HDFS Reader

On this Page

Snap type:

Read

Description:

This Snap reads data from HDFS (Hadoop File System) and produces a binary data stream at the output. For the hdfs protocol, please use a SnapLogic on-premises Groundplex and make sure that its instance is within the Hadoop cluster and SSH authentication has already been established. The Snap also supports reading from a Kerberized cluster using the HDFS protocol.

Expected upstream Snaps: [None]
Expected downstream Snaps: Any data transformation or formatting Snaps.
Expected input: [None]
Expected output: A document with the columns and data of the Parquet file.

HDFS 2.4.0 is supported for the HDFS protocol. This Snap supports HDFS, ADL (Azure Data Lake), ABFS(Azure Data Lake Storage Gen 2 ), and WASB(Azure storage) protocols.

Hadoop allows you to configure proxy users to access HDFS on behalf of other users; this is called impersonation. When user impersonation is enabled on the Hadoop cluster, any jobs submitted using a proxy are executed with the impersonated user's existing privilege levels rather than those of the superuser associated with the cluster. For more information on user impersonation in this Snap, see the section on User Impersonation below.

Prerequisites:

[None]

Limitations and Known Issues:

Supports reading from HDFS Encryption.
Works in Ultra Task Pipelines.
The platform does not support generating output previews for files larger than 8KB. This does not mean that the Snap has failed: The file will be read upon the Snap's execution; only the output preview will not be generated upon validation.

Account:

This Snap uses account references created on the Accounts page of SnapLogic Manager to handle access to this endpoint. This Snap supports Azure storage account, Azure Data Lake account, Kerberos account, or no account. Account types supported by each protocol are as follows:

Protocol	Account types	Documentation
wasb	Azure Storage	Azure Storage
wasbs	Azure Storage	Azure Storage
adl	Azure Data Lake	Azure Data Lake
hdfs	Kerberos	Kerberos

Required settings for account types are as follows:

Account Type	Settings
Azure Storage	Account name, Primary access key
Azure Data Lake	Tenant ID, Access ID, Secret Key
Kerberos Account	Client Principal, Service Principal, Keytab File

IAM Roles for Amazon EC2

global.properties

jcc.jvm_options = -DIAM_CREDENTIAL_FOR_S3=TRUE

Please note this feature is supported in only in Groundplex nodes hosted in the EC2 environment.

For more information on IAM Roles, see http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/iam-roles-for-amazon-ec2.html

Kerberos Account UI Configuration

The security model configured for the Groundless (SIMPLE or KERBEROS authentication) must match the security model of the remote server. Due to limitations of the Hadoop library we are only able to create the necessary internal credentials for the configuration of the Groundplex.

Views:

Input	This Snap has at most one document input view. It may contain values for the File expression property.
Output	This Snap has exactly one binary output view and provides the binary data stream read from the specified sources. Examples of Snaps that can be connected to this output are CSV Parser, JSON Parser, and XML Parser.
Error	This Snap has at most one document error view and produces zero or more documents in the view.

Settings

Label

Required. Specify the name for the Snap. You can modify this to be more specific, especially if you have more than one of the same Snap in your pipeline.

Directory

Specify the URL for the data source (directory). The Snap supports the following protocols.

hdfs://<hostname>:<port>/<path to directory>/
wasb:///<container name>/<path to directory>/
wasbs:///<container name>/<path to directory>/
adl://<container name>/<path to directory>/
abfs:///<filesystem>/<path>/
abfs://<filesystem>@<accountname>.<endpoint>/<path>
abfss:///<filesystem>/<path>/
abfss://<filesystem>@<accountname>.<endpoint>/<path>

When you use the ABFS protocol to connect to an endpoint, the account name and endpoint details provided in the URL override the corresponding values in the Account Settings fields.

The Directory property is not used in the pipeline execution or preview and used only in the Suggest operation. When you press the Suggest icon, it will display a list of subdirectories under the given directory. It generates the list by applying the value of the Filter property.

Examples:

hdfs://ec2-54-198-212-134.compute-1.amazonaws.com:8020/user/john/input
$filename
wasb:///snaplogic/testDir/
wasbs:///snaplogic/testDir/
adl://snapqa/
abfs:///filesystem2/dirl/a+b
abfss:///filesystem2/dirl/a+b

Default value: hdfs://<hostname>:<port>/

SnapLogic automatically appends "azuredatalakestore.net" to the store name you specify when using Azure Data Lake; therefore, you do not need to add 'azuredatalakestore.net' to the URI while specifying the directory.

