Professional Cloud DevOps Engineer
When an incident occurs, you can reduce its impact by carefully managing how user traffic reaches your services. Draining traffic means gradually stopping new requests from going to a specific instance or version of your service while letting existing connections finish their work. This is often done before shutting down an unhealthy or outdated server to prevent users from experiencing errors. Redirecting traffic involves shifting requests away from a problematic component to a healthy one, often using a load balancer or a global traffic manager. The decision to drain or redirect depends on whether you need to gracefully stop a single resource or immediately reroute all users to a backup system.
A common way to mitigate an incident's impact is to add more resources to handle the increased load or to replace failed components. This can be done manually or automatically through autoscaling. Autoscaling policies watch metrics like CPU usage or request latency; when a threshold is crossed, the system automatically adds more virtual machine instances or container pods to the pool. Adding capacity helps maintain performance and availability during a traffic surge or partial failure. However, it's important to understand that scaling takes time—new instances must be provisioned, start up, and pass health checks before they can receive traffic—so planning for this delay is part of incident response.
If a recent change caused an incident, rolling back to a previous, known-good version of your application or infrastructure is a key mitigation tactic. A rollback typically involves redeploying an earlier, stable configuration. In a continuous deployment pipeline, this can often be triggered automatically if health checks fail after a new release. The strategy depends on your deployment method: for containerized applications, you might roll back to a previous image version in your registry; for infrastructure as code, you revert to a prior commit in your configuration repository. A successful rollback quickly restores service, but it requires that previous versions are kept available and tested, and it may mean temporarily losing the features or fixes from the failed update.
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Draining traffic gradually stops new requests from going to a specific instance while allowing existing connections to finish their work, whereas redirecting traffic shifts requests away from a problematic component to a healthy backup using a load balancer or global traffic manager. Draining is typically performed before shutting down an unhealthy or outdated server, while redirecting is used when traffic must be rerouted immediately.
When autoscaling adds capacity, responders must account for the delay required for new virtual machine instances or container pods to be provisioned, start up, and pass health checks before receiving traffic. Although autoscaling automatically adds resources when metrics like CPU usage or request latency cross defined thresholds, performance relief is not instantaneous due to this startup time.
For containerized applications, a rollback involves redeploying a previous image version from a registry, whereas for infrastructure as code, it involves reverting to a prior commit in a configuration repository. In both approaches, the rollback restores service by applying an earlier stable configuration, provided that prior versions have been preserved and tested.
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