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Importing External Data

There are cases when data is so large, or its processing is organized in such a way, that its preferable to avoid moving it from its current external location. For example data on a network attached storage (NAS), processing data on HDFS, running Dask via SSH, or for a script that streams data from S3 to process it.

External dependencies and external outputs provide ways to track and version data outside of the project.

How external dependencies work

External dependencies will be tracked by DVC, detecting when they change (triggering stage executions on dvc repro, for example).

To define files or directories in an external location as stage dependencies, specify their remote URLs or external paths in dvc.yaml (deps field). Use the same format as the url of certain dvc remote types. Currently, the following supported dvc remote types/protocols:

  • Amazon S3
  • Microsoft Azure Blob Storage
  • Google Cloud Storage
  • SSH
  • HDFS
  • HTTP
  • Local files and directories outside the workspace

Note that remote storage is a different feature.

Examples

Let's take a look at defining and running a download_file stage that simply downloads a file from an external location, on all the supported location types.

See the Remote alias example for info. on using remote locations that require manual authentication setup.

$ dvc run -n download_file \
          -d s3://mybucket/data.txt \
          -o data.txt \
          aws s3 cp s3://mybucket/data.txt data.txt
$ dvc run -n download_file \
          -d azure://mycontainer/data.txt \
          -o data.txt \
          az storage copy \
                     -d data.json \
                     --source-account-name my-account \
                     --source-container mycontainer \
                     --source-blob data.txt
$ dvc run -n download_file \
          -d gs://mybucket/data.txt \
          -o data.txt \
          gsutil cp gs://mybucket/data.txt data.txt
$ dvc run -n download_file \
          -d ssh://user@example.com/path/to/data.txt \
          -o data.txt \
          scp user@example.com:/path/to/data.txt data.txt

⚠️ DVC requires both SSH and SFTP access to work with remote SSH locations. Please check that you are able to connect both ways with tools like ssh and sftp (GNU/Linux).

Note that your server's SFTP root might differ from its physical root (/).

$ dvc run -n download_file \
          -d hdfs://user@example.com/data.txt \
          -o data.txt \
          hdfs fs -copyToLocal \
                  hdfs://user@example.com/data.txt data.txt

Including HTTPs

$ dvc run -n download_file \
          -d https://example.com/data.txt \
          -o data.txt \
          wget https://example.com/data.txt -O data.txt
$ dvc run -n download_file \
          -d /home/shared/data.txt \
          -o data.txt \
          cp /home/shared/data.txt data.txt

Example: Using DVC remote aliases

You may want to encapsulate external locations as configurable entities that can be managed independently. This is useful if the connection requires authentication, if multiple dependencies (or stages) reuse the same location, or if the URL is likely to change in the future.

DVC remotes can do just this. You may use dvc remote add to define them, and then use a special URL with format remote://{remote_name}/{path} (remote alias) to define the external dependency.

Let's see an example using SSH. First, register and configure the remote:

$ dvc remote add myssh ssh://user@example.com
$ dvc remote modify --local myssh password 'mypassword'

Please refer to dvc remote modify for more details like setting up access credentials for the different remote types.

Now, use an alias to this remote when defining the stage:

$ dvc run -n download_file \
          -d remote://myssh/path/to/data.txt \
          -o data.txt \
          wget https://example.com/data.txt -O data.txt

Example: import-url command

In the previous examples, special downloading tools were used: scp, aws s3 cp, etc. dvc import-url simplifies the downloading for all the supported external path or URL types.

$ dvc import-url https://data.dvc.org/get-started/data.xml
Importing 'https://data.dvc.org/get-started/data.xml' -> 'data.xml'

The command above creates the import .dvc file data.xml.dvc, that contains an external dependency (in this case an HTTPs URL).

# ...
deps:
  - etag: '"f432e270cd634c51296ecd2bc2f5e752-5"'
    path: https://data.dvc.org/get-started/data.xml
outs:
  - md5: a304afb96060aad90176268345e10355
    path: data.xml
    cache: true
    persist: false

DVC checks the headers returned by the server, looking for an HTTP ETag or a Content-MD5 header, and uses it to determine whether the source has changed and we need to download the file again.

Example: Imports

dvc import can download a file or directory from any DVC project, or from a Git repository. It also creates an external dependency in its import .dvc file.

$ dvc import git@github.com:iterative/example-get-started model.pkl
Importing 'model.pkl (git@github.com:iterative/example-get-started)'
-> 'model.pkl'

The command above creates model.pkl.dvc, where the external dependency is specified (with the repo field).

# ...
deps:
  - path: model.pkl
    repo:
      url: git@github.com:iterative/example-get-started
      rev_lock: 6c73875a5f5b522f90b5afa9ab12585f64327ca7
outs:
  - md5: 3863d0e317dee0a55c4e59d2ec0eef33
    path: model.pkl
    cache: true

The url and rev_lock subfields under repo are used to save the origin and version of the dependency, respectively.

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