Add HA_ARCHITECTURE.md

HA_ARCHITECTURE.md

@@ -0,0 +1,274 @@
+# High Availability System Architecture
+
+## Overview
+
+This document describes the architecture for the **high availability deployment of the application system**.
+
+The system is designed to maintain service availability during infrastructure or network failures by using **cloud infrastructure as the primary environment** and **on-premises infrastructure as a failover system**.
+
+The design prioritizes:
+
+* minimal downtime
+* automatic failover during internet outages
+* data replication between cloud and local systems
+* disaster recovery backups through CBM Technology
+
+The architecture combines **cloud reliability with local failover capability** to maintain service continuity.
+
+---
+
+# Architecture Overview
+
+```mermaid
+flowchart TB
+
+USER[Users]
+
+INT[Internet]
+
+CLOUD[Cloud Application Server]
+
+CLOUDDB[(Primary Database)]
+
+ONPREM[On Prem Application Server]
+
+ONDB[(Replica Database)]
+
+BACKUP[CBM Backup System]
+
+USER --> INT
+INT --> CLOUD
+CLOUD --> CLOUDDB
+
+CLOUDDB --> ONDB
+ONDB --> ONPREM
+
+CLOUD --> BACKUP
+CLOUDDB --> BACKUP
+```
+
+---
+
+# System Access
+
+Users normally access the system through the internet using the **primary cloud deployment**.
+
+Example:
+
+```
+https://app.companydomain.com
+```
+
+Traffic flow during normal operation:
+
+```mermaid
+flowchart LR
+
+USER[User Device]
+
+INT[Internet]
+
+APP[Cloud Application Server]
+
+DB[(Primary Database)]
+
+USER --> INT
+INT --> APP
+APP --> DB
+```
+
+---
+
+# Failover Operation
+
+If the office internet connection fails, internal users are redirected to the **local on-premises server**.
+
+```mermaid
+flowchart LR
+
+USER[User Device]
+
+LAN[Company Network]
+
+ONAPP[On Prem Application Server]
+
+ONDB[(Local Database)]
+
+USER --> LAN
+LAN --> ONAPP
+ONAPP --> ONDB
+```
+
+This allows employees to continue using the system locally until internet connectivity is restored.
+
+---
+
+# Infrastructure Components
+
+## Cloud Application Server
+
+The primary system runs in the **cloud environment**.
+
+Responsibilities include:
+
+* hosting the web application
+* processing user requests
+* managing application services
+* connecting to the primary database
+
+The cloud server is the **default production environment**.
+
+---
+
+## On-Prem Application Server
+
+The on-prem server provides **local failover capability**.
+
+Responsibilities include:
+
+* maintaining a replica of the application
+* providing access during internet outages
+* hosting the replicated database
+
+This server remains **standby during normal operations**.
+
+---
+
+## Primary Database
+
+The primary database resides in the cloud environment and stores all operational data.
+
+Examples include:
+
+* inventory records
+* user data
+* configuration settings
+* system transactions
+
+The cloud database acts as the **authoritative source of data**.
+
+---
+
+## Replica Database
+
+A replica database runs on the on-prem server.
+
+The replica receives continuous updates from the cloud database to ensure the local system stays synchronized.
+
+---
+
+# Database Replication
+
+Database replication ensures the on-prem system has an up-to-date copy of the cloud database.
+
+```mermaid
+flowchart LR
+
+CLOUDDB[(Cloud Primary Database)]
+
+ONDB[(On Prem Replica Database)]
+
+CLOUDDB --> ONDB
+```
+
+Normal operation:
+
+```
+Cloud → On Prem replication
+```
+
+Failover mode:
+
+```
+On Prem database promoted to primary
+Replication temporarily paused
+```
+
+Recovery mode:
+
+```
+On Prem → Cloud resynchronization
+Cloud resumes primary role
+```
+
+---
+
+# Backup System
+
+Backups are managed by CBM Technology.
+
+```mermaid
+flowchart LR
+
+APP[Cloud Application Server]
+
+DB[(Primary Database)]
+
+CBM[CBM Backup Storage]
+
+APP --> CBM
+DB --> CBM
+```
+
+Backups typically include:
+
+* database backups
+* server snapshots
+* file storage backups
+
+---
+
+# Backup Schedule
+
+Typical configuration:
+
+| Backup Type         | Frequency             |
+| ------------------- | --------------------- |
+| Database Backup     | Daily                 |
+| Server Snapshot     | Daily                 |
+| File Storage Backup | Daily                 |
+| Retention Period    | Defined by CBM policy |
+
+Backups are stored **offsite** to protect against data loss.
+
+---
+
+# Disaster Recovery
+
+If the primary cloud system fails:
+
+1. The on-prem server can be promoted to the primary system.
+2. Internal users connect to the local server.
+3. Operations continue locally until the cloud environment is restored.
+
+If both environments fail or data corruption occurs:
+
+1. CBM Technology restores the most recent backup.
+2. The system infrastructure is rebuilt if required.
+3. Services are returned to normal operation.
+
+---
+
+# Expected System Behavior
+
+| Event                  | Result                                   |
+| ---------------------- | ---------------------------------------- |
+| Cloud server failure   | Failover to on-prem server               |
+| Office internet outage | Internal users connect to on-prem server |
+| Local server failure   | Cloud system remains available           |
+| Database corruption    | Restore from CBM backup                  |
+| Company power outage   | System temporarily unavailable           |
+
+---
+
+# Potential Future Improvements
+
+Additional improvements may include:
+
+* cloud load balancing
+* multiple application servers
+* automated failover monitoring
+* geographic redundancy
+* network redundancy inside the office
+
+These improvements would further increase system reliability and reduce recovery times.