Single‑Region, Single‑Availability Zone (AZ) Resiliency Overview
A Single‑Region, Single‑Availability Zone (AZ) deployment represents the most basic cloud architecture model. While simple and cost‑effective, it offers minimal resiliency and exposes workloads to significant infrastructure‑level risks. This architecture is often seen in:
- Early‑stage or proof‑of‑concept environments
- Cost‑optimized setups
- Legacy applications not yet modernized
- Development or testing workloads
Despite its simplicity, understanding its limitations and best‑practice safeguards is crucial—especially for database‑driven systems.
What Is an Availability Zone (AZ)?
An Availability Zone is an isolated, physically separate data center within a cloud region (AWS, Azure, GCP). Each AZ typically has:
- Independent power supply
- Isolated networking
- Separate cooling and physical security
In a Single‑AZ deployment:
- All compute, storage, network, and database resources reside within one data center.
- No cross‑AZ failover exists.
- A failure of that AZ directly impacts the entire workload.
Resiliency Characteristics in a Single‑Region, Single‑AZ Setup
What You Can Protect Against (Within the AZ)
A Single‑AZ design can mitigate failures limited to the infrastructure within that AZ:
- Virtual machine or instance failures
- Application‑level crashes
- Software defects
- Local disk issues
- Process‑level outages
Typical mechanisms include:
- VM/Pod auto‑restart
- Platform‑provided auto‑healing
- Load balancing across multiple instances inside the AZ
- Database failover within the same AZ
- Backup and restore procedures
What You Cannot Protect Against
A Single‑AZ setup cannot safeguard against data‑center‑level events, such as:
- Complete AZ outage
- Power disruption
- Networking isolation
- Fire, flooding, or physical damage
- Regional outage (if the entire region is impacted)
If the AZ becomes unavailable, the entire workload becomes unavailable.
No automated recovery is possible without manual redeployment.
Best Practices for Improving Resiliency Within a Single AZ
1. Intra‑AZ Redundancy
- Multiple compute nodes deployed in the same AZ
- Load balancer distributing traffic among nodes
- Managed database with synchronous replication to an in‑AZ standby
2. Automated Recovery
- Use of Auto‑Scaling Groups (ASG) or equivalent orchestration platforms
- Health‑based instance replacement
- Application‑level crash recovery mechanisms
3. Data Durability
Even in Single‑AZ deployments, data durability must extend beyond that AZ:
- Scheduled backups stored in multi‑AZ or multi‑region storage (S3/Blob/GCS)
- Point‑in‑time recovery (PITR) where supported
- Protection against accidental deletion or corruption
4. Monitoring & Alerting
- Infrastructure and application health checks
- Centralized logging and correlation
- Alerting on metrics such as CPU, disk, latency, and database health
5. Incident Response & Runbooks
- Documented steps to restore from backup
- Procedure to redeploy stack to a new AZ or region if required
- Defined responsibilities and escalation policies
Key Risks to Communicate to Stakeholders
A Single‑AZ architecture has inherent business and technical risks:
- No fault tolerance for AZ‑level failures
- No disaster recovery (DR) capability
- Increased RTO (Recovery Time Objective)
- Increased RPO (Recovery Point Objective)
- Higher likelihood of prolonged downtime during outages
Suitable only for:
- Development and testing environments
- Low‑criticality workloads
- Cost‑sensitive deployments
- Legacy systems not yet refactored
Not suitable for:
- Mission‑critical applications
- Customer‑facing platforms requiring high availability
- Systems requiring compliance‑driven uptime guarantees
As a Database Architect: Key Responsibilities in Single‑AZ Designs
Even within a restricted resiliency model, you must ensure database stability, recoverability, and data integrity.
Minimum DB Resiliency Expectations
- Synchronous in‑AZ replica (where supported)
- Automated database failover within the AZ
- Continuous backups stored in cross‑AZ or multi‑region storage
- Point‑in‑time recovery (PITR) configuration
- Automated recovery workflows (bootstrapping, failover scripts, restoration steps)
- Regular testing of backup and restore procedures
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