Zoom is a platform created by Spot Trading to manage real-time application startup, configuration and dependency management. Zoom provides a server-side agent and front-end web interface to allow for easy administration of our software infrastructure.

The Zoom agent is python service called Sentinel. It is responsible for watching the status of Linux daemons and Windows services. When the service it is watching is running, the agent creates a node in ZooKeeper.

All interaction with Sentinel happens in ZooKeeper:

• Configuration: hosted as xml text within a node in ZooKeeper. The Agent will automatically restart upon a configuration change.
• Commands to underlying daemons: To send a 'restart' to the daemon being monitored, we created a node in ZooKeeper with JSON data inside.

The Web Front-end (which we simply call Zoom) is completely abstracted from the agents. This means that the agents will still run as they are configured to without the Zoom web server running. Zoom is more a means for humans to get involved should they need to start/stop an application, change the configuration of an agent, etc.

Zoom's web front-end is powered by Tornado Web's Tornado web server. Our web interface was designed using Twitter's Bootstrap framework. In implementing Zoom's front-end, we used a handful of open-source JavaScript libraries. We simplified the inclusion and handling of these modules using jrburke's RequireJS library. To support real-time updates to Zoom's web portal, we used the Sammy.js, Knockout, and jQuery libraries. We implemented dependency visualization using mbostock's D3.js library, and we provide users with formatted XML in our sentinel configuration tool using vkiryukhin's elegant vkBeautify formatter.

The concept behind the whole project is that certain applications require specific resources in order to start correctly. App1 may need App2 to be running, for example. We manage this complexity by representing every application as a node in ZooKeeper. We then set watches (A ZooKeeper concept) on the nodes each application requires. When these nodes are created or destroyed, the watch triggers a callback within the agent. In this manner, applications will not start until they are ready to, and will do so automatically.

It's assumed that you are familiar with Apache's ZooKeeper and the basics of administering it. Lots of useful information regarding ZooKeeper can be found in the ZooKeeper Administrator's Guide.

To use Zoom, you must have Python installed. For your convenience, we have provided a bootstrap.sh file in sentinel/agent/scripts/ which uses Python's easy_install module to include the python-ldap, tornado, kazoo, setproctitle, requests, and pyodbc Python packages.

Why are we open-sourcing? Read about at Spot's engineering blog here.