File Filter

Specify the Glob filter pattern.

Use glob patterns to display a list of directories or files when you click the Suggest icon in the Directory or File property. A complete glob pattern is formed by combining the value of the Directory property with the Filter property. If the value of the Directory property does not end with "/", the Snap appends one, so that the value of the Filter property is applied to the directory specified by the Directory property.

Glob Pattern Interpretation Rules

The following rules are used to interpret glob patterns:

The * character matches zero or more characters of a name component without crossing directory boundaries. For example, the *.csv pattern matches a path that represents a file name ending in .csv, and *.* matches all file names that contain a period.

The ** characters match zero or more characters across directories; therefore, it matches all files or directories in the current directory and in its subdirectories. For example, /home/** matches all files and directories in the /home/ directory.

The ? character matches exactly one character of a name component. For example, 'foo.?' matches file names that start with 'foo.' and are followed by a single-character extension.

The \ character is used to escape characters that would otherwise be interpreted as special characters. The expression \\ matches a single backslash, and \{ matches a left brace, for example.

The ! character is used to exclude matching files from the output.

The [ ] characters form a bracket expression that matches a single character of a name component out of a set of characters. For example, '[abc]' matches 'a', 'b', or 'c'. The hyphen (-) may be used to specify a range, so '[a-z]' specifies a range that matches from 'a' to 'z' (inclusive). These forms can be mixed, so '[abce-g]' matches 'a', 'b', 'c', 'e', 'f' or 'g'. If the character after the [ is a ! then it is used for negation, so '[!a-c]' matches any character except 'a', 'b', or 'c'.

Within a bracket expression, the '*', '?', and '\' characters match themselves. The '-' character matches itself if it is the first character within the brackets, or the first character after the !, if negating.

The '{ }' characters are a group of sub-patterns where the group returns a match if any sub-pattern in the group matches the contents of a target directory. The ',' character is used to separate sub-patterns. Groups cannot be nested. For example, the pattern '*.{csv, json}' matches file names ending with '.csv' or '.json'.

Leading dot characters in a file name are treated as regular characters in match operations. For example, the '*' glob pattern matches file name ".login".

All other characters match themselves.

Examples:

'*.csv' matches all files with a csv extension in the current directory only.

'**.csv' matches all files with a csv extension in the current directory and in all its subdirectories.

*[!{.pdf,.tmp}] excludes all files with the extension PDF or TMP.

File

The name of the file to be read. This can also be a relative path under the directory given in the Directory property. It should not start with a URL separator "/".
The File property can be a JavaScript expression which will be evaluated with values from the input view document. When you press the Suggest icon, it will display a list of regular files under the directory in the Directory property. It generates the list by applying the value of the Filter property.
If this property is left blank (the * wildcard is used) when the Snap is executed, all files under the directory matching the glob filter will be read.
Example:

sample.csv
tmp/another.csv
$filename
_filename

Default value: [None]

User Impersonation

Select this check box to enable user impersonation.

For encryption zones, use user impersonation.

Default value: Not selected

For more information on working with user impersonation, click the link below.

User Impersonation Details

Generic User Impersonation Behavior

When the User Impersonation check box is selected, and Kerberos is the account type, the Client Principal configured in the Kerberos account impersonates the pipeline user.

When the User Impersonation option is selected, and Kerberos is not the account type, the user executing the pipeline is impersonated to perform HDFS Operations. For example, if the user logged into the SnapLogic platform is operator@snaplogic.com, the user name "operator" is used to proxy the super user.

User impersonation behavior on pipelines running on Groundplex with a Kerberos account configured in the Snap

When the User Impersonation checkbox is selected in the Snap, it is the pipeline user who performs the file operation. For example, if the user logged into the SnapLogic platform is operator@snaplogic.com, the user name "operator" is used to proxy the super user.
When the User Impersonation checkbox is not selected in the Snap, the Client Principal configured in the Kerberos account performs the file operation.

For non-Kerberised clusters, you must activate Superuser access in the Configuration settings.

