Middleware

The middleware acts as the bridge between the multi-purpose section of the Simulate system and user defined execution environments. It is responsible for managing jobs and cases, as well as all communication with the manager through a well defined API.

It stores the definitions of different cases as well as all currently selected sets of parameter values. As part of this, it is the only service that the front end communicates with to manage jobs. This does mean that there are queries that are sent to the middleware that it does no processing for, and passes directly to the manager. This aspect of the design is intensional and serves to insulate the front end from any need to be aware of user defined components.

The middleware communicates with every component in the defined Simulate system:

Front-end

The middleware is the source of all job and case information for the front end. It has end points to manage cases and jobs, and all job and case management is mediated through the middleware. The middleware does not manage user authentication.

Authenticator:

Many requests supported by the middleware require the user to be authenticated. The middleware uses the authenticator to validate tokens that are passed with requests.

Job Manager:

The manager is responsible for actually running jobs once they have been configured, and for notifying the middleware of changes to their status. Thus, the middleware will send specifications for fully configured jobs to the manager, which will then run them. It will also update the middleware whenever there are changes to the job state. The manager must actively push updates the middleware, as it will not query for changes.

Requirements

The middleware can be run standalone as long as:

1. It has a PostgreSQL instance to store data in
2. You do not try to do anything
3. You can do most tasks with an authenticator
4. For everything else you need a manager

Starting

Set up

In order to run the middleware your system settings must be correctly configured in config.<mode>.json. The mode is set through the FLASK_CONFIGURATION environmental variable, defaulting to dev.

An example configuration is:

{
    "SQLALCHEMY_DATABASE_URI": "postgres://sg:sg@middleware_database/sg",
    "JOB_MANAGER_URL": "http://manager:5010/job",
    "AUTHENTICATION_URL": "http://auth:5050/status",
    "AUTHENTICATE_ROUTES": true
}

Docker

The middleware can be run through docker with the following command:

docker-compose up

Locally

In order to run the middleware locally you must have:

• PostgreSQL
• Python 3.6+

You must then run the following commands:

pip install -r requirements.txt
FLASK_CONFIGURATION=dev python app.py

Note that if you need to run the system in production mode you will need to make the appropriate changes as described in the Flask documentation.