docs: Add Argo CD Core documentation (#13225)

* docs: Add Argo CD Core documentation Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> * docs: Add Argo CD usage to the docs Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> * docs: add Redis details in Argo CD Core doc Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> * docs: minor fix Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> * Address review comments Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> * minor fix Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> * Address review comments Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> * minor fix Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com> --------- Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com>
argoproj · Apr 15, 2023 · c7f8ddd · c7f8ddd
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diff --git a/docs/assets/argocd-core-components.png b/docs/assets/argocd-core-components.png
diff --git a/docs/operator-manual/core.md b/docs/operator-manual/core.md
@@ -0,0 +1,99 @@
+# Argo CD Core
+
+## Introduction
+
+Argo CD Core is a different installation that runs Argo CD in headless
+mode. With this installation, you will have a fully functional GitOps
+engine capable of getting the desired state from Git repositories and
+applying it in Kubernetes.
+
+The following groups of features won't be available in this
+installation:
+
+- Argo CD RBAC model
+- Argo CD API
+- OIDC based authentication
+
+The following features will be partially available (see the
+[usage](#using) section below for more details):
+
+- Argo CD Web UI
+- Argo CD CLI
+- Multi-tenancy (strictly GitOps based on git push permissions)
+
+A few use-cases that justify running Argo CD Core are:
+
+- As a cluster admin, I want to rely on Kubernetes RBAC only.
+- As a devops engineer, I don't want to learn a new API or depend on
+  another CLI to automate my deployments. I want instead rely in
+  Kubernetes API only.
+- As a cluster admin, I don't want to provide Argo CD UI or Argo CD
+  CLI to developers.
+
+## Architecture
+
+Because Argo CD is designed with a component based architecture in
+mind, it is possible to have a more minimalist installation. In this
+case fewer components are installed and yet the main GitOps
+functionality remains operational.
+
+In the diagram below, the Core box, shows the components that will be
+installed while opting for Argo CD Core:
+
+![Argo CD Core](../assets/argocd-core-components.png)
+
+Note that even if the Argo CD controller can run without Redis, it
+isn't recommended. The Argo CD controller uses Redis as an important
+caching mechanism reducing the load on Kube API and in Git. For this
+reason, Redis is also included in this installation method.
+
+## Installing
+
+Argo CD Core can be installed by applying a single manifest file that
+contains all the required resources.
+
+Example:
+
+```
+export ARGOCD_VERSION=<desired argo cd release version (e.g. v2.7.0)>
+kubectl create namespace argocd
+kubectl apply -n argocd -f https://raw.githubusercontent.com/argoproj/argo-cd/$ARGOCD_VERSION/manifests/core-install.yaml
+```
+
+## Using
+
+Once Argo CD Core is installed, users will be able to interact with it
+by relying on GitOps. The available Kubernetes resources will be the
+`Application` and the `ApplicationSet` CRDs. By using those resources,
+users will be able to deploy and manage applications in Kubernetes.
+
+It is still possible to use Argo CD CLI even when running Argo CD
+Core. In this case, the CLI will spawn a local API server process that
+will be used to handle the CLI command. Once the command is concluded,
+the local API Server process will also be terminated. This happens
+transparently for the user with no additional command required. Note
+that Argo CD Core will rely only on Kubernetes RBAC and the user (or
+the process) invoking the CLI needs to have access to the Argo CD
+namespace with the proper permission in the `Application` and
+`ApplicationSet` resources for executing a given command.
+
+To use Argo CD CLI in core mode, it is required to pass the `--core`
+flag with the `login` subcommand.
+
+Example:
+
+```bash
+kubectl config set-context --current --namespace=argocd # change current kube context to argocd namespace
+argocd login --core
+```
+
+Similarly, users can also run the Web UI locally if they prefer to
+interact with Argo CD using this method. The Web UI can be started
+locally by running the following command:
+
+```
+argocd admin dashboard -n argocd
+```
+
+Argo CD Web UI will be available at `http://localhost:8080`
+
diff --git a/docs/operator-manual/installation.md b/docs/operator-manual/installation.md
@@ -48,19 +48,17 @@ High Availability installation is recommended for production use. This bundle in
 
 ## Core
 
-The core installation is most suitable for cluster administrators who independently use Argo CD and don't need multi-tenancy features. This installation
-includes fewer components and is easier to setup. The bundle does not include the API server or UI, and installs the lightweight (non-HA) version of each component.
+The Argo CD Core installation is primarily used to deploy Argo CD in
+headless mode. This type of installation is most suitable for cluster
+administrators who independently use Argo CD and don't need
+multi-tenancy features. This installation includes fewer components
+and is easier to setup. The bundle does not include the API server or
+UI, and installs the lightweight (non-HA) version of each component.
 
-The end-users need Kubernetes access to manage Argo CD. The `argocd` CLI has to be configured using the following commands:
+Installation manifest is available at [core-install.yaml](https://github.com/argoproj/argo-cd/blob/master/manifests/core-install.yaml).
 
-```bash
-kubectl config set-context --current --namespace=argocd # change current kube context to argocd namespace
-argocd login --core
-```
-
-The Web UI is also available and can be started using the `argocd admin dashboard` command.
-
-Installation manifests are available at [core-install.yaml](https://github.com/argoproj/argo-cd/blob/master/manifests/core-install.yaml).
+For more details about Argo CD Core please refer to the [official
+documentation](./core.md)
 
 ## Kustomize
 
@@ -97,4 +95,4 @@ For example if the latest minor version of ArgoCD are 2.4.3 and 2.3.5  while sup
 * Argo CD 2.4.3 on Kubernetes 1.22
 * Argo CD 2.3.5 on Kubernetes 1.24
 * Argo CD 2.3.5 on Kubernetes 1.23
-* Argo CD 2.3.5 on Kubernetes 1.22
+* Argo CD 2.3.5 on Kubernetes 1.22
diff --git a/mkdocs.yml b/mkdocs.yml
@@ -21,6 +21,7 @@ nav:
   - operator-manual/index.md
   - operator-manual/architecture.md
   - operator-manual/installation.md
+  - operator-manual/core.md
   - operator-manual/declarative-setup.md
   - operator-manual/app-any-namespace.md
   - operator-manual/ingress.md