Pilot Light Disaster Recovery (DR) Strategy | Deep Dive.

A deep-dive into Pilot Light Disaster-Recovery (DR) Strategy.

 Scope:

•        Architecture,
•        Components,
•        Pros/Cons,
•        Implementation patterns (AWS-focused but cloud-agnostic principles),
•        Compare-and-Contrast with other DR models.

Breakdown:

•        What “Pilot Light” Means,
•        Pilot Light Architecture Components,
•        Failover Process in Pilot Light,
•        When to Use Pilot Light,
•        Comparison  of Pilot Light With Other DR Strategies,
•        Key AWS Pilot Light Reference Architecture,
•        Cost Optimization Strategies for Pilot Light,
•        Testing a Pilot Light Strategy,
•        Pros and Cons of Pilot Light,
•        Final thoughts.

Intro:

•        Pilot Light DR strategy is a middle-ground between Backup & Restore and Warm Standby, that gives twtech  near-real-time data replication with minimal infrastructure running in the DR region.
•        Pilot Light DR strategy aims to keep the core of twtech system always “lit” (i.e., minimal critical services running), while everything else is launched during a failover.

 1. What “Pilot Light” Means

Think of aviation pilot lights—a small continuous flame that can ignite the full engine quickly.

In DR terms:

• A minimal version of twtech environment is always running in the DR region, consisting of the critical components needed to start its full application.

This includes:

•         Databases or core data storage (replicated & hot)
•         Critical IAM, networking, and security foundations
•         Possibly minimal compute nodes (images or small instances for core services)
•         Infrastructure code (IaC) ready to scale up the rest on failover

 2. Pilot Light Architecture Components

Core Components that MUST be running: These are twtech “always-on” elements in DR:

 1. Database or Data Layer (Hot Replication)

•         Cross-Region Database Replication
•         E.g.,
•    AWS RDS Cross-Region Read Replica
•    DynamoDB Global Tables
•    S3 Cross-Region Replication (CRR)
•    Kafka/MSK replication
•         Goal: Data is nearly up-to-date and ready to become primary.

 2. Minimal Compute Footprint

Not full production load—just critical infrastructure:

•         AMIs or machine images built & available in the DR region
•         Minimal EC2 or container cluster control planes
•    (e.g., ECS cluster created but no tasks running)
•         Lambda code deployed but not invoked
•         Container images replicated to DR region (ECR replication)

 3. Networking + Security Baseline

Pre-created resources to prevent delays:

•         VPCs, subnets, route tables
•         Security Groups, NACLs
•         Load balancers (either pre-created or deploy-on-failover)
•         DNS, ACM certificates in DR

 4. Infrastructure as Code (IaC)

Essential for rapid scaling on failover:

•         Terraform, CloudFormation, Pulumi, CDK
•         DR deployments automated and tested

 5. Failover Orchestration

Automatic or manual runbooks that:

•         Promote the DR database (read replica → primary)
•         Deploy & scale compute (ASGs, ECS tasks, EKS nodes)
•         Swap DNS (immediate or controlled)
•         Validate health checks and routing

Often implemented through:

•         Lambda + Step Functions
•         SSM Automation
•         EventBridge
•         Third-party DR orchestration tools (e.g., CloudEndure, Zerto)

 3. Failover Process in Pilot Light

Failover Steps

1.     Detect disaster (manual or monitored event)

2.     Promote databases in DR region

3.     Spin up application servers

•    Auto Scaling Groups scale from 0 → desired capacity
•    Launch ECS tasks / EKS deployments

4.     Switch DNS to DR resources

5.     Validate application health

6.     Full traffic routed to DR

RTO (Recovery Time Objective): ~30 minutes to a few hours

• Depending on how fast compute resources are deployed and data is promoted.

RPO (Recovery Point Objective): Seconds to minutes

• Because data is replicated continuously (asynchronous or synchronous).

 4. When to Use Pilot Light

Pilot Light works best when:

•         twtech needs better RTO than “Backup and Restore”
•         twtech wants lower cost than “Warm Standby”
•         twtech application can handle some ramp-up time
•         twtech compute layer can be created quickly from IaC
•         twtech data layer is the most critical part of recovery

Good fit for:

•         E-commerce catalogs
•         SaaS platforms
•         Internal enterprise line-of-business apps
•         Microservices with stateless compute

Not ideal when:

•         Mission-critical real-time systems require instant failover
•         Compliance mandates extremely low RTO (e.g., < 5 min)

 5. Comparison of Pilot Light With Other DR Strategies

DR Model	RTO	RPO	Cost	Notes
Backup & Restore	Hours–days	Hours	💲 Low	Data stored only; no infra running
Pilot Light	~30 min–hours	Seconds–minutes	💲💲 Medium	Core infra is live; scale on failover
Warm Standby	Minutes	<1 min	💲💲💲 Higher	Partially scaled environment always running
Multi-Site/Hot-Hot	Seconds	Zero	💲💲💲💲 Highest	Fully active in multiple regions

NB:

Pilot Light is the sweet spot for balancing performance and cost.

 6. Key AWS Pilot Light Reference Architecture (Sample)

Always Running in DR

•         RDS Read Replica (cross-region)
•         DynamoDB Global Tables
•         S3 CRR for assets/logs
•         VPC baseline:
•    VPC, subnets, route tables
•    Nat Gateway (optionally)
•         ECR cross-region replication
•         IAM roles, KMS keys

Stopped or Minimal Resources in DR

•         EC2 Auto Scaling Groups (0 desired capacity)
•         ECS/EKS clusters with no running tasks
•         Load balancers (optional pre-created)
•         CloudFront distribution pointing to failover origin
•         Lambda functions with reserved concurrency = 0

Failover Tooling

•         Route53 failover routing
•         SSM Automation documents
•         Step Functions to orchestrate:
•    Scale out compute
•    Promote RDS to primary
•    Enable ALBs / Target Groups
•    Update Route53 records

7. Cost Optimization Strategies for Pilot Light

•         Use smaller database replicas (if performance allows)
•         Scale-to-zero compute
•         ECR replication only for required images
•         DR region uses lower-cost instance families on failover
•         Spot instances for non-critical workloads during recovery
•         Use automation to delete DR infra after failback

 8. Testing a Pilot Light Strategy

• Frequency: Quarterly at minimum
• If compliance requires: Monthly or bimonthly

Tests usually include:

•         Activate DR region
•         Validate app functionality
•         Validate RDS promotion
•         Validate CI/CD pipeline can deploy to DR
•         Validate DNS failover
•         Run rollback or failback process

Automated testing can greatly reduce operational burden.

 9. Pros and Cons of Pilot Light

✅ Pros

•         Significantly reduced cost vs Hot Standby
•         Near real-time data replication
•         Flexible & scalable via Infrastructure as Code
•         Works well with microservices & serverless
•         Faster than Backup & Restore

❌ Cons

•         Not immediate failover (compute still has to scale up)
•         Requires ongoing testing to ensure reliability
•         Risk of configuration-drift if IaC not 100% reliable
•         Failover orchestration can be complex

Final thoughts

Pilot Light is a cost-effective, highly automated, moderate-RTO DR strategy where:

•         twtech data is hot
•         twtech critical infrastructure is minimal but ready
•         The application tier is deployed only during disaster

twtech Recommendation:

Pilot Light disaster-recovery (DR) strategy is ideal for organizations that need better resilience without the cost of full multi-site.