groups::` if it's either:
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- Strictly related to one of these domains. For example `Projects::Alias`.
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- A new component that does not have yet a more specific domain. In this case, when
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a more explicit domain does emerge we would need to move the class to a more specific
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namespace.
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Do not use the [stage or group name](https://about.gitlab.com/handbook/product/categories/#devops-stages)
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since a feature category could be reassigned to a different group in the future.
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```ruby
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# bad
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module Create
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class Commit
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end
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end
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# good
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module Repositories
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class Commit
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end
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end
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```
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On the other hand, a feature category may sometimes be too granular. Features tend to be
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treated differently according to Product and Marketing, while they may share a lot of
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domain models and behavior under the hood. In this case, having too many bounded contexts
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could make them shallow and more coupled with other contexts.
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Bounded contexts (or top-level namespaces) can be seen as macro-components in the overall app.
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Good bounded contexts should be [deep](https://medium.com/@nakabonne/depth-of-module-f62dac3c2fdb)
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so consider having nested namespaces to further break down complex parts of the domain.
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For example, `Ci::Config::`.
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For example, instead of having separate and granular bounded contexts like: `ContainerScanning::`,
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`ContainerHostSecurity::`, `ContainerNetworkSecurity::`, we could have:
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```ruby
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module ContainerSecurity
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module HostSecurity
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end
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module NetworkSecurity
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end
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module Scanning
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end
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end
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```
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If classes that are defined into a namespace have a lot in common with classes in other namespaces,
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chances are that these two namespaces are part of the same bounded context.
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