Set cache id prefix on installation

[schmengler]

Description (*)

The undocumented id_prefix option for the cache frontend is used to prefix cache keys. If it is not set, Magento uses the first 12 bits of the md5 hash of the absolute path to Magentos app/etc directory. But if this is not exactly the same on all web servers, cache invalidation does not work.

Source: https://github.com/magento/magento2/blob/2.3-develop/lib/internal/Magento/Framework/App/Cache/Frontend/Factory.php#L121-L130

To prevent this issue, the value shall be set on installation, so that the fall back on the fly does not happen anymore. Optionally, the value can be specified explicitly.

Fixed Issues (if relevant)

1. Multisite installation, default website slow (X-Magento-Vary) #15828: Multisite installation, default website slow

Manual testing scenarios (*)

1. Install Magento via CLI or Web Wizard
2. There should be new options "cache-id-prefix" and "page-cache-id-prefix"
3. The value is saved in env.php at cache/frontend/{default,page_cache}/id_prefix

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-cicd2]

All committers have signed the CLA.

[magento-engcom-team]

Hi @schmengler. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me $VERSION instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[schmengler]

To be discussed: what if the behavior to have a cache prefix based on installation dir is desired? This can be the case if a cache for an old release should coexist with a cache for a new release which gets pre-warmed before switching

[slavvka]

Hey @schmengler Thank you for the contribution. It is really a good improvement. The case with pre-warming also fits it since we may decide whether it is generated or set by a user.

[slavvka]

Hey @schmengler GitHub show that you didn't sign up the CLA. Could you do that following the link?

[schmengler]

@slavvka Oh, apparently there's a new CLA that I did not sign yet, did it now!

[magento-engcom-team]

Hi @schmengler. Thank you for your contribution.
We will aim to release these changes as part of 2.3.1.
Please check the release notes for final confirmation.