scads is an API server for smallish semi-structured data objects such as configurations, profiles, etc The initial implementation supports only 'workflow' objects used by the HandBag tool: https://github.com/MITLibraries/handbag It is basically a RESTful API server (JSON only) intended to support client tools and UIs. It was written expressly to be run on Google AppEngine, and makes extensive use of its PaaS environment and services. Currently the service is a prototype, lacking basic features such as authentication, but they could be added easily in future.

The service exposes only 2 endpoints for use in Handbag contexts (admin UIs, the desktop tool):

A GET request will return a list of all workflow URIs on the server. If the query parameter 'agent' is supplied, only those associated with the named agent will be returned:

http://mitlib-scads.appspot.com/workflows?agent=helen

A POST to this URI with a JSON representation of a workflow will add it to the server, observing the following rule: if the name of the posted workflow matches any existing one on the server it will be considered a new version of that workflow, otherwise it will be considered a new workflow. Versions have special behavior associated with them, viz. all suitably configured agents will be 'upgraded' to this version, and will no longer have access to previous versions. The version number will be automatically set to one higher than the highest currently on the server for that workflow. New workflows, however, have no agent impact at all.

A PUT to this URI with a JSON representation of an agent will create or update the set of workflows associated with the agent. The agent is implicitly created by this PUT, and does not need to have pre-existed on the server. There is no direct way to purge an agent once defined, but one could effectively deactivate an agent by PUTing the JSON:

{
  "id": "jeremy",
  "name": "jeremy",
  "workflows": []
}

Normally, the "workflows" list would contain some real workflow ids: [324098234098, 234290348920, 2342938423]

A GET request with a query parameter correctly identifying a workflow will return a JSON representation of it:

http://mitlib-scads.appspot.comm/workflow?id=4645645754

A DELETE request with a query parameter correctly identifying a workflow will cause the workflow to be removed from the server. All agent associations with the workflow will also be eliminated, without installing any replacement workflow - e.g. an earlier version - for the agent.

Like most PaaS services, AppEngine has push-button deployment. The AppEngine SDK includes a tool to easily manage the process. In the directory above where this code is installed ('scads'), simply run:

appcfg.py update scads/

The service will automatically create a new version of the runtime while retaining the previous one in case a roll-back becomes necessary. Remember to rename the application (in app.yaml) since GAE requires globally unique application names.

When test coverage and other production-related build processes are added, the app can be configured to deploy directly from travis CI, so merging a GitHub PR can lead to immediately updated code on the server.