NIFI-520 added explanation of enabling and disabling controller services. Also fixed images in that section and added some explanation about file expiration in the Connecting Components section.

nifi/nifi-docs/src/main/asciidoc/user-guide.adoc

@@ -70,7 +70,7 @@ Terminology
 	This allows data to be routed in different ways based on its processing outcome. Each connection houses a FlowFile Queue.
 	When a FlowFile is transferred to a particular Relationship, it is added to the queue belonging to the associated Connection.
 
-*Controller Service*: Controller Services are extension points that, after being added and configured by a DFM in the User Interface, will start up when NiFi starts up and provide information for use by other components (processors). A common Controller Service used by several processors is the StandardSSLContextService. It provides the ability to configure keystore and/or truststore properties once and reuse that configuration throughout the application. The idea is that, rather than configure this information in every processor that might need it, the controller service provides it for any processor to use as needed.
+*Controller Service*: Controller Services are extension points that, after being added and configured by a DFM in the User Interface, will start up when NiFi starts up and provide information for use by other components (such as processors or other controller services). A common Controller Service used by several components is the StandardSSLContextService. It provides the ability to configure keystore and/or truststore properties once and reuse that configuration throughout the application. The idea is that, rather than configure this information in every processor that might need it, the controller service provides it for any processor to use as needed.
 
 *Reporting Task*: Reporting Tasks run in the background to provide statistical reports about what is happening in the NiFi instance. The DFM adds and configures Reporting Tasks in the User Interface as desired. Common reporting tasks include the ControllerStatusReportingTask, MonitorDiskUsage reporting task, MonitorMemory reporting task, and the StandardGangliaReporter.
 
@@ -480,13 +480,15 @@ image:configure-controller-service-properties.png["Configure Controller Service
 
 The Comments tab is just an open-text field, where the DFM may include comments about the service. After configuring a Controller Service, click the Apply button to apply the configuration and close the window, or click the Cancel button to cancel the changes and close the window.
 
-The Reporting Tasks tab behaves exactly the same way as the Controller Services tab. The DFM has the option to add Reporting Tasks and configure them in the same way as Controller Services.
+Note that after a Controller Service has been configured, it must be enabled in order to run. Do this using the Enable button in the far-right column of the Controller Services tab of the Controller Settings window. Then, in order to modify an existing/running controller service, the DFM needs to stop/disable it (as well as all referencing processors, reporting tasks, and controller services). Rather than having to hunt down each component that is referenced by that controller service, the DFM has the ability to stop/disable them when disabling the controller service in question. Likewise, when enabling a controller service, the DFM has the option to start/enable all referencing processors, reporting tasks, and controller services.
+
+The Reporting Tasks tab behaves similarly to the Controller Services tab. The DFM has the option to add Reporting Tasks and configure them in the same way as Controller Services.
 
 image:reporting-tasks-tab.png["Reporting Tasks Tab", width=900]
 
 Once a Reporting Task has been added, the DFM may configure it by clicking the Edit (pencil icon) in the far-right column. Other buttons in this column include the Start button, Remove button, and Usage button, which links to the documentation for the particular Reporting Task.
 
-image:reporting-tasks-edit-buttons.png["Reporting Tasks Buttons"]
+image:reporting-tasks-edit-buttons2.png["Reporting Tasks Buttons"]
 
 When the DFM clicks the Edit button, a Configure Reporting Task window opens. It has three tabs: Settings, Properties, and Comments. This window is also similar to the Configure Processor window. The Settings tab provides a place for the DFM to give the Reporting Task a unique name (if desired). It also lists a UUID for the Reporting Task and provides settings for the task's Scheduling Strategy and Run Schedule (similar to the same settings in a processor). The DFM may hover the mouse over the question mark icons to see more information about each setting.
 
@@ -544,8 +546,8 @@ that are active for the Connection.
 File expiration is a concept by which data that cannot be processed in a timely fashion can be automatically removed from the flow.
 This is useful, for example, when the volume of data is expected to exceed the volume that can be sent to a remote site.
 In this case, the expiration can be used in conjunction with Prioritizers to ensure that the highest priority data is
-processed first and then anything that cannot be processed within a certain time period (one hour, for example) can be dropped. The default
-value of `0 sec` indicates that the data will never expire.
+processed first and then anything that cannot be processed within a certain time period (one hour, for example) can be dropped. The expiration period is based on the time that the data entered the NiFi instance. In other words, if the file expiration on a given connection is set to '1 hour', and a file that has been in the NiFi instance for one hour reaches that connection, it will expire. The default
+value of `0 sec` indicates that the data will never expire. When a file expiration other than '0 sec' is set, a small clock icon appears on the connection label, so the DFM can see it at-a-glance when looking at a flow on the graph.
 
 
 NiFi provides two configuration elements for Back Pressure. These thresholds indicate how much data should be