251 lines
3.7 KiB
Markdown
251 lines
3.7 KiB
Markdown
# High Availability Architecture
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This document outlines the **high availability design** for the application infrastructure.
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Goals:
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* Primary hosting in **Microsoft Azure**
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* Automatic failover to **on-premise infrastructure**
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* Minimal downtime
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* Disaster recovery backups through **CBM Technology** / **Rader Solutions**
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---
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# 1. Architecture Overview
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```mermaid
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flowchart TB
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A[Architecture Overview]
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A --> B[Primary Cloud Azure]
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A --> C[Secondary On Prem]
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A --> D[Tertiary CBM Backup]
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B --> B1[Azure Application Gateway]
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B --> B2[Main Application Server]
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B --> B3[Primary Database]
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B --> B4[External Access with IP Restrictions]
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C --> C1[Replica Application Server]
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C --> C2[Database Replica]
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C --> C3[File Storage Replica]
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C --> C4[Used During Internet Loss]
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D --> D1[Daily Snapshots of Azure Primary]
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D --> D2[Disaster Recovery Scenario]
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```
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---
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# 2. Architecture Flow Diagram
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```mermaid
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flowchart LR
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PC[User PC]
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FW[On Prem Firewall Reverse Proxy]
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VPN[Site to Site VPN]
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INT[Internet]
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AZGW[Azure Application Gateway]
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AZAPP[Azure Application Server]
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AZDB[(Primary Database Azure)]
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OPDB[(Replica Database On Prem)]
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OPAPP[On Prem Application Server]
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PC --> FW
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FW --> VPN
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VPN --> INT
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INT --> AZGW
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AZGW --> AZAPP
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AZAPP --> AZDB
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AZDB --> OPDB
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OPDB --> OPAPP
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FW --> OPAPP
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```
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Normal operation routes traffic to Azure.
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If the office internet fails, the firewall redirects users to the on-prem server.
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---
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# 3. DNS Connection
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```mermaid
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flowchart LR
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PC[User PC]
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GW[Gateway Firewall]
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DNS[app.avexmro.com]
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AZ[Azure Cloud Server]
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OP[On Prem Server]
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PC --> GW
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GW --> DNS
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DNS -->|WAN UP| AZ
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DNS -->|WAN DOWN| OP
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```
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Behavior:
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Normal operation
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```
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app.avexmro.com → Azure
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```
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Internet outage
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```
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app.avexmro.com → On Prem
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```
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WAN state detection is handled by the gateway firewall.
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---
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# 4. Database and File Replication
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```mermaid
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flowchart LR
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AZDB[(Azure Primary Database)]
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OPDB[(On Prem Replica Database)]
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AZFILES[Azure File Storage]
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OPFILES[On Prem File Storage]
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AZDB -->|Secure Replication| OPDB
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AZFILES -->|Continuous File Sync| OPFILES
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```
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Normal state
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```
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Azure → On Prem replication
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```
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Failover state
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```
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On Prem promoted to primary
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Replication paused
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```
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Recovery state
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```
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On Prem → Azure resync
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Azure resumes primary role
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```
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---
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# 5. Monitoring Layer
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```mermaid
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flowchart TB
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MON[Health Monitoring System]
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AZAPP[Azure Application Server]
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AZDB[Azure Database]
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OPAPP[On Prem Application Server]
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OPDB[On Prem Database]
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ALERT[Alerting and Failover Trigger]
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MON --> AZAPP
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MON --> AZDB
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MON --> OPAPP
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MON --> OPDB
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MON --> ALERT
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```
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Monitoring ensures:
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* replication health
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* server availability
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* automatic failover triggers
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Possible tools:
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* Azure Monitor
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* Zabbix
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* Uptime Kuma
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* Prometheus
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---
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# 6. Failover State Machine
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```mermaid
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flowchart TD
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A[Normal Operation Azure Primary]
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B[Internet Loss Detected]
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C[Local Failover Mode On Prem Primary]
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D[Internet Restored]
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E[Data Resynchronization]
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F[Return to Normal Azure Primary]
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A --> B
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B --> C
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C --> D
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D --> E
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E --> F
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```
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Failover sequence:
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1. Azure operates as primary
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2. Internet outage detected
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3. On-prem database promoted
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4. Office operates locally
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5. Internet restored
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6. Data resynchronizes to Azure
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7. Azure resumes primary role
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---
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# Reliability Model
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Expected behavior during failure scenarios:
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| Event | Result |
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| ---------------------- | -------------------------- |
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| Azure VM failure | Azure HA handles |
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| Azure maintenance | No downtime |
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| Office internet outage | Automatic on-prem failover |
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| Local server failure | Cloud still available |
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| Database corruption | Restore from CBM backup |
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| Company power outage | Service interruption |
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--- |