The fe-filesystem module provides a pluggable filesystem abstraction for the Doris FE (Frontend). It decouples the query engine (fe-core) from concrete storage backends (S3, HDFS, Azure Blob, etc.) at both the Maven dependency level and the runtime classpath level.

Each storage backend is a self-contained plugin that is discovered and loaded at FE startup—no modification to fe-core is required to add a new storage backend.

fe-filesystem/                        (aggregator POM — no Java code)
│
├── fe-filesystem-api/                [API]  Core abstractions (FileSystem, Location, …)
├── fe-filesystem-spi/                [SPI]  Provider interface + object-storage contracts
│
├── fe-filesystem-s3/                 [IMPL] AWS S3 / S3-compatible (MinIO, …)
├── fe-filesystem-oss/                [IMPL] Alibaba Cloud OSS  (delegates to S3)
├── fe-filesystem-cos/                [IMPL] Tencent Cloud COS  (delegates to S3)
├── fe-filesystem-obs/                [IMPL] Huawei Cloud OBS   (delegates to S3)
├── fe-filesystem-azure/              [IMPL] Azure Blob Storage
├── fe-filesystem-hdfs/               [IMPL] HDFS / ViewFS / OFS / JFS
├── fe-filesystem-local/              [IMPL] Local filesystem   (testing only)
└── fe-filesystem-broker/             [IMPL] Doris Broker process (Thrift RPC)

• API — Pure-JDK interfaces and value types consumed by fe-core (zero third-party dependencies). Defines FileSystem, Location, FileEntry, DorisInputFile, DorisOutputFile, etc.
• SPI — The FileSystemProvider interface (extends PluginFactory from fe-extension-spi) plus the object-storage layer (ObjStorage, ObjFileSystem, HadoopAuthenticator). Also compiled into fe-core.
• IMPL — Concrete backends. Each one depends on fe-filesystem-spi (and transitively on fe-filesystem-api). S3-delegating backends (OSS, COS, OBS) also depend on fe-filesystem-s3 to reuse S3FileSystem. They must not depend on fe-core, fe-common, or fe-catalog.

At FE startup, Env.initFileSystemPluginManager() creates a FileSystemPluginManager and loads providers in two phases:

1. ServiceLoader scan — Discovers FileSystemProvider implementations already on the classpath (built-in providers, test overrides).
2. Directory plugin scan — Uses DirectoryPluginRuntimeManager to scan the directory configured by Config.filesystem_plugin_root (default: ${DORIS_HOME}/plugins/filesystem). Each direct child directory is treated as an unpacked plugin directory. The runtime manager resolves pluginDir/*.jar (root-level jars, scanned for ServiceLoader registration) and pluginDir/lib/*.jar (dependency jars, available for class loading only).

Classpath providers have higher priority than directory-loaded providers.

When fe-core needs a filesystem, it calls FileSystemFactory.getFileSystem(properties):

Map<String, String> properties
        │
        ▼
FileSystemPluginManager.createFileSystem(properties)
        │
        │  for each registered FileSystemProvider:
        │    1. provider.supports(properties)  ← cheap, no I/O
        │    2. if true → provider.create(properties) → return FileSystem
        │
        ▼
First matching provider wins

Each provider's supports() method examines property keys to decide if it can handle the request. For example:

Each implementation module uses maven-assembly-plugin to produce a zip build artifact. The zip must be unpacked before deployment. At runtime, DirectoryPluginRuntimeManager expects each plugin to be an unpacked directory under filesystem_plugin_root:

${DORIS_HOME}/plugins/filesystem/
├── s3/                                   ← one directory per plugin
│   ├── doris-fe-filesystem-s3.jar        ← plugin jar at root (scanned for ServiceLoader)
│   └── lib/
│       ├── aws-sdk-*.jar                 ← third-party dependencies
│       └── ...
├── hdfs/
│   ├── doris-fe-filesystem-hdfs.jar
│   └── lib/...
└── ...

