cleanup partially initialized pipeline

DRY the plugin registration

typo

log exception message

logstash-core/lib/logstash/pipeline.rb

@@ -141,7 +141,7 @@ def initialize(config_str, settings = SETTINGS, namespaced_metric = nil)
     begin
       @queue = LogStash::QueueFactory.create(settings)
     rescue => e
-      @logger.error("Logstash failed to create queue", "exception" => e, "backtrace" => e.backtrace)
+      @logger.error("Logstash failed to create queue", "exception" => e.message, "backtrace" => e.backtrace)
       raise e
     end
 
@@ -250,12 +250,32 @@ def stopped?
     @running.false?
   end
 
+  # register_plugin simply calls the plugin #register method and catches & logs any error
+  # @param plugin [Plugin] the plugin to register
+  # @return [Plugin] the registered plugin
+  def register_plugin(plugin)
+    plugin.register
+    plugin
+  rescue => e
+    @logger.error("Error registering plugin", :plugin => plugin.inspect, :error => e.message)
+    raise e
+  end
+
+  # register_plugins calls #register_plugin on the plugins list and upon exception will call Plugin#do_close on all registered plugins
+  # @param plugins [Array[Plugin]] the list of plugins to register
+  def register_plugins(plugins)
+    registered = []
+    plugins.each { |plugin| registered << register_plugin(plugin) }
+  rescue => e
+    registered.each(&:do_close)
+    raise e
+  end
+
   def start_workers
     @worker_threads.clear # In case we're restarting the pipeline
     begin
-      start_inputs
-      @outputs.each {|o| o.register }
-      @filters.each {|f| f.register }
+      register_plugins(@outputs)
+      register_plugins(@filters)
 
       pipeline_workers = safe_pipeline_worker_count
       batch_size = @settings.get("pipeline.batch.size")
@@ -286,6 +306,16 @@ def start_workers
           worker_loop(batch_size, batch_delay)
         end
       end
+
+      # inputs should be started last, after all workers
+      begin
+        start_inputs
+      rescue => e
+        # if there is any exception in starting inputs, make sure we shutdown workers.
+        # exception will already by logged in start_inputs
+        shutdown_workers
+        raise e
+      end
     ensure
       # it is important to guarantee @ready to be true after the startup sequence has been completed
       # to potentially unblock the shutdown method which may be waiting on @ready to proceed
@@ -335,7 +365,7 @@ def filter_batch(batch)
     # Users need to check their configuration or see if there is a bug in the
     # plugin.
     @logger.error("Exception in pipelineworker, the pipeline stopped processing new events, please check your filter configuration and restart Logstash.",
-                  "exception" => e, "backtrace" => e.backtrace)
+                  "exception" => e.message, "backtrace" => e.backtrace)
 
     raise e
   end
@@ -378,10 +408,11 @@ def start_inputs
     end
     @inputs += moreinputs
 
-    @inputs.each do |input|
-      input.register
-      start_input(input)
-    end
+    # first make sure we can register all input plugins
+    register_plugins(@inputs)
+
+    # then after all input plugins are sucessfully registered, start them
+    @inputs.each { |input| start_input(input) }
   end
 
   def start_input(plugin)
@@ -395,20 +426,20 @@ def inputworker(plugin)
     rescue => e
       if plugin.stop?
         @logger.debug("Input plugin raised exception during shutdown, ignoring it.",
-                      :plugin => plugin.class.config_name, :exception => e,
+                      :plugin => plugin.class.config_name, :exception => e.message,
                       :backtrace => e.backtrace)
         return
       end
 
       # otherwise, report error and restart
       if @logger.debug?
         @logger.error(I18n.t("logstash.pipeline.worker-error-debug",
-                             :plugin => plugin.inspect, :error => e.to_s,
+                             :plugin => plugin.inspect, :error => e.message,
                              :exception => e.class,
                              :stacktrace => e.backtrace.join("\n")))
       else
         @logger.error(I18n.t("logstash.pipeline.worker-error",
-                             :plugin => plugin.inspect, :error => e))
+                             :plugin => plugin.inspect, :error => e.message))
       end
 
       # Assuming the failure that caused this exception is transient,