Rolling deployment vs kill switch: Choosing a deployment strategy

Rolling deployment

Rolling deployment is a strategy where updates are gradually rolled out across instances of an application. Instead of updating all servers simultaneously, the deployment proceeds one server or batch at a time. This approach ensures continuous availability, as only a portion of the infrastructure is offline during the update process, allowing remaining servers to handle ongoing traffic.

This method significantly reduces downtime risks and allows for incremental verification of the deployment’s success. If issues are detected during the rollout, the deployment can be paused while affecting only a subset of users. Rolling deployments are particularly valuable in environments where high availability is critical and where complete service interruption is unacceptable.

Kill switch

A kill switch is a deployment strategy focusing on risk mitigation through rapid reversion capabilities. It provides an emergency mechanism to quickly disable newly deployed features or rollback an entire deployment when critical issues are detected in production. Kill switches act as a safety net, allowing teams to respond immediately to unexpected problems without complex remediation procedures.

When activated, a kill switch typically reverts the system to a previous stable state or disables specific functionality causing issues. This approach is particularly valuable in high-stakes environments where service reliability is paramount. Kill switches emphasize the ability to recover quickly from failures rather than preventing them entirely, acknowledging that not all issues can be caught in testing environments.

Comparing rolling deployment and kill switch

Implementation complexity

• Rolling Deployment: Requires orchestration tools and careful capacity planning to maintain service availability during transitions.

• Kill Switch: Relatively simpler to implement as it focuses on binary on/off functionality rather than gradual transition logic.

Recovery speed

• Rolling Deployment: Recovery from issues involves continuing the rollout of the previous version, which may take considerable time.

• Kill Switch: Offers near-immediate recovery as problematic features can be disabled instantly system-wide.

Traffic management

• Rolling Deployment: Necessitates load balancer configuration to route traffic appropriately during the phased deployment.

• Kill Switch: Generally doesn’t require special traffic routing as it operates by enabling/disabling functionality rather than changing infrastructure.

Risk profile

• Rolling Deployment: Distributes risk across time, limiting impact to subsets of users during the transition period.

• Kill Switch: Accepts full deployment risk but provides a quick escape mechanism when issues arise.

Resource utilization

• Rolling Deployment: Requires additional resources during transition as both old and new versions run simultaneously.

• Kill Switch: Typically has minimal additional resource requirements beyond normal deployment needs.

Feature flags with rolling deployments

When implementing feature flags with rolling deployments, teams gain an additional layer of control over the release process. Feature flags can be deployed across the infrastructure in a disabled state during the rolling update, ensuring code is in place but not active. Once the deployment is complete and verified across all instances, the feature flag can be gradually enabled for increasing percentages of users, creating a “deployment within a deployment” approach that further mitigates risk.

This combination is particularly powerful because it separates code deployment from feature activation. If issues arise during the flag enablement phase, teams can immediately disable the feature without needing to roll back code. This approach also allows for targeted testing by enabling the feature for internal users or a small percentage of customers while the rolling deployment is still in progress, providing early feedback without widespread exposure.

Feature flags with kill switches

Feature flags essentially function as granular kill switches themselves, making them natural companions to a kill switch deployment strategy. While a traditional kill switch might revert an entire deployment, feature flags allow for more surgical control by enabling teams to disable specific problematic features while leaving the rest of the deployment intact. This reduces the blast radius of issues and allows teams to address problems with minimal disruption to uninvolved functionality.

In critical systems, feature flags can be configured with automated kill switch behavior, where monitoring systems automatically disable a feature flag if predefined error thresholds are exceeded. This creates a self-healing aspect to deployments that doesn’t require human intervention for initial response. Teams can then investigate issues while users experience the stable, previous behavior, and later re-enable the feature once fixes are implemented and verified, all without additional deployments or full system rollbacks.

In the realm of software deployment strategies, both Rolling Deployments and Kill Switches offer distinct advantages and limitations. Rolling Deployments gradually replace instances of the previous version with the new one, allowing for a controlled transition that minimizes downtime and enables verification of the new version with a subset of users before full deployment. This approach provides the ability to catch issues early while maintaining system availability, making it ideal for environments where continuous service is critical. However, Rolling Deployments can be time-consuming, especially for large-scale applications, and may introduce temporary inconsistencies during the transition period when different versions coexist. Additionally, they require more complex infrastructure and monitoring to manage the gradual rollout effectively.

Kill Switches, on the other hand, offer immediate response capabilities in crisis situations by allowing teams to instantly disable specific features or revert to previous versions. This approach shines in scenarios requiring rapid reaction to critical bugs or security vulnerabilities, providing a safety net that can prevent widespread negative impacts. Organizations should implement Kill Switches when deploying high-risk features or in systems where failures could have significant consequences. The main drawbacks include the possibility of creating abrupt user experience disruptions and potentially introducing their own bugs if not thoroughly tested. While Rolling Deployments are better suited for planned, gradual improvements in stable environments, Kill Switches are essential emergency mechanisms that should complement other deployment strategies rather than serve as the primary approach to software updates.

Frequently asked questions

What is a rolling deployment?

Rolling deployment is a strategy where updates are gradually rolled out across instances of an application, one server or batch at a time, rather than updating all servers simultaneously. This approach ensures continuous availability because only a portion of the infrastructure is offline during updates, allowing remaining servers to handle ongoing traffic. Rolling deployments reduce downtime risks and allow for incremental verification of the deployment’s success. If issues are detected during rollout, the deployment can be paused while affecting only a subset of users.

What is a kill switch?

A kill switch is a deployment strategy focusing on risk mitigation through rapid reversion capabilities. It provides an emergency mechanism to quickly disable newly deployed features or rollback an entire deployment when critical issues are detected in production. When activated, a kill switch typically reverts the system to a previous stable state or disables specific functionality causing issues. This approach emphasizes the ability to recover quickly from failures rather than preventing them entirely.

How do rolling deployments and kill switches compare in terms of implementation complexity?

Rolling deployments require orchestration tools and careful capacity planning to maintain service availability during transitions, making them more complex to implement. Kill switches are relatively simpler to implement as they focus on binary on/off functionality rather than gradual transition logic.

How do recovery speeds differ between rolling deployments and kill switches?

With rolling deployments, recovery from issues involves continuing the rollout of the previous version, which may take considerable time. Kill switches offer near-immediate recovery as problematic features can be disabled instantly system-wide.

How can feature flags enhance rolling deployments?

When implementing feature flags with rolling deployments, teams gain an additional layer of control over the release process. Feature flags can be deployed across the infrastructure in a disabled state during the rolling update, ensuring code is in place but not active. Once the deployment is complete and verified across all instances, the feature flag can be gradually enabled for increasing percentages of users. This combination separates code deployment from feature activation, allowing teams to disable features without rolling back code if issues arise.

How do feature flags work with kill switches?

Feature flags function as granular kill switches themselves, making them natural companions to a kill switch strategy. While a traditional kill switch might revert an entire deployment, feature flags allow for more surgical control by enabling teams to disable specific problematic features while leaving the rest of the deployment intact. In critical systems, feature flags can be configured with automated kill switch behavior, where monitoring systems automatically disable a feature flag if predefined error thresholds are exceeded.