Symbolic Links
Similar to a Windows shortcut, a symbolic link improves flexibility in resource management and simplifies access to objects. You can create a symbolic link that points to another object. By clicking the link, you access the target object. Symbolic links are useful in the following scenarios:
- Object migration: When an object's storage path changes, you may want clients to continue using the old path without updating code. A symbolic link provides a smooth transition and prevents service interruptions. For example, if a file moves from old-path/file.txt to new-path/file.txt, you can create a symbolic link at old-path/file.txt that points to new-path/file.txt. Clients can still access the file through old-path/file.txt.
- Flexible access paths: You can create multiple symbolic links for the same file to provide different access paths without duplicating data. This reduces storage costs and simplifies file management.
- Seamless file updates: Updating a file by overwriting it may cause brief unavailability or require complex switchover logic. A symbolic link enables a seamless transition. For example, if the original file is data/file.txt and the updated file is data/new-file.txt, you can create a symbolic link data/file.txt that points to data/new-file.txt. Clients continue to access the latest content through data/file.txt without changing service logic.
- Simplified access to deep paths: Long or complex object paths are hard to remember. A short symbolic link provides a simple entry point to objects stored in deep or nested paths.
Constraints
This feature is supported only in certain regions (for example, CN East2). Refer to the console for the latest support status.
| Category | Constraint |
|---|---|
| Functions |
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| Others |
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Important Notes
- ETag of a symbolic link is calculated based on the name of the target object.
- A symbolic link can be in the Standard, Infrequent Access, Archive, or Deep Archive storage class. Symbolic links do not need to be restored. If you attempt to restore a symbolic link, error 405 is reported, with a message OperationNotSupported. However, if the target object of a symbolic link is in the Archive or Deep Archive storage class, you must restore the target object before you can download (GetObject) it through the symbolic link.
- Symbolic links are included in a bucket inventory. During bucket storage statistics collection, symbolic links are treated the same as common objects. The size of a symbolic link is the length of the target object name.
- When a symbolic link is replicated to another bucket, and that bucket contains an object with the same name as the target object in the source bucket, the replicated symbolic link can access the target object in the destination bucket.
- The metadata of a symbolic link is independent of that of the target object. For example, you can specify the Content-Type header when creating a symbolic link or by calling the API for modifying object metadata after the symbolic link is created. If Content-Type is not specified, the system sets it to binary/octet-stream for a symbolic link by default.
Required Permissions
| Operation | Required Permission |
|---|---|
| Creating a symbolic link | Requires the PutObject permission. When you create a symbolic link, the system does not check whether you have permission to access the target object. |
| Accessing the target object through a symbolic link | Performed through the HeadObject or GetObject API. The access permission for symbolic links follows the principle of least privilege. You must have the GetObject permission for both the symbolic link and the target object. |
| Obtaining information about a symbolic link | Performed through the GetSymlink API and requires the GetObject permission. |
| Copying a symbolic link | Requires the GetObject and PutObject permissions. Replication does not support modification, which means that the target object to which the symbolic link points cannot be changed through headers. |
| Deleting a symbolic link | Requires the DeleteObject permission. Deleting a symbolic link and deleting its target object are independent operations. |
You are advised to use IAM or bucket policies for authorization. For details, see OBS Access Control Overview, Using IAM Custom Policies, or Configuring an Object Policy.
Interaction with Versioning
Versioning disabled:
- When you create a symbolic link with the same name as an existing symbolic link in the same path, the new link overwrites the existing one.
- When you create a symbolic link with the same name as an existing common object (not a symbolic link) in the same path, the common object is overwritten by the symbolic link.
Versioning enabled:
- When you create a symbolic link with the same name as an existing symbolic link in the same path, the new link becomes the current version. The existing link becomes a historical version.
- When you create a symbolic link with the same name as an existing common object (not a symbolic link) in the same path, the common object becomes a historical version.
- After versioning is enabled for a bucket, symbolic links can have multiple versions. Each version has a unique version ID. Both current and historical versions can point to the same target object. If the target object also has multiple versions, a symbolic link can point only to the latest version of the target object. It cannot point to any historical versions.
Operations Related to Symbolic Links
Using OBS Console
- In the navigation pane of OBS Console, choose Buckets.
- In the bucket list, click the desired bucket. The Objects page is displayed.
- Locate the target object and click Create Symbolic Link in the Operation column.
- In the displayed dialog box, enter the symbolic link information and click OK.
When specifying the symbolic link path, follow the rules shown on the page. Assume your object is in the /file/ directory.
- If you select an absolute path and name it linktest1, the symbolic link path is /linktest1.
- If you select the current path and name it linktest2, the symbolic link path is /file/linktest2.
Figure 2 Creating a symbolic link
If you create a symbolic link (for example, myfile) without an extension for a file that has an extension (for example, myfile.jpg), you may encounter the following situations when accessing or downloading the file:
- The file can be previewed through the management console or a URL.
- The file cannot be opened after download. When you download the file, the system uses the symbolic link name (myfile) as the saved file name by default. Because the name does not include the .jpg extension, the operating system cannot identify the file type or determine which application to use. The file typically marked as an unknown file. To open it, add the correct file extension manually.
- After the configuration is complete, the symbolic link appears in the object list.
marks a symbolic link. You can click the symbolic link name to view its details. Figure 3 Symbolic link file
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