Current Output plugin base class has a probrem that it needs router method if secondary uses router.

[joker1007]

• fluentd (v0.14.7)
• All envs

Current Fluent::Plugin::Output has following statement in configure method.

          @secondary.router = router if @secondary.has_router?

In current version, If secondary output uses compat layer (compat layer always include :event_emitter) or secondary output uses :event_emitter helper, primary output always needs :event_emitter.
In short, If user wants to use secondary output, almost output plugin needs :event_emitter at present.