Add requirements & basic-architecture doc (#73)

Signed-off-by: Arnob kumar saha <arnob@appscode.com>

Author: ArnobKumarSaha

src/en/guides/get-started/architecture.md

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+---
+layout: 'guide'
+menu:
+  docs_menu:
+    identifier: guide-architecture
+    name: Architecture
+    parent: guide-start
+    weight: 12
+menu_name: docs_menu
+section_menu: guides
+---
+
+# Architecture
+Let's first discuss some basic terminologies, those will be repeated many times throughout the whole docs. The below picture will help in describing the terminologies:
+
+![architecture](images/architecture.png)
+
+### ACE
+ACE is the central management cluster where we will deploy all the ui-components. Namely the `backend server(ace-platform-api)`, `kubedb-ui`, `cluster-ui`, `billing-ui`, `platform-ui`, `grafana-ui`, ingresses etc. This will be mainly used by the administrators & devops engineers. 
+As this is the central point of management, we call it `Management cluster`. As all the UI-components installed in this, we sometimes call `UI cluster`.
+
+We also have native-integration of [OCM hub-spoke model](https://open-cluster-management.io/docs/concepts/architecture/). This is by-default enabled. This integration enables the cluster-manager to easily do similar changes(for example: installing a feature) centrally. 
+ACE is used as the hub of OCM mode. Thats why we call this `Hub cluster` too.
+
+The ACE cluster can be a single-node k3s cluster for staging or development. Or a full-fledged multi-node cluster for prod.
+
+The installer page on the `selfhost-ui` on appscode.com provides instructions for quickly setting up a K3s cluster to get started immediately.
+
+### DBaaS
+DBaaS cluster is the main cluster for database users. This can be of two main type: spoke cluster, general imported cluster.
+While importing, if someone make it a spoke, then cluster-manager-spoke features will be installed by the Hub cluster.
+If you don't want to manage it from the hub, we can just import it as a general cluster. In that case, that auto-sync from hub will not happen.
+
+
+Both ACE & DBaaS clusters can be of any vendors like AWS, Azure, Google Cloud etc. It can be an on-prem cluster too.

src/en/guides/get-started/images/architecture.png

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+---
+layout: 'guide'
+menu:
+  docs_menu:
+    identifier: guide-ace-requirements
+    name: ACE Requirements
+    parent: guide-start
+    weight: 14
+menu_name: docs_menu
+section_menu: guides
+---
+
+# Requirements to deploy ACE
+We will discuss the resources requirements. networking requirements & best practices for deploying your first ACE & DBaaS cluster. It is highly recommended to read the [architecture](https://appscode.com/docs/en/guides/get-started/architecture.html) doc first before continuing. 
+
+## Requirements for ACE Cluster
+
+### 1. Resources
+**Minimum**: Single node with 4 cpu, 16 GB ram, 100 GB disk attached. A k3s cluster will be deployed on that VM. And then the ui-components will be installed.
+
+**HA Deployment**: 3 worker nodes, each with 4 cpu, 16 GB ram, PVC support (3000 iops, 200 GB disk across multiple pvcs) and LB service support. The Kubernetes control plane should be also HA.
+
+### 2. Networking
+If you want to run in an air-gapped environments (disconnected from internet), You will have to make sure that all images are cached locally. You can use Harbor or jfrog artifactory for this. 
+
+We maintain a complete list of the [charts](https://github.com/appscode-cloud/installer/blob/master/catalog/copy-images.sh) & [images](https://github.com/appscode-cloud/installer/blob/master/catalog/ace.yaml).
+
+#### Connectivity
+These are the required connectivities to everything work correctly:
+- `DB pod to pod` communication using dns (k8s service discovery)
+- `operator to db-pods` for health checks
+- `db pods to kube-apiserver` for failover handling (update pod label when it becomes a primary replica)
+- `operator to kube-apiserver` for CRUD
+- `Backup pods to db pods` over network and on node level so they can access the shared disks.
+- `Backup pods to object storage` (s3 , minio etc.)
+
+#### Port Requirements
+1. 80  -  Auto redirects to https
+2. 443  -  Https Ingress port
+3. 4222  -  NATS.io port
+4. 4224  -  s3-proxy service port
+
+Here is a sample video on how you can setup ACE:
+<iframe width="560" height="315" src="https://www.youtube.com/embed/1diG8qq73f4?si=pisqA3gOrfO1wxlx" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
+
+## Requirements for DBaaS Cluster
+### 1. Resources
+Depends on how many and what size of databases users are running.
+
+Minimum: Kubernetes cluster with 3 worker nodes, each with 8- 16GB ram, PVC support (3000 iops, 200 GB disk across multiple pvcs) and LB service support.
+
+Note that, The largest node must be able to fit the largest DB Pod(in terms of CPU, memory).
+
+### 2. Networking
+Literally all the Networking requirements described for ACE are also applicable here, except the `Port Requiements` part.
+Only one additional requirement here is that the DBaaS cluster should be accessible from the management/ACE cluster.
+
+You now have an overall idea on the requirements. So, [Login](https://appscode.com/docs/en/guides/get-started/register-login.html) into your account & get going with our [installer](https://appscode.com/selfhost/). Happy ACE!