Understanding Cloud Characteristics - Deploying and Managing a Cloud Infrastructure - page 21

form of associated system metadata is the MD5 checksum of the object's raw data, which
is used to establish authenticity of the object when it's accessed and downloaded to a client
machine. Encryption has become a necessity, and every public cloud provider now has it
built in, with the option to turn it on or off. Cloud tenants can also pick and choose which
buckets, for example, to encrypt and which buckets to leave as is. An important thing to
note here is that this type of system-generated metadata is derived from the security policy
the tenant has specified. System metadata key-value pairs cannot be modified by the cloud
tenant. Table 1.1 lists some of the system defined metadata.

TABLE 1.1 Example of system-defined metadata

Key Value

Date Object creation date stamp

Content-Length Size of the object in bytes

Last-Modified Update/modification date stamp

Content MD-5 MD5 checksum

On top of this metadata, the tenant can create additional key-value pairs. For example,
if you are operating a video site, a straightforward way to maintain information about the
media files you have stored as objects on S3 would be to create key-value pairs for each
piece of information you would like to associate with a media file, which may include title,
genre, length in seconds, and a short description of the media file, as shown in Table 1.2.
This way, you would just keep the object ID of this media file in another database and
whenever you access the media file, you would simply fetch the metadata of it to fill in
the details.

TABLE 1.2 Example of user-defined metadata

Key Value

Title Title of the video file

Length Length in seconds of the video file

Genre Genre information

Short-Description Short description of the video