HDFS ZipFile Writer
- Lakshmi Manda
- Mohammed Iqbal
- Chandna Mitra
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Overview
Use the HDFS ZipFile Write Snap to read in-coming data and write it to a ZIP file in an HDFS directory. This Snap also enables you to specify file access permissions for the new ZIP file. You can also configure how the Snap handles the new ZIP file if the destination directory already has another ZIP file with the same name.
For the HDFS protocol, use a SnapLogic on-premises Groundplex and ensure that its instance is within the Hadoop cluster and that SSH authentication is established.
The HDFS protocol supported by this Snap is HDFS 2.4.0. This Snap supports both HDFS & ABFS (Azure Data Lake Storage Gen 2 ) protocols.
Expected Input and Output
- Expected Input: Binary data stream containing documents to be written to a ZIP file.
- Expected Output: Zipped file containing the incoming documents.
- Expected Upstream Snaps: Required. Any Snap that offers binary data in its output view. Examples: JSON Formatter, HDFS Reader, File Reader.
- Expected Downstream Snaps: Any Snap that takes document data as input. Examples: Mapper, HDFS Reader.
Prerequisites
The user executing the Snap must have Write permissions on the concerned directory.
Configuring Accounts
This Snap uses account references created on the Accounts page of SnapLogic Manager to handle access to this endpoint. See Configuring Hadoop Accounts for information on setting up this type of account.
Configuring Views
Input | This Snap has at least one document input view. |
|---|---|
| Output | This Snap has at most one document output view. |
| Error | This Snap has at most one document error view. |
Troubleshooting
None at this time.
Limitations and Known Issues
None at this time.
Modes
- Ultra Pipelines: Works in Ultra Pipelines.
Snap Settings
| Label | Required. The name for the Snap. Modify this to be more specific, especially if there are more than one of the same Snap in the pipeline. |
|---|---|
| Directory | The URL for the data source (directory). The Snap supports both HFDS and ABFS(S) protocols. Syntax for a typical HDFS URL: Syntax for a typical ABFS and an ABFSS URL: 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. With the ABFS protocol, SnapLogic creates a temporary file to store the incoming data. Therefore, the hard drive where the JCC is running should have enough space to temporarily store all the account data coming in from ABFS. Default value: [None] |
| File | The relative path and name of the file that must be created post execution. Example:
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. 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
For non-Kerberised clusters, you must activate Superuser access in the Configuration settings.
HDFS Snaps support the following accounts:
When an account is configured with an HDFS Snap, user impersonation settings have no impact on all accounts, except the Kerberos account. |
| File Action | Required. Use this field to specify what you want the Snap to do if the file you want it to create already exists. Available options are: Overwrite, Ignore, and Error.
Default value: Overwrite |
| File Permissions | File permission sets to be assigned to the file. To assign file permissions:
|
| Base directory | Enter here the name of the root directory in the ZIP file. |
| Use input view label | If selected, the input view label is used for all names of the files added to the zip file. Otherwise, the input view ID is used instead, when input the binary stream does not have its content-location in its header. When this option is selected, if there are more than one binary input streams in an input view, for the second input stream and after, the file names will be the input view label appended with '_n'. If the label is in the format of 'name.ext', '_n' will be append to the 'name', e.g. name_2.ext for the second input stream. |
Snap execution | Select one of the three modes in which the Snap executes. Available options are:
|
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.
Examples
Writing and Reading a ZIP File in HDFS
The first part of this example demonstrates how you can use the HDFS ZipFile Write Snap to zip and write a new file into HDFS. The second part of this example demonstrates how you can unzip and check the contents of the newly-created ZIP file.
Click here to download this pipeline. You can also downloaded this pipeline from the Downloads section below.
Create the pipeline as shown below:
The Hadoop Directory Browser Snap
Use a Hadoop Directory Browser Snap to first check the contents of the target directory. This will help you check whether the new file got added to the HDFS directory as expected, later in the example.
Enter the Directory URL as appropriate and specify the File filter as *.zip. This instructs the Snap to list out all the ZIP files in the target directory.
If the Snap executes as expected, you should see the contents of your target directory, as shown below:
Generating a File for Upload
You now need to choose a file to upload into the target directory. You could either select a file directly or use a JSON Generator Snap coupled with a JSON Formatter Snap, as in the example pipeline.
The HDFS ZipFile Writer Snap
Your file is now ready. Configure the HDFS ZipFile Writer Snap to upload the file as a ZIP file into the target directory in HDFS, as shown below.
The Hadoop Directory Browser Snap
Use a Copy Snap to perform two tasks after the ZIP file is created: first, to check whether the new file was created as expected and second, to try and read the contents to the newly-created ZIP file from the target HDFS directory.
To check whether the new file was created, add an HDFS Directory Browser Snap to the pipeline.
If the ZIP file was created, you should see it in the output, as shown below:
HDFS ZipFile Reader
Once you have confirmed that the new ZIP file has been created, use the HDFS ZipFile Reader Snap to read the new ZIP file. If the contents of the new ZIP file is the same as the contents of the input file, you know that the pipeline works!
To read the output of the HDFS ZipFile Read Snap, use a File Reader Snap:
If the contents of the new file is the same as the contents of the original file, you know the example works.
Click here to download this Pipeline. You can also downloaded this pipeline from the Downloads section below.
Downloads
Important steps to successfully reuse Pipelines
- Download and import the pipeline into the SnapLogic application.
- Configure Snap accounts as applicable.
- Provide pipeline parameters as applicable.
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