To manage components running on a specific host, click one of the FQDNs listed on the Hosts page. For example, if you click c6403.ambari.apache.org, that host's page appears. Clicking the Summary tab displays a Components pane that lists all components installed on that host:

To manage all of the components on a single host, you can use the Host Actions control at the top right of the display to start, stop, restart, delete, or turn on maintenance mode for all components installed on the selected host.

Alternatively, you can manage components individually, by using the drop-down menu shown next to an individual component in the Components pane. Each component's menu is labeled with the component's current operating status. Opening the menu displays your available management options, based on that status: for example, you can decommission, restart, or stop the DataNode component for HDFS, as shown here: