async_waiter

Python example for an asynchronous service

This is a very simple example of an asynchronous service written in Python. It does nothing but to wait for a specified amount of time, but uses the same concepts and techniques required for wrapping a longer-running calculation in a SemWES asynchronous service.

It also protects all methods by checking that the supplied session token is valid.

For details on the implementation, also read the corresponding tutorial.

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. In SemWES, this path is always made up of two elements:

CONTEXT_ROOT=/<project>-<service_name>

Here, <project> is the project name you log in with, and <service_name> is for you to choose. Please note that <project>-<service_name> must have a maximum length of 32 characters and must consist only of lowercase letters, digits, and hyphens.

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 container 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 only once
./run.sh [start|status]   # run every time you want to test

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

Note that you will have to enter your username, project, and password for each test run in order to obtain a valid session token.

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 Waiter.py.