SHADOW: Seamless Handoff And Zero-Downtime Orchestrated Workload Migration for Stateful Microservices

A new research paper introduces SHADOW (Seamless Handoff And Zero-Downtime Orchestrated Workload Migration), a framework that solves a critical problem in Kubernetes: migrating stateful microservices without downtime. Currently, migrating StatefulSet-managed workloads forces a sequential stop-recreate cycle because two pods with the same ordinal cannot run simultaneously, causing a median of 38.5 seconds of service interruption and risking in-memory state loss.

SHADOW implements a novel Message-based Stateful Microservice Migration (MS2M) approach as a Kubernetes Operator. Its core innovation is the ShadowPod strategy, where a new pod is created from a CRIU checkpoint image on a target node while the original source pod continues serving live traffic. For StatefulSets, an identity swap procedure using an ExchangeFence mechanism re-checkpoints the shadow pod, creates a StatefulSet-owned replacement, and carefully drains message queues to guarantee data integrity.

The framework was rigorously evaluated on a bare-metal Kubernetes cluster with 280 migration runs across four configurations and message rates from 10 to 120 messages per second. Compared to the standard sequential baseline, SHADOW's ShadowPod strategy reduced the restore phase by up to 92%, eliminated service downtime entirely, and cut total migration time by up to 77%. Critically, it achieved zero message loss across all 280 experimental runs, proving its reliability for production environments.