How Vercel Cut Build Wait Times From 90 Seconds To 5

2025-12-15 · Source: ByteByteGo Newsletter · Field: Technology & Digital — Software Development & Engineering, Cloud Computing & IT Infrastructure, Cybersecurity & Data Privacy · Depth: Advanced, long

Summary

Vercel's internal platform, Hive, launched in November 2023, dramatically reduced build provisioning time from 90 seconds to 5 seconds, an 18x improvement. This was achieved by addressing the challenge of hostile multi-tenancy on shared infrastructure, where thousands of customer build scripts run concurrently. Recognizing standard containers like Docker or Kubernetes offered insufficient kernel-level isolation for adversarial workloads, Vercel adopted AWS Firecracker microVMs. Each customer build now runs within an ephemeral "cell" (a microVM) that boots in approximately 125 milliseconds, providing robust, hardware-enforced isolation. The speedup stems from three key optimizations: faster cold boots via cached container images and block device snapshotting, a "warm pool" of pre-booted cells for near-instant provisioning, and Firecracker's inherent low-latency virtualization. This foundational shift, though costly in engineering investment and operational expense for warm pools, also enabled new product features like enhanced build machines and Secure Compute.

Key takeaway

For DevOps or Security Engineers building multi-tenant platforms, you must align your isolation strategy with your threat model. Standard containers are insufficient for hostile multi-tenancy due to shared kernel risks. Instead, consider microVMs like Firecracker for robust, hardware-enforced isolation. This demands significant engineering and operational investment for warm pools. However, it delivers superior security and performance for ephemeral workloads, enabling advanced features and dramatically cutting build wait times.

Key insights

Hostile multi-tenancy demands microVM isolation; speed is achieved by optimizing on this secure, harder architectural foundation.

Principles

• Threat model dictates architecture.
• Ephemeral environments bolster security.
• Accepting harder constraints provides advantage.

Method

Vercel's Hive uses Firecracker microVMs ("cells") for kernel-level isolation, with containers inside. Orchestration by host and cell daemons, with speed from cached images, block snapshotting, and warm pools of pre-booted cells.

In practice

• Adopt microVMs for hostile multi-tenancy.
• Implement warm pools for ephemeral workloads.
• Use block device snapshotting for faster VM starts.

Topics

• Vercel Hive
• Firecracker MicroVMs
• Multi-tenant Isolation
• Build System Optimization
• Warm Pool Architecture
• Cloud Infrastructure

Best for: CTO, VP of Engineering/Data, MLOps Engineer, DevOps Engineer, Software Engineer, Security Engineer

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Editorial summary, takeaway, and curation by AIssential. Original article published by ByteByteGo Newsletter.