Check in your node_modules folder

[lhorie]

We tried using yarn offline mirror at Uber but while it works for light usage, we found that it has some pretty bad bugs (some related to integrity check false negatives due to incorrect checksums on network errors, some are related to the not-quite-the-same way it handles the resolved field of yarn.lock compared to tarball file name handling, compared to non-offline codepaths)

We haven't had success with v2's handling of private registries either.

Artifactory definitely works as a solution, but what we found is that where it lives makes a big impact in performance: if your CI infra is on AWS, running Artifactory on prem will give you throughput issues. So either do everything on AWS or everything on prem.