Reading through the yarn article it seems like Hex does all of this except it does it automatically without needing to configure a mirror.

All Hex packages you download are cached in ~/.hex which means that if your network is down and you need to fetch the package again the cache will be used as a fallback. You can force the cache to be used by setting the environment flag HEX_OFFLINE=1. Additionally, all your dependencies are locked in the mix.lock file to ensure you always get the same versions that were initially fetched and locked.

If you need something else then please elaborate on what you want to do and how it is different from what Hex provides today.

There are multiple layers of caching for the different stages of fetching dependencies. We will always try to use the cache if it’s available but that does not necessarily mean we make no HTTP requests if everything is cached.

First of mix deps.get will not do anything if you already have fetched dependencies in the projects deps/ directory and they match the lock. If dependencies are missing in deps/ or they do not match the lockfile they will be fetched.

Before fetching dependencies we may need to do dependency resolution in case dependencies are not locked or they are being updated with mix deps.update. To perform dependency resolution we need to fetch package indexes from the registry. Package indexes are cached but we will always make conditional HTTP requests [1] for them to ensure you have the latest version of the index, if you have the latest version they are not downloaded again.

When dependencies are resolved to a specific version their package tarballs can be fetched, the tarballs are also cached so if you fetched the tarball previously on the same machine and the checksum matches then no request will be made.

[1] HTTP conditional requests - HTTP | MDN

• To handle when hex is down in CI => set up private repo. ( Self hosted hex repo - #8 by zazaian ) Unfortunately artifactory/nexus do not have them ( Mix deps.get - with Artifactory? )
• To speed up CI by caching => you may cache deps folder.

More notes

• You may just tarball deps folder for example and use HEX_OFFLINE env var. However, I’ve seen its content changes (e.g. creating new file under /deps) during compile time..
• You can easily set up hex repo with mini_repo - but you have to list packages to sync, or sync all.