The Maven build produces a zip with the same layout. To deploy, unzip it into the appropriate subdirectory (e.g., unzip doris-fe-filesystem-s3.zip -d plugins/filesystem/s3/). Dropping the raw .zip file into the directory will not work — DirectoryPluginRuntimeManager resolves pluginDir/*.jar and pluginDir/lib/*.jar from unpacked directories only.

Jars that are already on the fe-core classpath (fe-filesystem-api, fe-filesystem-spi, fe-extension-spi) are excluded from the zip to avoid duplication.

At runtime, DirectoryPluginRuntimeManager creates an isolated ClassLoader per plugin. A ClassLoadingPolicy ensures that shared framework classes (org.apache.doris.filesystem.*, software.amazon.awssdk.*, org.apache.hadoop.*) are loaded parent-first to avoid cross- ClassLoader cast failures.

Several cloud providers (OSS, COS, OBS) are S3-compatible. Instead of duplicating the S3 implementation, they follow a delegation pattern:

1. Translate cloud-native property keys to S3-compatible keys.
2. Extend ObjStorage to override cloud-specific operations (pre-signed URLs, STS tokens).
3. Delegate core I/O to S3FileSystem (from fe-filesystem-s3).

CosFileSystemProvider
  └─→ creates S3FileSystem(CosObjStorage)
        │                     │
        │  FileSystem ops     │  Overrides getPresignedUrl(), getStsToken()
        └─────────────────────┘

┌──────────────────────────────────────────────────────────┐
│                        fe-core                           │
│  Uses: FileSystem, Location, FileEntry (from API)        │
│  Depends on: fe-filesystem-api, fe-filesystem-spi        │
│  Loads plugins from: ${DORIS_HOME}/plugins/filesystem    │
└────────────┬────────────────────────┬────────────────────┘
             │ compile-time           │ runtime (plugin)
             ▼                        ▼
  ┌──────────────────┐    ┌─────────────────────────┐
  │ fe-filesystem-api│    │ fe-filesystem-s3 (zip)  │
  │ fe-filesystem-spi│    │ fe-filesystem-hdfs (zip)│
  │ (compiled in)    │    │ fe-filesystem-xxx (zip) │
  └──────────────────┘    └─────────────────────────┘

• fe-core — Compile-time dependency on fe-filesystem-api and fe-filesystem-spi. Implementation modules are not Maven dependencies of fe-core; they are loaded at runtime from the plugin directory.
• fe-extension-spi — Provides the PluginFactory / Plugin interfaces and the DirectoryPluginRuntimeManager class used by the plugin loading infrastructure.
• fe-filesystem-local — Used in fe-core unit tests (test-scope dependency) so that tests can exercise FileSystem operations without cloud credentials.

Follow these steps to add support for a new storage backend (e.g., Google Cloud Storage):

Create a new directory fe-filesystem/fe-filesystem-gcs/ with this structure:

fe-filesystem-gcs/
├── pom.xml
└── src/
    ├── main/
    │   ├── assembly/
    │   │   └── plugin-zip.xml
    │   ├── java/org/apache/doris/filesystem/gcs/
    │   │   ├── GcsFileSystemProvider.java
    │   │   ├── GcsFileSystem.java
    │   │   └── GcsObjStorage.java          (if object-storage based)
    │   └── resources/META-INF/services/
    │       └── org.apache.doris.filesystem.spi.FileSystemProvider
    └── test/
        └── java/org/apache/doris/filesystem/gcs/
            └── ...Test.java

<project>
    <parent>
        <groupId>org.apache.doris</groupId>
        <artifactId>fe-filesystem</artifactId>
        <version>${revision}</version>
    </parent>

    <artifactId>fe-filesystem-gcs</artifactId>
    <packaging>jar</packaging>
    <name>Doris FE Filesystem - GCS</name>

    <dependencies>
        <!-- REQUIRED: SPI contract (transitively includes API) -->
        <dependency>
            <groupId>org.apache.doris</groupId>
            <artifactId>fe-filesystem-spi</artifactId>
            <version>${revision}</version>
        </dependency>

        <!-- Cloud SDK -->
        <dependency>
            <groupId>com.google.cloud</groupId>
            <artifactId>google-cloud-storage</artifactId>
            <version>...</version>
        </dependency>

