Bol's dev team shares hard lessons from migrating Backstage platform to pnpm

Developers at Dutch retailer bol migrated their internal Backstage developer platform from Yarn 4 to pnpm after five years, seeking better support for parallel Git worktree workflows used with coding agents. While the initial switch — pinning pnpm, replacing commands, and committing a new lockfile — was straightforward, CI pipelines repeatedly downloaded all 4,226 packages from scratch despite a cache being in place. The root cause was a mismatch between where pnpm wrote its store and where GitLab expected to find it, resolved by explicitly setting the store directory within the CI configuration. A further issue emerged when the cached archive ballooned to 1.42 GB across roughly 601,000 files because node_modules trees were included unnecessarily; dropping those reduced cache size by about 72%. The team concluded that package manager migrations surface hidden architectural assumptions, particularly around cache paths and what is actually worth caching.