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docs: Add Argo CD components architecture doc (#13194)
* docs: Add Argo CD components architecture doc Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> * docs: update diagram Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> * docs: add component arch doc Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> * reformat doc Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> * Add component doc in the menu Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> * update image Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> * Update docs/developer-guide/architecture/components.md Co-authored-by: Michael Crenshaw <350466+crenshaw-dev@users.noreply.github.com> Signed-off-by: Leonardo Luz Almeida <leoluz@users.noreply.github.com> * Update docs/developer-guide/architecture/components.md Co-authored-by: Michael Crenshaw <350466+crenshaw-dev@users.noreply.github.com> Signed-off-by: Leonardo Luz Almeida <leoluz@users.noreply.github.com> * Update docs/developer-guide/architecture/components.md Co-authored-by: Michael Crenshaw <350466+crenshaw-dev@users.noreply.github.com> Signed-off-by: Leonardo Luz Almeida <leoluz@users.noreply.github.com> --------- Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> Signed-off-by: Leonardo Luz Almeida <leoluz@users.noreply.github.com> Co-authored-by: Michael Crenshaw <350466+crenshaw-dev@users.noreply.github.com>
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docs/developer-guide/architecture/components.md
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# Component Architecture
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Argo CD is designed with a component based architecture. The goal is
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to separate the responsibility in different deployable units in order
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to have the following benefits:
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- **Modularity**: Provides great level of flexibility. Components
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interact with each other via an interface. This means that as long
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as the interface contract is respected, a given component can be
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replaced without requiring the rest of the system to adapt. It is
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also possible to run the system without certain components if a
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specific group of functionality isn't desired.
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- **Single responsibility**: Helps to determine where the different
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types of functionality should be implemented which drives for
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better system cohesiveness.
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- **Reusability**: Clearly defined interfaces helps in functionality
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discoverability which benefits reusability of services.
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The default Argo CD installation is composed by different components
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and different Kubernetes controllers. The controllers aren't
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categorized as components as they have proprietary interfaces (CRDs)
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and therefore, miss the modular nature. There are more resources
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created while installing Argo CD (ConfigMaps, Services, etc), but for
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simplicity we are covering just the ones directly related with the
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componentized architecture.
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## Dependencies
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The diagram below has represented all dependencies between the
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different components used by the default Argo CD installation:
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There are 4 logical layers represented in the diagram:
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- **UI**: This is the presentation layer. Users interact with Argo CD
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mainly by components from this layer.
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- **Application**: The capabilities required to support the components
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from the UI layer.
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- **Core**: The main Argo CD gitops functionality is implemented by
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components and Kubernetes controllers from the Core layer.
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- **Infra**: Represent the tools that Argo CD depends on as part of
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its infrastructure.
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The logical layers also help making the diagram easier to follow as
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dependencies are represented in a top-down relationship. This means
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that components from the top layers will be allowed to depend on any
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component from any of the bottom layers. However components from the
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bottom layers will never depend on any ones from upper layers.
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## Responsibility
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Below you can refer to a brief description of Argo CD components and
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its main responsibilities.
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### Webapp
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Argo CD ships with a powerful web interface that allows managing
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applications deployed in a given Kubernetes cluster.
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### CLI
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Argo CD provides a CLI that can be used by users to interact with Argo
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CD API. The CLI can also be used for automation and scripting.
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### API Server
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Defines the proprietary API exposed by Argo CD that powers the Webapp
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and the CLI functionalities.
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### Application Controller
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The Application Controller is responsible for reconciling the
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Application resource in Kubernetes syncronizing the desired
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application state (provided in Git) with the live state (in
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Kubernetes). The Application Controller is also responsible for
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reconciling the Project resource.
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### ApplicationSet Controller
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The ApplicationSet Controller is responsible for reconciling the
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ApplicationSet resource.
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### Repo Server
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Repo Server plays an important role in Argo CD architecture as it is
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responsible for interacting with the Git repository to generate the
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desired state for all Kubernetes resources that belongs to a given
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application.
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### Redis
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Redis is used by Argo CD to provide a cache layer reducing requests
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sent to the Kube API as well as to the Git provider. It also supports
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a few UI operations.
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### Kube API
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Argo CD controllers will connect to the Kubernetes API in order to run
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the reconciliation loop.
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### Git
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As a gitops tool Argo CD requires that the desired state of the
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Kubernetes resources to be provided in a Git repository.
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We use "git" here to stand in for an actual git repo, a Helm repo,
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or an OCI artifact repo. Argo CD supports all those options.
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### Dex
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Argo CD relies on Dex to provide authentication with external OIDC
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providers. However other tools can be used instead of Dex. Check the
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[user management
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documentation](../../operator-manual/user-management/index.md) for
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more details.
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@@ -171,6 +171,7 @@ nav:
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- developer-guide/index.md
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- Architecture:
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- developer-guide/architecture/authz-authn.md
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- developer-guide/architecture/components.md
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- Code Contribution Guide: developer-guide/code-contributions.md
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- Toolchain Guide: developer-guide/toolchain-guide.md
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- developer-guide/contributors-quickstart.md
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