.. SPDX-FileCopyrightText: 2022 James R. Barlow
..
.. SPDX-License-Identifier: CC-BY-SA-4.0

.. _docker:

=====================
OCRmyPDF Docker image
=====================

OCRmyPDF is also available in Docker images that packages recent
versions of all dependencies.

For users who already have Docker installed this may be an easy and
convenient option.

On platforms other than Linux, Docker runs in a virtual machine, and so may
be less performant. You may also want to adjust the Docker virtual machine's
memory and CPU allocation. On Linux, the Docker image runs natively and
performance is comparable to a system installation.

.. _docker-install:

Installing the Docker image
===========================

If you have `Docker <https://docs.docker.com/>`__ installed on your
system, you can install a Docker image of the latest release.

If you can run this command successfully, your system is ready to download and
execute the image:

.. code-block:: bash

   docker run hello-world

.. list-table:: Docker images
   :width: 30 20 50
   :header-rows: 1

   * - Image
     - Architecture
     - Description
   * - ``jbarlow83/ocrmypdf-alpine``
     - x86_64 and arm64
     - Recommended image, based on Alpine Linux.
   * - ``jbarlow83/ocrmypdf-ubuntu``
     - x86_64 and arm64
     - Alternate image, based on Ubuntu. When the Alpine image is considered
       stable and available for arm64, this image will be deprecated.
   * - ``jbarlow83/ocrmypdf``
     - x86_64 and arm64
     - Currently an alias for ocrmypdf-ubuntu. When the Alpine image is
       considered stable and available for arm64, this name point to the
       Alpine image. If you don't about the difference between Alpine and
       Ubuntu, use this image.

To install:

.. code-block:: bash

   docker pull jbarlow83/ocrmypdf-alpine

The ``ocrmypdf`` image is also available, but is deprecated and will be removed
in the future.

OCRmyPDF will use all available CPU cores. See the Docker documentation for
`adjusting memory and CPU on other platforms <https://docs.docker.com/config/containers/resource_constraints/>`__
if you are using Docker on macOS or Windows, where you may need to manually assign
more resources. On Linux, all resources will be available automatically.

The underlying operating system and other details in Docker images are subject
to change at minor releases. If you are modifying the image, you should pin
the version you intend to use.

Using the Docker image on the command line
==========================================

**Unlike typical Docker containers**, in this section the OCRmyPDF Docker
container is ephemeral – it runs for one OCR job and terminates, just like a
command line program. We are using Docker to deliver an application (as opposed
to the more conventional case, where a Docker container runs as a server).
For that reason we usually use the ``--rm`` argument to delete the container
when it exits.

To start a Docker container (instance of the image):

.. code-block:: bash

   docker tag jbarlow83/ocrmypdf-alpine ocrmypdf
   docker run --rm -i ocrmypdf (... all other arguments here...) - -

For convenience, create a shell alias to hide the Docker command. It is
easier to send the input file as stdin and read the output from
stdout – **this avoids the messy permission issues with Docker entirely**.

.. code-block:: bash

   alias docker_ocrmypdf='docker run --rm -i ocrmypdf'
   docker_ocrmypdf --version  # runs docker version
   docker_ocrmypdf - - <input.pdf >output.pdf

Or in the wonderful `fish shell <https://fishshell.com/>`__:

.. code-block:: fish

   alias docker_ocrmypdf 'docker run --rm ocrmypdf'
   funcsave docker_ocrmypdf

Alternately, you could mount the local current working directory as a
Docker volume:

.. code-block:: bash

   alias docker_ocrmypdf='docker run --rm  -i --user "$(id -u):$(id -g)" --workdir /data -v "$PWD:/data" ocrmypdf'
   docker_ocrmypdf /data/input.pdf /data/output.pdf

.. _docker-lang-packs:

Adding languages to the Docker image
====================================

By default the Docker image includes English, German, Simplified Chinese,
French, Portuguese and Spanish, the most popular languages for OCRmyPDF
users based on feedback. You may add other languages by creating a new
Dockerfile based on the public one.

.. code-block:: dockerfile

   FROM jbarlow83/ocrmypdf

   # Example: add Italian
   RUN apt install tesseract-ocr-ita

To install language packs (training data) such as the
`tessdata_best <https://github.com/tesseract-ocr/tessdata_best>`_ suite or
custom data, you first need to determine the version of Tesseract data files, which
may differ from the Tesseract program version. Use this command to determine the data
file version:

.. code-block:: bash

   docker run -i --rm --entrypoint /bin/ls jbarlow83/ocrmypdf /usr/share/tesseract-ocr

As of 2021, the data file version is probably ``4.00``.

You can then add new data with either a Dockerfile:

.. code-block:: dockerfile

   FROM jbarlow83/ocrmypdf:{TAG}

   # Example: add a tessdata_best file
   COPY chi_tra_vert.traineddata /usr/share/tesseract-ocr/<data version>/tessdata/

When creating your own image, you should always pin a specific version of the
OCRmyPDF Docker image. This ensures that your image will not break when a new
version of OCRmyPDF is released.

Alternately, you can copy training data into a Docker container as follows:

.. code-block:: bash

   docker cp mycustomtraining.traineddata name_of_container:/usr/share/tesseract-ocr/<tesseract version>/tessdata/

Extending the Docker image
==========================

You can extend the Docker image with your own customizations, similar to the way
it is extended to add language packs.

Note that the Docker image is subject to change at any time. For example, the base
image may be updated to a newer version of Ubuntu or Debian. Such changes will be
noted in the release notes but might occur at minor versions releases, unless the
way a "casual" user of the Docker image is affected.

If you extend the Docker image, you should pin a specific version of the OCRmyPDF
Docker image.

Executing the test suite
========================

The OCRmyPDF test suite is installed with image. To run it:

.. code-block:: bash

   docker run --rm --entrypoint python  jbarlow83/ocrmypdf -m pytest

Accessing the shell
===================

To use the shell in the Docker image:

.. code-block:: bash

   docker run -it --entrypoint sh  jbarlow83/ocrmypdf

Using the OCRmyPDF web service wrapper
======================================

The OCRmyPDF Docker image includes an example, barebones HTTP web
service. The webservice may be launched as follows:

.. code-block:: bash

   docker run --entrypoint python -p 5000:5000  jbarlow83/ocrmypdf webservice.py

We omit the ``--rm`` parameter so that the container will not be
automatically deleted when it exits.

This will configure the machine to listen on port 5000. On Linux machines
this is port 5000 of localhost. On macOS or Windows machines running
Docker, this is port 5000 of the virtual machine that runs your Docker
images. You can find its IP address using the command ``docker-machine ip``.

Unlike command line usage this program will open a socket and wait for
connections.

.. warning::

   The OCRmyPDF web service wrapper is intended for demonstration or
   development. It provides no security, no authentication, no
   protection against denial of service attacks, and no load balancing.
   The default Flask WSGI server is used, which is intended for
   development only. The server is single-threaded and so can respond to
   only one client at a time. While running OCR, it cannot respond to
   any other clients.

Clients must keep their open connection while waiting for OCR to
complete. This may entail setting a long timeout; this interface is more
useful for internal HTTP API calls.

Unlike the rest of OCRmyPDF, this web service is licensed under the
Affero GPLv3 (AGPLv3) since Ghostscript is also licensed in this way.

In addition to the above, please read our
:ref:`general remarks on using OCRmyPDF as a service <ocr-service>`.
