marathon-event-bus-client

   

A generic client to listen to Marathon's (Server Sent) Event Bus.

Usage

Install as a dependency like this:

``bash
npm install marathon-event-bus-client --save
`

Events

$3

As of the Marathon sources there are currently the following events:

* pod_created_event
* pod_updated_event
* pod_deleted_event
* scheduler_registered_event
* scheduler_reregistered_event
* scheduler_disconnected_event
* subscribe_event
* unsubscribe_event
* event_stream_attached
* event_stream_detached
* add_health_check_event
* remove_health_check_event
* failed_health_check_event
* health_status_changed_event
* unhealthy_task_kill_event
* group_change_success
* group_change_failed
* deployment_info
* deployment_success
* deployment_failed
* deployment_step_success
* deployment_step_failure
* app_terminated_event
* status_update_event
* instance_changed_event
* unknown_instance_terminated_event
* instance_health_changed_event
* framework_message_event

$3

The Marathon Event Bus Client itself emits the following events:

* subscribed: Is emitted after a successful subscription to the Marathon Event Bus.
* unsubscribed: Is emitted after unsubscribe() is called.
* error: Is emitted in case of internal or upstream errors.

Using the client

$3

You can specify the following properties when instantiating the Marathon Event Bus Client:

* marathonHost: The Marathon base URL. Default is master.mesos.
* marathonPort: The Marathon port. Default is 8080.
* marathonProtocol: The Marathon protocol (http or https). Default is http.
* marathonUri: The relative path where the Marathon Event Bus endpoint can be found. Default is /v2/events.
* marathonHeaders: A dict of http headers which should be added to Marathon's API requests , mainly for authentication/authorization (both Authorization and Content-Type are allowed). See the Marathon docs or the DC/OS docs for further info. Not used by default.
* eventTypes: An array of event types emitted by Marathon (see above for a list). Default is ["deployment_info", "deployment_success", "deployment_failed"].
* handlers: A map object consisting of handler functions for the individual Marathon events. See below for an explanation. No defaults.

$3

The Marathon Event Bus Client only exposes the subscribe() and the unsubscribe() methods. You can catch all above events via on(, function (data) { ... }.

$3

The custom event handler functions can be configured by setting a map object as handlers property during the instantiation. Each map object's property represents a event handling function. The property name needs to match on of the Marathon event types from the list of known Marathon events.

This is an example handlers map object:

`javascript
{ // Specify the custom event handlers
"deployment_info": function (name, data) {
console.log("We have a new deployment info!");
},
"deployment_success": function (name, data) {
console.log("Our deployment was successful!");
}
}
`

The function arguments are:

* name: The name of the emitted event
* data: The emitted data for the event

$3

For a complete example, have a look at examples/example.js. Also, for a "real-life example", you can refer to marathon-slack.

`javascript
// Use the MarathonEventBusClient
const MarathonEventBusClient = require("marathon-event-bus-client");

// Define relevant event types
const eventTypes = ["deployment_info", "deployment_success", "deployment_failed"];

// Create MarathonEventBusClient instance
const mebc = new MarathonEventBusClient({
marathonHost: "localhost", // Use SSE test server
eventTypes: eventTypes,
marathonHeaders: { // When using the Marathon Event Bus outside the cluster, otherwise just omit the marathonHeaders.
"Authorization": "token=" // Replace with a real authentication token
},
handlers: { // Specify the custom event handlers
"deployment_info": function (name, data) {
console.log("Custom handler for " + name);
// Send information of the "deployment_info" event to an external service (here: Just an echo service)
request("https://echo.getpostman.com/get?name=" + name + "&startTime=" + data.timestamp, function (error, response, body) {
body = JSON.parse(body);
if (!error && response.statusCode == 200) {
console.log("Here's the data we have just sent to the echo service:");
console.log("--------------------");
console.log(JSON.stringify(body.args)); // Show the sent data
console.log("--------------------");
}
});
},
"deployment_success": function (name, data) {
console.log("Custom handler for " + name);
}
}
});

// Wait for "connected" event
mebc.on("connected", function () {

console.log("Subscribed to the Marathon Event Bus");

// For example purposes: Log all events we receive
// In real-world usage, you should define what needs to be done when
// receiving specific events in the handlers property for each event type
eventTypes.forEach(function (eventType) {
mebc.on(eventType, function (data) {
console.log("Caught '" + eventType + "' event!");
});
});

// Shutdown after 30 seconds
setTimeout(function () {
console.log("Shutting down");
// Unsubscribe from Event Bus
mebc.unsubscribe();
}, 30000);

});

// Wait for "unsubscribed" event
mebc.on("unsubscribed", function () {
console.log("Unsubscribed from the Marathon Event Bus");
});

// Catch error events
mebc.on("error", function (errorObj) {
console.log("Got an error on " + errorObj.timestamp + ":");
console.log(JSON.stringify(errorObj.error));
});

// Subscribe to Marathon Event Bus
mebc.subscribe();
``