HDFS Snaps support the following accounts:

Azure storage account
Azure Data Lake account
Kerberos account
No account

When an account is configured with an HDFS Snap, user impersonation settings have no impact on all accounts, except the Kerberos account.

Number Of Retries

Specify the maximum number of attempts to be made to receive a response.

The request is terminated if the attempts do not result in a response.
When the number of retries are exhausted, the Snap writes the error to the error view.
Retry operation, which is the attempts to receive a response occurs only when the Snap loses the connection with the server.

Default value: 0

Retry Interval (seconds)

Specify the time interval between two successive retry requests. A retry happens only when the previous attempt resulted in an exception.

Default value: 1

Snap execution

Select one of the three following modes in which the Snap executes: Available options are:

Validate & Execute: Performs limited execution of the Snap and generates a data preview during Pipeline validation; then performs full execution of the Snap (unlimited records) during Pipeline runtime.
Execute only: Performs full execution of the Snap during Pipeline execution without generating preview data.
Disabled: Disables the Snap and all Snaps downstream from it.

Troubleshooting

Writing to S3 files with HDFS version CDH 5.8 or later

When running HDFS version later than CDH 5.8, the Hadoop Snap Pack may fail to write to S3 files. To overcome this, make the following changes in the Cloudera manager:

Go to HDFS configuration.
In Cluster-wide Advanced Configuration Snippet (Safety Valve) for core-site.xml, add an entry with the following details:
- Name: fs.s3a.threads.max
- Value: 15
Click Save.
Restart all the nodes.
Under Restart Stale Services, select Re-deploy client configuration.
Click Restart Now.

