FetchHDFS

Description:

Retrieves a file from HDFS. The content of the incoming FlowFile is replaced by the content of the file in HDFS. The file in HDFS is left intact without any changes being made to it.

Tags:

hadoop, hcfs, hdfs, get, ingest, fetch, source

Properties:

In the list below, the names of required properties appear in bold. Any other properties (not in bold) are considered optional. The table also indicates any default values, and whether a property supports the NiFi Expression Language.

Display NameAPI NameDefault ValueAllowable ValuesDescription
Hadoop Configuration ResourcesHadoop Configuration ResourcesA file or comma separated list of files which contains the Hadoop file system configuration. Without this, Hadoop will search the classpath for a 'core-site.xml' and 'hdfs-site.xml' file or will revert to a default configuration. To use swebhdfs, see 'Additional Details' section of PutHDFS's documentation.

This property expects a comma-separated list of file resources.

Supports Expression Language: true (will be evaluated using variable registry only)
Kerberos Credentials Servicekerberos-credentials-serviceController Service API:
KerberosCredentialsService
Implementation: KeytabCredentialsService		Specifies the Kerberos Credentials Controller Service that should be used for authenticating with Kerberos
Kerberos User Servicekerberos-user-serviceController Service API:
KerberosUserService
Implementations: KerberosPasswordUserService
KerberosKeytabUserService
KerberosTicketCacheUserService		Specifies the Kerberos User Controller Service that should be used for authenticating with Kerberos
Kerberos PrincipalKerberos PrincipalKerberos principal to authenticate as. Requires nifi.kerberos.krb5.file to be set in your nifi.properties
Supports Expression Language: true (will be evaluated using variable registry only)
Kerberos KeytabKerberos KeytabKerberos keytab associated with the principal. Requires nifi.kerberos.krb5.file to be set in your nifi.properties

This property requires exactly one file to be provided..

Supports Expression Language: true (will be evaluated using variable registry only)
Kerberos PasswordKerberos PasswordKerberos password associated with the principal.
Sensitive Property: true
Kerberos Relogin PeriodKerberos Relogin Period4 hoursPeriod of time which should pass before attempting a kerberos relogin. This property has been deprecated, and has no effect on processing. Relogins now occur automatically.
Supports Expression Language: true (will be evaluated using variable registry only)
Additional Classpath ResourcesAdditional Classpath ResourcesA comma-separated list of paths to files and/or directories that will be added to the classpath and used for loading native libraries. When specifying a directory, all files with in the directory will be added to the classpath, but further sub-directories will not be included.

This property expects a comma-separated list of resources. Each of the resources may be of any of the following types: file, directory.
HDFS FilenameHDFS Filename${path}/${filename}The name of the HDFS file to retrieve
Supports Expression Language: true (will be evaluated using flow file attributes and variable registry)
Compression codecCompression codecNONE
  • NONE No compression
  • DEFAULT Default ZLIB compression
  • BZIP BZIP compression
  • GZIP GZIP compression
  • LZ4 LZ4 compression
  • LZO LZO compression - it assumes LD_LIBRARY_PATH has been set and jar is available
  • SNAPPY Snappy compression
  • AUTOMATIC Will attempt to automatically detect the compression codec.
No Description Provided.

Relationships:

NameDescription
successFlowFiles will be routed to this relationship once they have been updated with the content of the HDFS file
comms.failureFlowFiles will be routed to this relationship if the content of the HDFS file cannot be retrieve due to a communications failure. This generally indicates that the Fetch should be tried again.
failureFlowFiles will be routed to this relationship if the content of the HDFS file cannot be retrieved and trying again will likely not be helpful. This would occur, for instance, if the file is not found or if there is a permissions issue

Reads Attributes:

None specified.

Writes Attributes:

NameDescription
hdfs.failure.reasonWhen a FlowFile is routed to 'failure', this attribute is added indicating why the file could not be fetched from HDFS
hadoop.file.urlThe hadoop url for the file is stored in this attribute.

State management:

This component does not store state.

Restricted:

Required PermissionExplanation
read distributed filesystemProvides operator the ability to retrieve any file that NiFi has access to in HDFS or the local filesystem.

Input requirement:

This component requires an incoming relationship.

System Resource Considerations:

None specified.

See Also:

ListHDFS, GetHDFS, PutHDFS