Node.js to Bun: migration with real benchmarks, compatibility checks, and rollback

A reliable Bun migration is not a runtime swap. It is an engineering change with compatibility validation and measurable performance criteria.

Candidate selection

Start with low-risk services: limited native addons, strong tests, isolated deployment.

Compatibility checks

bun install
bun test
bun run build
bun run start

Common pitfalls

• native modules (node-gyp) instability;
• runtime behavior drift between V8 and JSC.

Benchmark baseline

Measure p95 latency, throughput, memory, cold start, and error rate under same resource limits.

autocannon -c 100 -d 30 http://127.0.0.1:3000/health

Rollout and rollback

Use canary + SLO guardrails and keep Node image ready for instant rollback.

Final takeaway

Bun can improve performance and developer throughput, but only incremental, measured migration keeps production risk under control.

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