AWS Pilot Light vs. Warm Standby: Disaster Recovery Compared
Published on · Updated on
Revised Pilot Light and Warm Standby definitions, recovery objectives, and regional disaster recovery guidance.
AWS Pilot Light and Warm Standby are two active-passive disaster recovery (DR) patterns for running a workload in a recovery Region. Both keep data and parts of the application environment available there, but they differ in how much of the application is already running and how much work remains before it can serve production traffic.
That difference affects recovery effort and ongoing cost, but neither pattern promises a fixed recovery time or amount of data loss. Choose against the recovery time objective (RTO) and recovery point objective (RPO) set for the workload, then test the complete recovery procedure.
Pilot Light vs. Warm Standby at a glance
| Dimension | Pilot Light | Warm Standby |
|---|---|---|
| Recovery environment | Core infrastructure and replicated data are prepared; application compute may be stopped or deployed during recovery. | A functional, reduced-capacity copy of the workload is already running. |
| Work before serving traffic | Start or deploy missing components, scale capacity, validate dependencies, then route traffic. | Validate readiness, route traffic, and scale up as needed. |
| RTO and RPO | Often needs more recovery steps than Warm Standby. Actual RTO and RPO depend on the workload, data protection, and runbook. | Can reduce activation time because more of the stack is running. Data recovery point still depends on replication and backup behavior. |
| Cost profile | Often has lower ongoing compute cost because fewer application resources run in standby. | Usually costs more to operate because a reduced-capacity application stack stays active. |
| Good fit when | The workload can tolerate activation work during recovery and the team can automate and test it. | The workload needs a shorter recovery path and the business can fund and operate a live standby stack. |
These are design tendencies, not service guarantees. Actual costs depend on the services, data volume, replication, backup retention, and standby capacity you choose. AWS describes both patterns as workload-level strategies; its disaster recovery guidance explains the differences in more detail.
Set recovery objectives before choosing
RTO is the maximum acceptable delay between a service interruption and restoration. RPO is the maximum acceptable time since the latest recoverable data point, which defines how much recent data the business can tolerate losing. These objectives belong to the business and should be defined for each workload. AWS explains the relationship in its DR objectives guidance.
State the failure you need to recover from as well. Multi-AZ design in one Region can address some Availability Zone failures; a second Region is a separate recovery boundary for regional failures. Neither Pilot Light nor Warm Standby alone protects against every cause of outage, such as a destructive deployment, compromised credentials, or corrupted data. Keep recoverable backups and point-in-time recovery where those events matter: replication can copy a bad change to the recovery Region.
How Pilot Light works
In a Pilot Light design, data is replicated to the recovery Region and the core infrastructure needed to rebuild the workload is prepared there. Resources needed for replication and data access remain available. Application compute may be stopped or not deployed until recovery; infrastructure as code, machine images, application artifacts, and configuration let the team create or start the missing pieces consistently.
During recovery, the team or automation starts or deploys application components, scales the environment, checks dependencies and data, and redirects traffic after the recovery site is ready. This pattern can reduce idle compute compared with keeping a live application stack in the recovery Region, while preserving more prepared infrastructure than a backup-and-restore design. It still requires a tested sequence and enough regional capacity and service quotas for the recovered workload.
Pilot Light tradeoffs
- Lower standby compute is possible: fewer application resources run continuously, though replicated data, backups, and other always-on services still have costs.
- More actions remain during recovery: starting or deploying services, promoting data stores, and scaling capacity add steps and dependencies to the runbook.
- Automation matters: keep the recovery environment and application configuration aligned with production, and rehearse changes that could affect deployment or permissions.
How Warm Standby works
Warm Standby keeps a reduced-capacity but functional copy of the workload running in another Region. It should be able to process traffic at its current capacity, rather than waiting for application compute to be deployed. When a disaster is declared, the recovery procedure validates the environment, directs traffic to it, and scales resources to meet the production load as required.
Warm Standby can shorten the work before service resumes because the application stack is already running. Recovery can still depend on traffic routing, database promotion, scaling operations, regional quotas, and application checks. Provisioning enough resources ahead of time may reduce scaling dependence, but it also increases ongoing cost. The appropriate standby size depends on how much degraded capacity the business can accept while the recovered workload scales up.
Warm Standby tradeoffs
- Fewer activation steps: a live, reduced-capacity environment avoids some deployment and startup steps.
- Standby resources cost more to operate: the recovery Region continuously runs more of the workload than a Pilot Light design.
- Data recovery is a separate concern: a running application does not guarantee a current recovery point or protect against corrupted data. Plan replication and backups for the data service you use.
Choose the pattern for the workload
Use these questions to make the tradeoff concrete:
- What RTO and RPO has the business approved? Treat them as acceptance targets, not assumptions inferred from a named AWS pattern.
- What must be ready before users can work? Map application components, data stores, identity and access, secrets, encryption keys, networking, dependencies, and traffic routing in the recovery Region.
- What can the recovery site handle before it is scaled? For Warm Standby, specify which customer operations can run at reduced capacity. For Pilot Light, identify every step required before any production request can succeed.
- Can the team operate the recovery path? Include people, approvals, runbooks, automation, quotas, monitoring, and failback. A pattern whose steps cannot be completed within the RTO is not a fit, whatever its diagram suggests.
- What protection is needed from data loss or corruption? Define replication behavior and lag, and keep backups or point-in-time recovery for recovery cases replication cannot address.
AWS's Well-Architected disaster recovery guidance recommends selecting a strategy against each workload's recovery requirements and ensuring the recovery Region has the resources needed. If regional failover, dependencies, and data consistency are part of a broader resilience design, see our guide to cross-service resilience and disaster recovery.
Test recovery, not just infrastructure
A running instance, completed replication, or successful backup job does not prove that the user-facing service can recover. Run the recovery procedure in an isolated environment and include the steps that count toward your RTO: detection or declaration, data promotion or restore, application startup, dependency checks, traffic changes, and a representative health check. Record the recovery-point timestamp to assess RPO and the time when the defined service check passes to assess RTO. If a test omits part of the real procedure, report the measured segment separately.
Test failback as well as failover. Before routing service back, verify the original Region, reconcile data, restore the intended replication direction, and confirm the application can safely receive traffic. For a detailed test plan covering AWS Elastic Disaster Recovery drills, AWS Backup restore tests, application checks, and cleanup, read our guide to testing AWS disaster recovery.
Frequently asked questions
Is Warm Standby always faster than Pilot Light?
Warm Standby keeps a functional reduced-capacity workload running, so it commonly has fewer activation steps. The actual recovery time still depends on data promotion, traffic routing, scaling, dependencies, and the validation process. Measure it in a recovery exercise instead of treating the pattern name as an RTO guarantee.
Does Warm Standby prevent data loss?
No. Its application environment is ready to run, but RPO depends on the selected data services, their replication behavior, and backup or point-in-time recovery. Replication may lag and may reproduce unwanted writes or deletions, so include a recovery point that can address data corruption where needed.
Which pattern costs less?
Pilot Light often has lower ongoing compute costs because less application capacity runs in standby. Warm Standby keeps more resources active and generally costs more to run. Compare the full design, including data replication, backups, network transfer, recovery tests, and the standby capacity required to meet your objectives.