Click to view/expand

Release	Snap Pack Version	Date	Type	Updates
February 2024	436patches25902	10 Apr 2024	Latest	Fixed a memory management issue in the HDFS Writer, HDFS ZipFile Writer, ORC Writer, and Parquet Writer Snaps, which previously caused out-of-memory errors when multiple Snaps were used in the pipeline. The Snap now conducts a pre-allocation memory check, dynamically adjusting the write buffer size based on available memory resources when writing to ADLS.
February 2024	435patches25410	06 Mar 2024	Latest	Enhanced the AWS S3 Account for Hadoop with an External ID that enables you to access Hadoop resources securely.
February 2024	main25112	14 Feb 2024	Stable	Updated and certified against the current SnapLogic Platform release.
November 2023	435patches23904	20 Nov 2023	Latest	Fixed an issue with the Parquet Writer Snap that displayed an error `Failed to write parquet data` when the decimal value passed from the second input view exceeded the specified scale. Fixed an issue with the Parquet Writer Snap that previously failed to handle the conversion of BigInt/int64 (larger numbers) after the 4.35 GA now converts them accurately.
November 2023	435patches23780	15 Nov 2023	Latest	Fixed an issue related to error routing to the output view. Also fixed a connection timeout issue.
November 2023	main23721	08 Nov 2023	Stable	Updated and certified against the current SnapLogic Platform release.
August 2023	434patches23173	11 Oct 2023	Latest	Enhanced the Parquet Writer Snap with a Decimal Rounding Mode dropdown list to enable the rounding method for decimal values when the number exceeds the required decimal places.
August 2023	434patches22662	25 Aug 2023	Latest	Enhanced the Parquet Writer Snap with the support for LocalDate and DateTime. The Snap now shows the schema suggestions for LocalDate and DateTime correctly. Enhanced the Parquet Reader Snap with the Use datetime types checkbox that supports LocalDate and DateTime datatypes. Behavior change: When you select the Use datetime types checkbox in the Parquet Reader Snap, the Snap displays the LocalDate and DateTime in the output for INT32 (DATE) and INT64 (TIMESTAMP_MILLIS) columns. When you deselect this checkbox, the columns retain the previous datatypes and display `string` and `integer` values in the output.
August 2023	main22460	16 Aug 2023	Stable	Updated and certified against the current SnapLogic Platform release.
May 2023	433patches22180	08 Aug 2023	Latest	Introduced the HDFS Delete, which deletes the specified file, group of files, or directory from the supplied path and protocol in the Hadoop Distributed File System (HDFS).
May 2023	433patches21494	14 Jun 2023	Latest	The Hadoop Directory Browser Snap now returns all the output documents as expected after implementing pagination for the ABFS protocol.
May 2023	main21015	10 May 2023	Stable	Upgraded with the latest SnapLogic Platform release.
February 2023	432patches20820	28 Apr 2023	Latest	Fixed an authorization issue that occurs with the Parquet Writer Snap when it receives empty document input.
February 2023	432patches20209	31 Mar 2023	Latest	The Apache Commons Compress library has been upgraded to version 1.22.
February 2023	432patches20139	09 Mar 2023	Latest	The Kerberos Account that is available for a subset of snaps in the Hadoop Snap pack now supports a configuration that enables you to read from and write to the Hadoop Distributed File System (HDFS) managed by multiple Hadoop clusters. You can specify the location of the Hadoop configuration files in the Hadoop config directory field. The value in this field overrides the value that is set on the Snaplex system property used for configuring a single cluster.
February 2023	main19844	09 Feb 2023	Stable	Upgraded with the latest SnapLogic Platform release.
November 2022	main18944	10 Nov 2022	Stable	The AWS S3 and S3 Dynamic accounts now support a maximum session duration of an IAM role defined in AWS.
August 2022	main17386	11 Aug 2022	Stable	Extended the AWS S3 Dynamic Account support to ORC Reader and ORC Writer Snaps to support AWS Security Token Service (STS) using temporary credentials.
4.29 Patch	429patches16630	21 Jul 2022	Latest	Extended the AWS S3 Dynamic Account support to ORC Reader and ORC Writer Snaps to support AWS Security Token Service (STS) using temporary credentials. Fixed an issue in the following Snaps that use AWS S3 dynamic account, where the Snaps displayed the security credentials like Access Key, Secret Key, and Security Token in the logs. Now, the security credentials in the logs are blurred for the Snaps that use AWS S3 dynamic account. ORC Reader ORC Writer Parquet Reader Parquet Writer
4.29	main15993	14 May 2022	Stable	Enhanced the AWS S3 Account for Hadoop account to include the S3 Region field that allows cross-region or proxied cross-region access to S3 buckets in the Parquet Reader and Parquet Writer Snaps.
