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This change will require connector developers to add service declarations to their plugins. This can be done in one of two ways:

• Add one or more ServiceLoader manifest files.
• Add a module-info.java  containing one or more provides … with  directives.
  • See Section 7.7.4 of the Java Language Specification 9 for details
  • Connectors using module-info files without also providing a ServiceLoader manifest will not be accessible in Java 8 environments.

Both of these are well-established Java interfaces for which public documentation should be readily available. Once a service declaration is added, plugins can be released and distributed normally.

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The Connect Worker will have a new configuration: plugin.path.discovery  which can take one of multiple values with the following meanings:

• ONLY_SCAN  : Corresponding to the legacy behavior, in which every class on the plugin.path is scanned on startup for plugins. In addition, a warning will be printed to suggest reconfiguring the worker to HYBRID_WARN. This is intended to silence warnings, and to disable the new code paths if a bug is present.
• HYBRID_WARN : In addition to the legacy scanning behavior, use the new mechanism and print a warning if a class is present via scanning but not via ServiceLoader. If there are no discrepancies, a warning will be printed to suggest reconfiguring the worker with SERVICE_LOAD . This is intended to inform operators that they are depending on out-of-date plugins that need to be updated.
• HYBRID_FAIL : Same as HYBRID_WARN , except a discrepancy between the old and new mechanisms will cause a worker to fail to start up, instead of appearing at runtime as a missing plugin. This is intended for use in downstream unit and packaging tests to assert that all plugins have been updated.
• SERVICE_LOAD : Only use the new ServiceLoader mechanism to load plugins. This is intended for production usage after all plugins have been updated, and will be the only mode with performance benefits.

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