app_simple

Python example for a SemWES application

This is the simplest possible example of a SemWES application service written in Python.

It contains a Python-based SOAP service which exposes a single method called showDialog. This method fits the workflow manager's expectations for a SemWES application and can therefore be registered in the workflow editor. When called, this method delivers a static HTML website which simply contains a button to continue the workflow.

Try it out

The application itself is registered on the CloudiFacturing platform under http://demo/apps/showDialog.owl#showDialog_Service.

An example workflow using this application is registered under http://demo/workflow/Demo_Dialog.owl#Demo_Dialog.

Prerequisites

To build, run, and test this skeleton service, you only need to have Docker installed on your machine. All required software is already bundled in Docker containers.

For further development based on this skeleton, it is highly recommended to use a local Python environment.

Configure, build, and run the service

Configuration

Prior to running the service, have a look at the file env. This file defines environment variables which will be passed into the container. The first one, CONTEXT_ROOT, defines the deployment path of the app relative to root. Essentially, this needs to be set to the relative path under which the VM hosting the service is reachable.

You can define further configuration variables which then can be used in the application source code.

Build and run

To compile service source code, pack it into a Docker container, and run the container, run

./rebuildandrun.sh

The service will listen on port 80 of your machine.

On the first run, this might take a while since the base container images need to be downloaded and dependencies need to be installed. Subsequent builds will complete significantly faster.

This run script starts the container in daemon mode, meaning that the command returns immediately and that logs are not immediately visible.

Alternatively, run the container interactively via:

docker run -p 80:80 --env-file=env calculator

Again, choose a fitting port number.

Testing the service

Once the container is running, it can be tested by using its published wsdl file to create a SOAP webclient and call methods with it.

This example includes a Python-based client application, found in the test_client/ folder. If you have a local Python 3.x environment, you can simply run python test_service.py (make sure that all dependencies defined in requirements.txt) are installed. Alternatively, the example includes a Python Docker container for executing the test client.

To use the Python container, run

cd test_client
./build.sh      # run this only once
./run.sh        # run this every time you want to test

Note that for every run, you will be asked to enter your username, project, and password.

The results of the test will be written into the file test.html, which you can open in any browser. Note that the button on the HTML page will not work, since this test page has not been created from within a running workflow.

You can make changes to test_dialog.py to test other methods or other deployment locations. Rebuilding the container is not necessary after such changes.

Use this example as a template

To use this example as a template for your own service development, simply copy the source code to another location and start editing. To understand the structure of the code, start with main.py and then read Dialog.py.