18. RDFox Docker Images¶

This section documents the official Docker images for RDFox which are publicly available from Docker Hub repository oxfordsemantic/rdfox, and their companion images in repository oxfordsemantic/rdfox-init.

The defaults of the RDFox Docker images are described in the next section, followed by a section describing suggested approaches for mounting the RDFox license key, server directory and shell root directory. The final section provides a selection of example docker run commands for running the images. The only pre-requisite for running these is a Docker installation for your platform. See the official Docker installation page for instructions.

The documentation assumes familiarity with the basics of Docker in general and in particular the different ways of mounting storage into containers with the desired container-side permissions.

Note

For readability, short-form (-v) mount arguments will be used throughout but readers should be aware that the official Docker documentation recommends the long-form (--mount) alternative.

18.1. Image Defaults¶

Default values for the images in the oxfordsemantic/rdfox repository are described below. It is possible to override all of these defaults but, for simplicity, the documentation of each assumes the other defaults are being used.

User: The default user within the images is rdfox. This determines the default server directory path within containers as /home/rdfox/.RDFox.
Entrypoint: The default entry point for the images is the RDFox executable embedded at container path /opt/RDFox/RDFox. The version of the executable at this path will match the version in the tag for the image.
Command: The default command is daemon request-logger elf. This can be overridden with any valid RDFox command (see Section 16.1).
Working directory: The default working directory for the images is /data. This has no impact when starting in daemon mode but will be the default root directory when using the RDFox shell.
Ports: The images expose the default port for the RDFox endpoint: 12110.
Required superuser capabilities: In the interests of security, images in the oxfordsemantic/rdfox repository have been designed to run with no superuser capabilities (see Linux kernel capabilities). The inclusion of the argument --cap-drop ALL in docker run commands, or the equivalent in other environments, is recommended when launching images in the above repository.

18.2. Suggested Mounts¶

The following sections provide suggestions on how to mount the license key, how to mount and initialize storage for the server directory and how to mount storage for the shell root directory.

18.2.1. Mounting the License Key¶

Although various solutions to injecting the RDFox license key are possible, the recommended approach is to mount a valid, in-date license key file to container path /opt/RDFox/RDFox.lic. This will enable the containerized RDFox process to locate the license without requiring additional command line arguments whilst ensuring that the license key need not be stored within the server directory.

If using the images in Kubernetes, where the RDFox license key may be held as a Secret resource, mounting the secret as described above will hide the image’s entry-point executable, leading to a failure to start. In this situation, mapping the secret into the container’s environment via variable RDFOX_LICENSE_CONTENT is the next most convenient option.

The methods described above work for both oxfordsemantic/rdfox and oxfordsemantic/rdfox-init images.

18.2.2. Mounting the Server Directory¶

When RDFox is configured to persist roles and data stores, it does so inside the configured server directory. As described above, the default server directory path for oxfordsemantic/rdfox images is /home/rdfox/.RDFox. For use cases where persistence is enabled it is therefore most convenient to mount storage, whether a host directory or Docker volume, to that container path. If for any reason the server directory must be mounted to a different container path, the default command for the image must be overridden with a valid RDFox command which includes the -server-directory parameter to specify the path to the server directory within the container.

Wherever the storage is mounted, it must be readable and writable by the user that launches RDFox within the container (the rdfox user by default). In order to start RDFox in daemon mode without having to supply a role name and password, it is also necessary that users have previously initialized access control within the server directory (see Section 11.2.1 for more information about initialization). The companion images described in the next section can help to prepare new server directories in order to meet all of these requirements.

18.2.2.1. Initializing the Server Directory with a Companion Image¶

To simplify the initialization of new server directories, each image in the oxfordsemantic/rdfox repository, has a companion image with the same tag in the oxfordsemantic/rdfox-init repository (for example, the image oxfordsemantic/rdfox:4.1.0 has companion oxfordsemantic/rdfox-init:4.1.0). These images ensure that the mounted storage is readable and writable by the rdfox user, and also run RDFox to initialize persistence of access control. Additionally, users can specify an RDFox shell script to run as part of the initialization by mounting it with name initialize.rdfox in the container’s working directory (/data by default). This makes it possible to create and populate one or more data stores or to configure access control as part of the server directory initialization, avoiding the need to do so via the REST endpoint later on. If an initialize.rdfox script is found within the process’s working directory, it is executed under the continue-if-exists error handling policy (see Section 16.2.5).

Companion images accept the following subset of RDFox’s supported command line parameters:

-api-log {on|off}
-api-log.directory <api-log-directory>
-api-log.input-recording-limit <recording-limit>
-license-content <license-content>
-license-file <license-file>
-password <role-password>
-persist-ds {off|file}
-role <role-name>
-server-directory <server-directory>

The RDFox command line parameters not accepted by companion images are irrelevant for initializing server directories and specifying them, or any unrecognized parameters, will cause the container to exit before taking any action.

See below for an example Docker run command for a companion image.

Note

In order to change the ownership of the mounted storage and then run RDFox as the right user, companion images must be started as root (their default user) with capabilities CAP_CHOWN, CAP_SETUID and CAP_SETGID.

18.2.3. Mounting the Shell Root Directory¶

Often, when developing applications for RDFox it is convenient to keep the rules, base facts and shell scripts for the application in a single directory. When using the RDFox shell in Docker, this directory must be mounted into the container’s file system with the appropriate permissions to allow the rdfox user to read and write as necessary.

