Apache Flink Azure ABFS File Sink error (streaming) - UnsupportedFileSystemException: No FileSystem for scheme "file"

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05-10-2024

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Flink Streaming to Azure ABFS: Tackling the "UnsupportedFileSystemException"

The Problem:

You're trying to stream data from an Apache Flink job to an Azure Blob Storage file using the FileSink connector, but you're encountering an error: "UnsupportedFileSystemException: No FileSystem for scheme 'file'". This means Flink can't find the necessary filesystem implementation to access your Azure Blob Storage.

Scenario:

Let's say you're using Flink's DataStream API to process real-time data and want to write it to an Azure Blob Storage container. You've configured your FileSink like this:

DataStream<String> dataStream = ...;

SinkFunction<String> sinkFunction = new FileSink<String>(
    "abfs://[email protected]/path/to/file",
    FileSink.forRowFormat(new SimpleStringEncoder<String>(), new RollingPolicy.DefaultRollingPolicy())
).build();

dataStream.addSink(sinkFunction);

However, when you run your Flink job, you get the dreaded "UnsupportedFileSystemException: No FileSystem for scheme 'file'" error.

Analysis & Solutions:

The error occurs because Flink's FileSink connector, by default, relies on the FileSystem implementations provided by Hadoop. These implementations are designed to work with traditional file systems like HDFS, local file systems, and others. Azure Blob Storage, though accessed via a URI scheme resembling file systems, doesn't use standard Hadoop FileSystem implementations.

Here's how to fix the issue:

1. Include Azure Blob Storage Dependencies:

   Flink doesn't include Azure Blob Storage filesystem implementations by default. You need to add the necessary dependencies to your Flink environment.

   • Maven: Add the following dependency to your project's pom.xml file:

     <dependency>
       <groupId>com.microsoft.azure</groupId>
       <artifactId>azure-storage-blob</artifactId>
       <version>12.16.0</version>
     </dependency>
     

   • Gradle: Add the following dependency to your project's build.gradle file:

     implementation 'com.microsoft.azure:azure-storage-blob:12.16.0'
     

2. Use the AzureBlobFileSystem Class:

   Once you have the Azure Blob Storage dependency, you need to explicitly register the AzureBlobFileSystem class with Flink's FileSystem registry. You can do this using the FileSystem.addFileSystem method.

   // ... your code ...
   
   FileSystem.addFileSystem("abfs", AzureBlobFileSystem.class); 
   
   // ... rest of your Flink code ...
   

   This tells Flink to use the AzureBlobFileSystem class for any URI scheme that starts with "abfs://".

3. Configure Your FileSink:

   Now, you can configure your FileSink to use the AzureBlobFileSystem:

   DataStream<String> dataStream = ...;
   
   SinkFunction<String> sinkFunction = new FileSink<String>(
       "abfs://[email protected]/path/to/file",
       FileSink.forRowFormat(new SimpleStringEncoder<String>(), new RollingPolicy.DefaultRollingPolicy())
   )
   .withFileSystem(new AzureBlobFileSystem()) // Add this line
   .build();
   
   dataStream.addSink(sinkFunction);
   

Key Points:

• Ensure that your Azure Blob Storage account has the necessary permissions for your Flink job to write data.
• Remember to handle any necessary authentication (e.g., SAS tokens) for accessing your Blob Storage account.
• The AzureBlobFileSystem class provides a standard interface for working with Azure Blob Storage, making it easier to integrate with Flink.

Additional Resources:

• Azure Blob Storage Documentation: https://learn.microsoft.com/en-us/azure/storage/blobs/
• Azure Blob Storage Java SDK: https://github.com/Azure/azure-storage-blob
• Apache Flink Documentation: https://flink.apache.org/

Conclusion:

By including the Azure Blob Storage dependency and registering the AzureBlobFileSystem class with Flink, you can overcome the "UnsupportedFileSystemException" and stream data from your Flink jobs to Azure Blob Storage effectively.