4.28 Patch	428patches15216	23 Mar 2022	Latest	Added the AWS S3 Dynamic account for Parquet Reader and Parquet Writer Snaps.
4.28	main14627	12 Feb 2022	Stable	Upgraded with the latest SnapLogic Platform release.
4.27 Patch	427patches13769	25 Jan 2022	Latest	Fixed an issue with the Hadoop Directory Browser Snap where the Snap was not listing the files in the given directory for Windows VM.
4.27 Patch	427patches12999	23 Nov 2021	Latest	Enhanced the Parquet Reader Snap with int96 As Timestamp checkbox, which when selected enables the Date Time Format field. You can use this field to specify a date-time format of your choice for int96 data-type fields. The int96 As Timestamp checkbox is available only when you deselect Use old data format checkbox.
4.27	main12833	13 Nov 2021	Stable	Enhanced the Parquet Writer and Parquet Reader Snaps with Azure SAS URI properties, and Azure Storage Account for Hadoop with SAS URI Auth Type. This enables the Snaps to consider SAS URI given in the settings if the SAS URI is selected in the Auth Type during account configuration.
4.26	426patches12288	19 Oct 2021	Latest	Fixed a memory leak issue when using HDFS protocol in Hadoop Snaps.
4.26	main11181	14 Aug 2021	Stable	Upgraded with the latest SnapLogic Platform release.
4.25 Patch	425patches9975	07 Jun 2021	Latest	Fixed the dependency issue in Hadoop Parquet Reader Snap while reading from AWS S3. The issue is caused due to conflicting definitions for some of the AWS classes (dependencies) in the classpath.
4.25	main9554	08 May 2021	Stable	Enhanced the HDFS Reader and HDFS Writer Snaps with the Retry mechanism that includes the following settings: Number of Retries: Specifies the maximum number of retry attempts when the Snap fails to connect to the Hadoop server. Retry Interval (seconds): Specifies the minimum number of seconds the Snap must wait before each retry attempt.
4.24 Patch	424patches9262	26 Apr 2021	Latest	Enhanced the AWS S3 Account for Hadoop to support role-based access when you select IAM role checkbox.
4.24 Patch	424patches8876	11 Mar 2021	Latest	Fixes the missing library error in Hadoop Snap Pack when running Hadoop Pipelines in JDK11 runtime.
4.24	main8556	13 Feb 2021	Stable	Upgraded with the latest SnapLogic Platform release.
4.23 Patch	423patches7440	01 Dec 2020	Latest	Fixes the issue in HDFS Reader Snap by supporting to read and write files larger than 2GB using ABFS(S) protocol.
4.23	main7430	14 Nov 2020	Stable	Upgraded with the latest SnapLogic Platform release.
4.22	main6403	12 Sep 2020	Stable	Upgraded with the latest SnapLogic Platform release.
4.21 Patch	hadoop8853	28 May 2020	Latest	Updates the Parquet Writer and Parquet Reader Snaps to support the yyyy-MM-dd format for the DATE logical type.
4.21	snapsmrc542	09 May 2020	Stable	Upgraded with the latest SnapLogic Platform release.
4.20 Patch	hadoop8776	30 Mar 2020	Latest	Updates the Hadoop Snap Pack to use the latest version of org.xerial.snappy:snappy-java for compression type Snappy, in order to resolve the java.lang.UnsatisfiedLinkError: org.xerial.snappy.SnappyNative.maxCompressedLength(I)I error.
4.20	snapsmrc535	08 Feb 2020	Stable	Upgraded with the latest SnapLogic Platform release.
4.19 Patch	hadoop8270	23 Dec 2019	Latest	Fixes an issue with the Hadoop Parquet Writer Snap wherein the Snap throws an exception when the input document includes one or all of the following: Empty lists. Lists with all null values. Maps with all null values.
4.19	snaprsmrc528	14 Nov 2019	Stable	Upgraded with the latest SnapLogic Platform release.
4.18 Patch	hadoop8033	15 Oct 2019	Latest	Fixed an issue with the Parquet Writer Snap wherein the Snap throws an error when working with WASB protocol.
4.18	snapsmrc523	10 Aug 2019	Stable	Added ADLS Gen2 support for ABFS (Azure Blob File System) and ABFSS protocols to the HDFS ZipFile Reader, HDFS ZipFile Writer, HDFS Reader, ORC Reader, Parquet Reader, and Hadoop Directory Browser Snaps. Added ADLS Gen2 support for ABFS (Azure Blob File System) and ABFSS protocols.
4.17	ALL7402	11 Jun 2019	Latest	Pushed automatic rebuild of the latest version of each Snap Pack to SnapLogic UAT and Elastic servers.
4.17	snapsmrc515	11 Jun 2019	Latest	Added the Snap Execution field to all Standard-mode Snaps. In some Snaps, this field replaces the existing Execute during preview check box.
4.16	snapsmrc508	16 Feb 2019	Stable	Added a new property, Output for each file written, to handle multiple binary input data in the HDFS Writer Snap.
4.15	snapsmrc500	15 Dec 2018	Stable	Added two new Snaps: HDFS ZipFile Reader and HDFS ZipFile Writer. Added support for the Data Catalog Snaps in Parquet Reader and Parquet Writer Snaps.
4.14 Patch	hadoop5888	02 Oct 2018	Latest	Fixed an issue wherein the Hadoop snaps were throwing an exception when a Kerberized account is provided, but the snap is run in a non-kerberized environment.
