User Guide


Passive Monitoring

NetEye’s passive monitoring abilities count on Tornado, a Complex Event Processor that receives reports of events from data sources such as monitoring, email, and telegram, matches them against pre-configured rules, and executes the actions associated with those rules, which can include sending notifications, logging to files, and annotating events in a time series graphing system.

Tornado is a high performance, scalable application, and is intended to handle millions of events each second on standard server hardware. Its overall architecture is depicted in Fig. 146.

Tornado architecture

Fig. 146 Tornado architecture

Tornado Architecture

Tornado is structured as a library, with three example binaries included that show how it can be used. The three main components of the Tornado architecture are:

  • The Tornado Collector(s), or just Collector(s)

  • The Tornado Engine, or Engine

  • The Tornado Executor(s), or Executor(s)*

The term Tornado refers to the whole project or to a deployed system that includes all three components.

Along with the main components, the following concepts are fundamental to the Tornado architecture:

  • An Action: An operation performed by Tornado, usually on an external system. For example, writing to Elastic Search or setting a state in a monitoring system.

  • A Tornado (or Internal) Event: The Tornado-specific Event format.

  • A Datasource: A system that sends External Events to Tornado, or a system to which Tornado subscribes to receive External Events.

  • An External Event: An input received from a datasource, whose format depends on its source. An example of input are events collected from rsyslog.

  • A Rule: A group of conditions that an Internal Event must match to trigger a set of Actions.

See also

Events and Actions are described in more detail in the Tornado common API documentation.

Architecturally, Tornado is organized as a processing pipeline, where input events move from collectors to the engine, to executors, without branching or returning.

When the system receives an External Event, it first arrives at a Collector where it is converted into a Tornado Event. Then it is forwarded to the Tornado Engine where it is matched against user-defined, composable Rules. Finally, generated Actions are dispatched to the Executors.

The Tornado pipeline:

Datasources (e.g. rsyslog)
  | External Events
  \-> Tornado Collectors
        | Tornado (or Internal) Events
        \-> Tornado Engine (matches based on Rules)
              | Actions
              \-> Tornado Executors (execute the Actions)

Tornado Interaction with Icinga 2

The interaction between Tornado and Icinga 2 is explained in details in sections Icinga 2 Executor and Smart Monitoring Check Result Executor. In particular the Smart Monitoring Executor interacts with Icinga 2 to create objects and set their statuses. To ensure that the status of the Icinga 2 objects does not get lost, NetEye provides an automatism that stops the execution of Smart Monitoring Actions during any Icinga 2 restart or Icinga Director deployment.

The automatism keeps track of all Icinga 2 restarts (we consider also Icinga Director deployments as Icinga 2 restarts) in the icinga2_restarts table of the director database. As soon as an Icinga 2 restart takes place, a new entry with PENDING status is added in that table and at the same time the Tornado Smart Monitoring Executor is deactivated via API.

The icinga-director.service unit monitors the status of the Icinga 2 restarts that are in PENDING status and sets them to FINISHED as soon as the service recognizes that Icinga 2 completed the restart, then the Tornado Smart Monitoring Executor is activated.

Icinga 2 (including Icinga Director deployments) can not restart if for any reason there is another restart PENDING, i.e., ongoing or stuck, which in some corner case may result in Icinga 2 restarts being blocked. Should you encounter such unfortunate situation, you can manually unblock new restarts by issuing the following command, which will set the status of all PENDING restarts to OBSOLETE (i.e., restarts that are outdated):

neteye# icingacli director icinga2restart resetlock


The purpose of a Collector is to receive and convert external events into the internal Tornado Event structure, and forward them to the Tornado Engine.

Collectors are Datasource-specific. For each datasource, there must be at least one collector that knows how to manipulate the datasource’s Events and generate Tornado Events.

Out of the box, Tornado provides a number of Collectors for handling inputs from snmptrapd, rsyslog, JSON from Nats channels and generic Webhooks.

Because all Collectors are defined with a simple format, Collectors for new event types can easily be added or extended from existing types for:

  • Monitoring events

  • Email messages

  • Telegram

  • DNS

  • Cloud monitoring (AWS, Azure, Cisco/Meraki, etc.)

  • Netflow

  • Elastic Stack

  • SMS

  • Operating system and authorization events


The Engine is the second step of the pipeline. It receives and processes the events produced by the Collectors. The outcome of this step is fully defined by a processing tree composed of Filters and Rule Sets.

A Filter is a processing node that defines an access condition on the children nodes.

A Rule Set is a node that contains an ordered set of Rules, where each Rule determines:

  • The conditions a Tornado Event has to respect to match it

  • The actions to be executed in case of a match

The processing tree is parsed at startup from a configuration folder where the node definitions are stored in JSON format.

When an event matches one or more Rules, the Engine produces a set of Actions and forwards them to one or more Executors.


The Executors are the last element in the Tornado pipeline. They receive the Actions produced from the Engine and trigger the associated executable instructions.

An Action can be any command, process or operation. For example it can include:

  • Forwarding the events to a monitoring system

  • Logging events locally (e.g., as processed, discarded or matched) or remotely

  • Archiving events using software such as the Elastic Stack

  • Invoking a custom shell script

A single Executor usually takes care of a single Action type.

Tornado License

Tornado is licensed under the Apache License, Version 2.0 or the MIT license, at your choice. All files in the project carrying such notice may not be copied, modified, or distributed except according to those terms.