Users are free to use either a named volume or a bind mount for the shell root directory. Bind mounting a host directory will often be more convenient for this purpose however named volumes offer more flexibility to achieve the necessary container-side permissions, particularly where the Docker client is on Windows. The most convenient target path for the mount is the default working directory /data as this is the default value for the shell root variable.

18.3. Example Docker Run Commands¶

The example commands in this section demonstrate how to run RDFox Docker images in several different configurations, starting with the simplest possible and progressing to more realistic scenarios. With the appropriate substitutions, the commands should work on any operating system where the Docker CLI is supported.

In all of the examples, <path-to-license-file> should be replaced with an absolute path to a valid, in-date RDFox license key file.

Example: Running Interactively with no Persistence or Endpoint.

The simplest possible docker run command to launch RDFox in a container is:

docker run -it -v <path-to-license-file>:/opt/RDFox/RDFox.lic oxfordsemantic/rdfox sandbox

This will start the RDFox shell for interactive usage but is not very useful. First of all, nothing from the session will be persisted since no server directory has been mounted and the image default daemon command has been overridden with sandbox mode which disables role and data store persistence by default. Second, since no storage has been mounted to the /data path, there is no possibility of importing from or exporting to the host filesystem using the shell, and we have no access to any shell scripts. Finally, since we did not publish the 12110 port it will be impossible to reach the RDFox endpoint from outside the container even if it is started using endpoint start. Nevertheless, this command may be useful for quickly testing out RDFox functionality on data and rules simple enough to be typed (or pasted) in.

Example: Initializing a New Server Directory.

The following command creates a Docker volume with name rdfox-server-directory (assuming no such volume exists already) and uses the latest oxfordsemantic/rdfox-init image to prepare it for use with the latest oxfordsemantic/rdfox image. Access control will be initialized with the role name and password held in the environment variables RDFOX_ROLE and RDFOX_PASSWORD respectively (these must be set in the environment where the command is run).

docker run --rm -v <path-to-license-file>:/opt/RDFox/RDFox.lic \
           -v rdfox-server-directory:/home/rdfox/.RDFox \
           -e RDFOX_ROLE \
           -e RDFOX_PASSWORD \
           oxfordsemantic/rdfox-init

If the resulting container exits cleanly, the rdfox-server-directory volume will be ready for use, as demonstrated in the next example.

Example: Running in Daemon Mode With Persistence

Using volume <rdfox-server-directory>, prepared as described in the preceding example, a containerized RDFox daemon, reachable at host port <host-port>, can be launched using the following command:

docker run -d --cap-drop ALL -p <host-port>:12110 \
           -v <path-to-license-file>:/opt/RDFox/RDFox.lic \
           -v <rdfox-server-directory>:/home/rdfox/.RDFox \
           oxfordsemantic/rdfox

Example: Running Interactively With Persistence

To run interactively users must include the -i and -t arguments to docker run and override the default daemon command with shell as in the following command.

docker run -it --cap-drop ALL \
           -v <path-to-license-file>:/opt/RDFox/RDFox.lic \
           -v <rdfox-server-directory>:/home/rdfox/.RDFox \
           -v <shell-root-directory>:/data \
           oxfordsemantic/rdfox shell

When launched this way, RDFox will always prompt for a role name and password which it will use to initialize access control if <rdfox-server-directory> has not previously been initialized, and in all cases to log into the shell.

Example: Running in Daemon Mode With No Persistence

To run as a purely in-memory data store, where all interaction will be via the RDFox endpoint, it is possible to supply the name and password of the first role via environment variables in order to initialize access control without any interaction via standard input and output. Assuming variables RDFOX_ROLE and RDFOX_PASSWORD have been defined in the environment where the command will run, a containerized RDFox daemon with no persistence, reachable at host port <host-port>, can be launched using the following command:

docker run -d --cap-drop ALL \
           -p <host-port>:12110 \
           -v <path-to-license-file>:/opt/RDFox/RDFox.lic \
           -e RDFOX_ROLE \
           -e RDFOX_PASSWORD \
           oxfordsemantic/rdfox \
           -persist-roles off -persist-ds off daemon

The RDFox server started by the above command will contain no data stores initially. These can be created and populated via the REST API however, in some situations, it may be desirable to do this at startup time using an RDFox shell script. Given a startup script start.rdfox in host directory <shell-root-directory>, a containerized RDFox daemon with no persistence, initialized by the script and reachable at host port <host-port>, can be launched using the following command:

docker run -d --cap-drop ALL \
           -p <host-port>:12110 \
           -v <path-to-license-file>:/opt/RDFox/RDFox.lic \
           -v <shell-root-directory>:/data \
           -e RDFOX_ROLE \
           -e RDFOX_PASSWORD \
           oxfordsemantic/rdfox -persist-roles off -persist-ds off shell . start

To prevent RDFox from exiting after executing the shell script, and to ensure that the endpoint is running, the script should conclude with the daemon command (see Section 16.2.2.10).

18.4. Checking the Health of RDFox Containers¶

Many container orchestration systems require a health check endpoint to determine whether a container is healthy. The RDFox endpoint has a dedicated API for this purpose at path /health. GET requests to this path will always return 204 - No Content. See also Section 14.14.