High Availability Architecture Guide

📋 Overview

🏛️ Architecture

🗄️ Databases

⚖️ Load Balancing

📊 Monitoring

💾 Storage

🎯 What is High Availability?

High Availability (HA) ensures your system remains operational even when components fail. It's achieved through redundancy, failover mechanisms, and distributed architecture.

🔄 Redundancy

Multiple instances of critical components across different zones

🚀 Auto-Failover

Automatic switching to backup systems when primary fails

📍 Multi-AZ Design

Distribution across multiple Availability Zones

🔍 Health Monitoring

Continuous monitoring and health checks

📈 HA Implementation Steps

Design for Failure
Assume every component will fail and plan accordingly

Implement Redundancy
Deploy multiple instances across different zones/regions

Set Up Monitoring
Implement health checks and alerting systems

Test Failover
Regularly test your disaster recovery procedures

🏛️ Complete HA Architecture

🌐 DNS Layer

Route 53
Health Checks & DNS Failover

⚖️ Load Balancer Layer

NGINX (AZ-1)
Primary LB

NGINX (AZ-2)
Backup LB

HAProxy
DB Proxy

🖥️ Application Layer

App Server 1
AZ-1

App Server 2
AZ-2

Worker Queue
Background Jobs

🗄️ Database Layer

PostgreSQL Primary
Writer

PostgreSQL Replica
Reader

Redis Cluster
Cache & Sessions

💾 Storage Layer

S3 Primary Region
Object Storage

S3 Backup Region
Cross-Region Replication

📊 Monitoring Layer

ELK Stack
Logging

Prometheus + Grafana
Metrics & Alerts

🎮 Simulate Architecture

Click to simulate different failure scenarios:

🗄️ Database High Availability

PostgreSQL HA with Patroni

Patroni manages PostgreSQL clusters with automatic failover using consensus algorithms.

                # Patroni Configuration
                bootstrap:
                dcs:
                ttl: 30
                loop_wait: 10
                retry_timeout: 30
                maximum_lag_on_failover: 1048576
                initdb:
                - encoding: UTF8
                - data-checksums
                pg_hba:
                - host replication replicator 127.0.0.1/32 md5
                - host all all 0.0.0.0/0 md5
            

📊 PostgreSQL HA Setup

etcd/Consul
Consensus Store

PostgreSQL Primary
Read/Write

PostgreSQL Standby
Read Only

HAProxy
Connection Routing

MongoDB Replica Set

MongoDB uses replica sets for automatic failover with a minimum of 3 nodes for election.

                // MongoDB Replica Set Configuration
                rs.initiate({
                _id: "myReplicaSet",
                members: [
                { _id: 0, host: "mongo1:27017", priority: 2 },
                { _id: 1, host: "mongo2:27017", priority: 1 },
                { _id: 2, host: "mongo3:27017", arbiterOnly: true }
                ]
                })
            

Redis High Availability

Redis Sentinel provides monitoring and automatic failover for Redis instances.

                # Redis Sentinel Configuration
                sentinel monitor mymaster 192.168.1.100 6379 2
                sentinel down-after-milliseconds mymaster 5000
                sentinel failover-timeout mymaster 10000
                sentinel parallel-syncs mymaster 1
            

⚖️ Load Balancing & Traffic Management

🌐 Traffic Flow

Route 53
DNS Load Balancing

Application Load Balancer
Layer 7 (HTTP/HTTPS)

Network Load Balancer
Layer 4 (TCP/UDP)

NGINX Instance 1
AZ-1

NGINX Instance 2
AZ-2

NGINX Configuration for HA

                upstream backend {
                server app1.example.com:8080 max_fails=3 fail_timeout=30s;
                server app2.example.com:8080 max_fails=3 fail_timeout=30s;
                server app3.example.com:8080 backup;
                }

                server {
                listen 80;
                location / {
                proxy_pass http://backend;
                proxy_set_header Host $host;
                proxy_set_header X-Real-IP $remote_addr;

                # Health check
                proxy_connect_timeout 5s;
                proxy_send_timeout 10s;
                proxy_read_timeout 10s;
                }
                }
            

HAProxy Configuration

                backend postgres_backend
                balance roundrobin
                option httpchk GET /health
                server pg1 10.0.1.100:5432 check
                server pg2 10.0.1.101:5432 check backup

                frontend postgres_frontend
                bind *:5432
                default_backend postgres_backend
            

Load Balancer Type	Use Case	Features	Failover Time
Route 53	DNS-based routing	Health checks, Geo-routing	30-60 seconds
Application LB	HTTP/HTTPS applications	Path-based routing, SSL termination	~10 seconds
Network LB	TCP/UDP traffic	Ultra-low latency, static IP	~5 seconds
NGINX	Reverse proxy	High performance, caching	Immediate
HAProxy	Database connections	Advanced health checks	Immediate

📊 Monitoring & Observability

📈 Metrics Collection

Prometheus scrapes metrics from all components

📋 Log Aggregation

ELK Stack centralizes logs from all services

🚨 Alerting

Grafana alerts on threshold breaches

🔍 Distributed Tracing

Track requests across microservices

📊 Monitoring Stack

Grafana
Visualization & Alerts

Prometheus
Metrics Storage

Elasticsearch
Log Storage

Node Exporter
System Metrics

Logstash
Log Processing

Filebeat
Log Shipping

Key Monitoring Metrics

System Metrics: CPU, Memory, Disk I/O, Network
Application Metrics: Response time, Error rate, Throughput
Database Metrics: Connection pool, Query performance, Replication lag
Infrastructure Metrics: Load balancer health, Auto-scaling events

            # Prometheus Alert Rules
            groups:
            - name: database
            rules:
            - alert: PostgreSQLDown
            expr: up{job="postgresql"} == 0
            for: 1m
            labels:
            severity: critical
            annotations:
            summary: "PostgreSQL instance is down"

            - alert: HighDatabaseConnections
            expr: postgresql_stat_database_numbackends > 80
            for: 5m
            labels:
            severity: warning
            annotations:
            summary: "High number of database connections"
        

💾 Storage & Data Management

🗄️ Storage Architecture

S3 Primary
us-east-1

S3 Replica
us-west-2

EBS Volumes
Database Storage

EFS
Shared File System

Backup Jobs
Automated Backups

Glacier
Long-term Archive

Storage Type	Use Case	Durability	Availability
S3 Standard	Frequently accessed data	99.999999999%	99.99%
S3 Cross-Region Replication	Disaster recovery	99.999999999%	99.99%
EBS with Snapshots	Database storage	99.999%	99.99%
EFS	Shared file storage	99.999999999%	99.99%

Backup Strategy

Daily Database Backups
Automated backups with point-in-time recovery

File System Snapshots
EBS snapshots for consistent backups

Cross-Region Replication
Replicate critical data to multiple regions

Archive to Glacier
Long-term storage for compliance and cost optimization

            # S3 Cross-Region Replication Configuration
            {
            "Role": "arn:aws:iam::account:role/replication-role",
            "Rules": [
            {
            "ID": "ReplicateEverything",
            "Status": "Enabled",
            "Prefix": "",
            "Destination": {
            "Bucket": "arn:aws:s3:::backup-bucket-west",
            "StorageClass": "STANDARD_IA"
            }
            }
            ]
            }
        

🏗️ High Availability Architecture Guide