        <!-- Test -->
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <finalName>doris-fe-filesystem-gcs</finalName>
        <plugins>
            <!-- Assembly: produces the plugin zip -->
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <configuration>
                    <appendAssemblyId>false</appendAssemblyId>
                    <descriptors>
                        <descriptor>src/main/assembly/plugin-zip.xml</descriptor>
                    </descriptors>
                </configuration>
                <executions>
                    <execution>
                        <id>make-assembly</id>
                        <phase>package</phase>
                        <goals><goal>single</goal></goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

Important: Do not add dependencies on fe-core, fe-common, or fe-catalog.

Copy plugin-zip.xml from an existing module (e.g., fe-filesystem-s3/src/main/assembly/). The key points:

• Place the plugin jar at the root of the zip (for ServiceLoader discovery).
• Place all runtime dependencies in lib/.
• Exclude fe-filesystem-api, fe-filesystem-spi, and fe-extension-spi (they are already on the fe-core classpath).

package org.apache.doris.filesystem.gcs;

import org.apache.doris.filesystem.FileSystem;
import org.apache.doris.filesystem.spi.FileSystemProvider;
import java.io.IOException;
import java.util.Map;

public class GcsFileSystemProvider implements FileSystemProvider {

    // Public no-arg constructor — required by ServiceLoader
    public GcsFileSystemProvider() {}

    @Override
    public boolean supports(Map<String, String> properties) {
        // Must be cheap (no network calls) and deterministic.
        String type = properties.get("_STORAGE_TYPE_");
        return "GCS".equalsIgnoreCase(type);
    }

    @Override
    public FileSystem create(Map<String, String> properties) throws IOException {
        return new GcsFileSystem(properties);
    }

    @Override
    public String name() {
        return "GCS";
    }
}

You have two choices:

• Object-storage backend — Extend ObjFileSystem (from SPI) and implement ObjStorage<C>. This gives you exists(), close(), and cloud-specific delegates for free.
• Custom backend — Implement FileSystem directly (like DFSFileSystem for HDFS).

At minimum, you must implement:

Create the file:

src/main/resources/META-INF/services/org.apache.doris.filesystem.spi.FileSystemProvider

With content:

org.apache.doris.filesystem.gcs.GcsFileSystemProvider

Add your module to fe-filesystem/pom.xml:

<modules>
    ...
    <module>fe-filesystem-gcs</module>
</modules>

• Unit tests — Test your FileSystem and ObjStorage implementations with mocked cloud clients. Place in src/test/java/.
• Environment tests — Tests that require real cloud credentials should be tagged with @Tag("environment"). They are excluded by default and can be enabled with -Dtest.excludedGroups=none.

# Build the new module (must go through the reactor so sibling SNAPSHOTs resolve)
cd fe
mvn package -pl fe-filesystem/fe-filesystem-gcs --also-make -DskipTests

# The build produces a zip at:
#   fe-filesystem/fe-filesystem-gcs/target/doris-fe-filesystem-gcs.zip
# Deploy by unpacking into the plugin directory:
mkdir -p ${DORIS_HOME}/plugins/filesystem/gcs
unzip fe-filesystem/fe-filesystem-gcs/target/doris-fe-filesystem-gcs.zip \
  -d ${DORIS_HOME}/plugins/filesystem/gcs/

# The unpacked layout should be:
#   plugins/filesystem/gcs/
#   ├── doris-fe-filesystem-gcs.jar
#   └── lib/
#       └── *.jar
#
# NOTE: Do NOT drop the .zip file directly — it must be unpacked.

• Module depends only on fe-filesystem-spi (not fe-core/fe-common/fe-catalog)
• FileSystemProvider has a public no-arg constructor
• supports() is cheap — no network calls
• META-INF/services file is present and correct
• Assembly descriptor excludes fe-filesystem-api, fe-filesystem-spi, fe-extension-spi
• Module is listed in fe-filesystem/pom.xml <modules>
• Unit tests pass; environment tests are tagged @Tag("environment")