Using Trap Links

Trap links are small text files that reference a single target object in your Amazon S3 storage. With a Trap link, you can save an object in a different location and with a different name without actually duplicating the object. For use cases, see the examples following the configuration instructions.

Limitations:

The target and link file must be accessible with the same storage credentials.
When uploading a link file, Aspera does not check if an object with the trap link file name exists at the destination. For example, if you create the object test and upload a link file .test.asp-trapd-lnk to the same folder, the Aspera client file browser (such as a HST Server GUI) shows two objects with the name test. Any file operations on test are performed on the real object, not the link file.

Configure your Aspera server and create Trap links:

# ssh -i identity_file -p 33001 ec2-user@ec2_host_ip
#  su -

Enable symbolic link support in s3.properties or the docroot.
In s3.properties:Open /opt/aspera/etc/trapd/s3.properties. Locate the following line:
```
#aspera.session.support.symlink = false
```
Uncomment the line and change the value to true:
```
aspera.session.support.symlink = true
```
Save your changes.

In the docroot: Set symbolic link support in the docroot as a query, for example:
```
s3://user1:password@s3.amazonaws.com/path?aspera.session.support.symlink=true
```
Restart Trapd to activate your changes.
```
# systemctl asperatrapd restart
```
Create a trap link file.
On a computer from which you can upload to your object storage, create a text file with a name that follows the format:
.name.asp-trapd-lnk

The file name must start with a dot (.) and end with the asp-trapd-lnk suffix. The name is the object name that is returned when browsing the object storage with an Aspera client; browsing an object store with the storage's default browser, such as AWS Console for S3, shows the link file as is.

The content of the object is the complete path to the target object, including the bucket or container name. The path should not be URL encoded.
Upload the trap link file to the desired location in object storage.

Example 1: Providing a descriptive filename

You have an object in Amazon S3 with the following path:

/mybucket/production/content/29837987350097234987.mpeg

To rename it for your Aspera clients as World-Cup Best-of-day 1.mpeg, create a link file with the following properties:

name: .World-Cup Best-of-day 1.mpeg.asp-trapd.lnk
content: /mybucket/production/content/29837987350097234987.mpeg

Upload the link file to the shared bucket. Now when Aspera clients browse the bucket, they see the World-Cup Best-of-day 1.mpeg object.

Example 2: Accessing content between buckets

You have uploaded a 200 MB file with the following path:

/mybucket/music/album2/200MB

On the client you create a link file with the following properties:

name: .Awesome.mp4.asp-trapd-lnk
content: /mybucket/music/album2/200MB

Upload the link file to the desired location, for example /mybucket/transfer. Now when browsing /mybucket/transfer through the Aspera client, you see a file called Awesome.mp4 that is 200 MB. When you download it, it has the same content as the /mybucket/music/album2/200MB file.

Example 3: Creating a Faspex package with existing files in cloud storage

Using the link file from example 1, .World-Cup Best-of-day 1.mpeg.asp-trapd.lnk, you upload the link file to the Faspex internal storage location. The target file is not copied nor renamed, but when the package is downloaded, the file is received as World-Cup Best-of-day 1.mpeg.