Cluster Management - Big Data Made Easy: A Working Guide to the Complete Hadoop Toolset - page 244

Figure 8-24. Status of Cloudera hosts
Click the Host page's Parcels option and you'll see the available parcels that can be installed. Parcels are provided
by Cloudera from CDH4. They provide a mechanism for installing software updates without causing down time for
the Hadoop cluster. They are actually a gzipped tar file bundle of software supplied by Cloudera in its own format,
as are many of the downloaded and unpacked releases mentioned in this topic. The difference is that Cloudera adds
metadata to the parcel, which is extra information so that the Cloudera manager knows what to do with the parcel.
The Parcels display as shown in Figure 8-25 checks on the availability of new parcels via a menu option.
The release of new software parcels to your cluster then just becomes a cycle of downloading those new parcels,
distributing them to the cluster, and activating them—all accomplished from this single screen. If you remember the
topics in Chapter 2, and all of the effort that went into installing and configuring CDH4, then you'll quickly see how
this software release cycle makes the cluster manager worthwhile.