Startup failure due to misconfigured unmanaged extensions or plugins
Occasionally, following upgrades, one might encounter Neo4j server initialisation failure due to an exception similar to:
2019-11-14 12:57:40.446+0000 ERROR Failed to start Neo4j: Starting Neo4j failed: Component 'org.neo4j.server.AbstractNeoServer$ServerComponentsLifecycleAdapter@7f7eeaaf' was successfully initialized, but failed to start. Please see the attached cause exception "The ResourceConfig instance does not contain any root resource classes.". Starting Neo4j failed: Component 'org.neo4j.server.AbstractNeoServer$ServerComponentsLifecycleAdapter@7f7eeaaf' was successfully initialized, but failed to start. Please see the attached cause exception "The ResourceConfig instance does not contain any root resource classes.".
This exception is usually thrown in following situations:
When the plugins directory (by default set to $NEO4J_HOME/plugins), contains an invalid plugin JAR.
When the JAR no longer corresponds to the newly upgraded Neo4j version.
When the path defined by dbms.unmanaged_extension_classes is invalid or unreachable.
When the unmanaged extension hosted at the path does not contain the required resource classes as highlighted by the exception.
If using plugins (Neo4j or custom), e.g. using apoc, ensure that there is only one plugin version compatible with the currently installed Neo4j version.
Further, assuming that the present use of any configured unmanaged extensions is not required. Simplest workaround to achieve
server initialisation, halted by the above exception, is to comment this setting in neo4j.conf as #dbms.unmanaged_extension_classes.
If the extension is indeed required, the configuration path and permissions must then be verified and finally the presence of the classes required for the extension to work.
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