4.14	snapsmrc490	11 Aug 2018	Stable	Added the Hadoop Directory Browser Snap, which browses a given directory path in the Hadoop file system using the HDFS protocol and generates a list of all the files in the directory. It also lists subdirectories and their contents. Added support for S3 file protocol in the ORC Reader, and ORC Writer Snaps. Added support for reading nested schema in the Parquet Reader Snap.
4.13 Patch	hadoop5318	21 Jun 2018	Latest	Fixed the HDFS Reader/Writer and Parquet Reader/Writer Snaps, wherein Hadoop configuration information does not parse from the client's configuration files. Fixed the HDFS Reader/Writer and Parquet Reader/Writer Snaps, wherein User Impersonation does not work on Hadooplex.
4.13	snapsmrc486	12 May 2018	Stable	KMS encryption support added to AWS S3 account in the Hadoop Snap Pack. Enhanced the Parquet Reader, Parquet Writer, HDFS Reader, and HDFS Writer Snaps to support WASB and ADLS file protocols. Added the AWS S3 account support to the Parquet Reader and Writer Snaps. Added second input view to the Parquet Reader Snap that when enabled, accepts table schema. Supported with AWS S3, Azure Data Lake, and Azure Storage Accounts.
4.12 Patch	hadoop5132	20 Nov 2017	Latest	Fixed an issue with the HDFS Reader Snap wherein the pipeline becomes stale while writing to the output view.
4.12	snapsmrc480	17 Feb 2018	Stable	Upgraded with the latest SnapLogic Platform release.
4.11 Patch	hadoop4275		Latest	Addressed an issue with Parquet Reader Snap leaking file descriptors (connections to HDFS data nodes). The Open File descriptor values work stable now,
4.11	snapsmrc465	11 Nov 2017	Stable	Added Kerberos support to the standard mode Parquet Reader and Parquet Writer Snaps.
4.10 Patch	hadoop4001	29 Sep 2017	Latest	Supported HDFS Writer to write to the encryption zone.
4.10 Patch	hadoop3887	14 Sep 2017	Latest	Addressed the suggest issue for the HDFS Reader on Hadooplex.
4.10 Patch	hadoop3851	01 Sep 2017	Latest	ORC supports read/write from local file system. Addressed an issue to bind the Hive Metadata to Parquet Writer Schema at Runtime.
4.10 Patch	hadoop3838	23 Aug 2017	Latest	Made HDFS Snaps work with Zone encrypted HDFS.
4.10	snapsmrc414	12 Aug 2017	Stable	Updated the Parquet Writer Snap with Partition by property to support the data written into HDFS based on the partition definition in the schema in Standard mode. Support for S3 accounts with IAM Roles added to Parquet Reader and Parquet Writer HDFS Reader/Writer with Kerberos support on Groundplex (including user impersonation).
4.9 Patch	hadoop3339	25 Jul 2017	Latest	Addressed the following issues: ORC Reader passing, but ORC Writer failing when run on a Cloudplex. ORC Reader Snap is not routing error to error view. Intermittent failures with the ORC Writer
4.9.0 Patch	hadoop3020	22 May 2017	Latest	Added missing dependency org.iq80.snappy:snappy to Hadoop Snap Pack.
4.9	snapsmrc405	13 May 2017	Stable	Upgraded with the latest SnapLogic Platform release.
4.8	snapsmrc398	11 Feb 2017	Stable	Snap-aware error handling policy enabled for Spark mode in Sequence Formatter and Sequence Parser. This ensures the error handling specified on the Snap is used.
4.7.0 Patch	hadoop2343	21 Dec 2016	Latest	Spark Validation: Resolved an issue with validation failing when setting the output file permissions.
4.7	snapsmrc382	23 Nov 2016	Stable	Updated the HDFS Writer and HDFS Reader Snaps with Azure Data Lake account for standard mode pipelines. HDFS Writer: Spark mode support added to write to a specified directory in an Azure Storage Layer using the wasb file system protocol. HDFS Reader: Spark mode support added to read a single file or an HDFS directory from an Azure Storage Layer.
4.6	snapsmrc362	13 Aug 2016	Stable	The following Snaps now support error view in Spark mode: HDFS Reader, Sequence Parser. Resolved an issue in HDFS Writer Snap that sends the same data in output & error view.
4.5	snapsmrc344	18 May 2016	Stable	HDFS Reader and HDFS Writer Snaps updated to support IAM Roles for Amazon EC2. Support for Spark mode added to Parquet Reader, Parquet Writer The HBase Snaps are no longer available as of this release.
4.4.1		18 Mar 2016	Stable	Resolved an issue with Sequence Formatter not working in Spark mode. Resolved an issue with HDFSReader not using the filter set when configuring SparkExec paths.
4.4		13 Feb 2016	Stable	NEW! Parquet Reader and Writer Snaps NEW! ORC Reader and Writer Snaps Spark support added to the HDFS Reader, HDFS Writer, Sequence Formatter, and Sequence Parser Snaps. Behavior change: HDFS Writer in SnapReduce mode now requires the File property to be blank.
4.3.2		15 Jan 2016	Stable	Implemented wasbs:// protocol support in Hadoop Snap Pack. Resolved an issue with HDFS Reader unable to read all files under a folder (including all files under its subfolders) using the ** filter.