Removing configurability of Jenkins.agentProtocols

[jglick]

I ran into a case where a CloudBees CI customer was missing a proprietary agent protocol (see #8621). It seems that this was quite inadvertent: they had in the past exported a JCasC bundle that included something like

jenkins:
  agentProtocols:
  - Ping
  - JNLP4-connect

despite never having touched this configuration section, and without paying attention to this line had committed it to SCM, where it prevented new protocols from appearing! (You can find lots of similar examples, some outdated, by searching.)

The history here is long and tortured (#2010, #2950, #3188, #4387, #7451, etc.) but essentially there was a period of Jenkins development in which new TCP (agent) protocols were being actively developed, and a rather complex opt-in-and-out system was devised to allow administrators to pick which protocol(s) to allow and have that choice be partially preserved across upgrades. But for years now, there has only been JNLP4-connect, and there is no meaningful choice: if you do not wish to allow inbound TCP agents, just disable the port.

The entire protocol selection system seems like technical debt now. This PR just deletes it all and treats AgentProtocol like any other headless extension: whichever protocols are registered by core or plugins are allowed. If a plugin developer wishes to conditionally roll out a protocol behind a feature flag, they can conditionally return null from getName. If an administrator has some weird reason to disable one protocol (but allow others) they could filter it out, but this is not something we would advertise as a supported controller customization.

Testing done

The protocols section in Configure Security is gone.

Proposed changelog entries

• Stop allowing configuration of the list of agent protocols.

Proposed upgrade guidelines

The list of agent protocols is no longer configurable, either through the GUI or JCasC. (Normally there will be two protocols, one for inbound TCP agents, and a ping protocol used to test connectivity.) The agentProtocols section of a JCasC bundle will now be ignored and should be deleted. If you do not wish to allow inbound TCP agents, disable the port rather than the protocol.

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Beta Give feedback

1. The Jira issue, if it exists, is well-described.
2. The changelog entries and upgrade guidelines are appropriate for the audience affected by the change (users or developers, depending on the change) and are in the imperative mood (see examples). Fill in the Proposed upgrade guidelines section only if there are breaking changes or changes that may require extra steps from users during upgrade.
3. There is automated testing or an explanation as to why this change has no tests.
4. New public classes, fields, and methods are annotated with @Restricted or have @since TODO Javadocs, as appropriate.
5. New deprecations are annotated with @Deprecated(since = "TODO") or @Deprecated(forRemoval = true, since = "TODO"), if applicable.
6. New or substantially changed JavaScript is not defined inline and does not call eval to ease future introduction of Content Security Policy (CSP) directives (see documentation).
7. For dependency updates, there are links to external changelogs and, if possible, full differentials.
8. For new APIs and extension points, there is a link to at least one consumer.

Desired reviewers

@mention

Before the changes are marked as ready-for-merge:

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Beta Give feedback

1. There are at least two (2) approvals for the pull request and no outstanding requests for change.
2. Conversations in the pull request are over, or it is explicit that a reviewer is not blocking the change.
3. Changelog entries in the pull request title and/or Proposed changelog entries are accurate, human-readable, and in the imperative mood.
4. Proper changelog labels are set so that the changelog can be generated automatically.
5. If the change needs additional upgrade steps from users, the upgrade-guide-needed label is set and there is a Proposed upgrade guidelines section in the pull request title (see example).
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[jglick]

Apparently forgotten in some earlier cleanup.

[jglick]

Ditto.

[timja]

Makes sense, thanks!

[Vlatombe]

LGTM

[Vlatombe]

/label ready-for-merge

---

This PR is now ready for merge, after ~24 hours, we will merge it if there's no negative feedback.

Thanks!

[MarkEWaite]

This causes test failures in the plugin BOM. The configuration as code plugin shows several test failures with this change. Other plugins may also show failures. I've started a plugin BOM run to check other plugins:

• Test Jenkins weekly 2.483 from master branch bom#3847

Pull requests that need to be included in the plugin BOM run are:

• Removing AgentProtocols support-core-plugin#592
• Removing tests of Jenkins.agentProtocols configuration-as-code-plugin#2580

[jglick]

Sorry, I forgot to mark those two ready for review after this merged. Did that now. CC @timja & @Dohbedoh as likely maintainers.

[MarkEWaite]

Thanks @jglick ! The incremental builds of those plugins passed the plugin BOM tests in

• Test Jenkins weekly 2.483 from master branch bom#3847

I would love to have a release of those two plugins at about the same time as 2.483 releases tomorrow so that the plugin BOM can include those new releases.

[jglick]

Well jenkinsci/configuration-as-code-plugin#2580 is outside my control. jenkinsci/support-core-plugin#592 I could merge myself but would prefer to wait for a review from somebody.