SpotProxy: Rediscovering the Cloud for Censorship Circumvention

SpotProxy's active fleet-management algorithm continuously searches for cheaper Spot and regular VM instances and migrates the proxy fleet to lower-cost options. The paper demonstrates that this approach yields significant cost savings compared to operating a fixed fleet of on-demand instances, while simultaneously improving anti-blocking properties through higher IP churn.

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SpotProxy exploits cloud Spot VMs — instances backed by excess capacity that can be reclaimed at any moment and re-spawned at new IP addresses — to create a high-churn proxy fleet. The observation is that Spot VM preemption, which is an operational liability for normal workloads, is a circumvention asset: it continuously refreshes proxy IP addresses, making censor enumeration and blocklisting structurally ineffective.

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SpotProxy adapts both WireGuard and Snowflake to work with its active proxy migration mechanism, demonstrating that the approach is protocol-agnostic. The active migration mechanism allows clients to move between proxies seamlessly without performance degradation or connection disruption when a proxy is replaced — a requirement for any high-churn proxy infrastructure.

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