vilicus is a system designed to monitor and alert to problems with network infrastructure and hosts. For example it can notify when a process is no longer running, or monitor the CPU utilisation of a machine and alert if it is sustained above a threshold.

It can be compared to bigger tools such as Nagios and NetXMS, but on a far smaller scale.

It supports Android push notifications via the Pushover service.

• check: a check is a configured object to monitor, such as a running process or a CPU threshold.

• server: the netmon server runs with a database backend and exposes an API for agents to contact and report on configured checks.

• agent: an agent runs on each host to be monitored and reports back to the server with details of its configured checks.

Each agent is completely stateless, getting most of its configuration and all of its configured checks from the server at statup. This means its footprint is tiny and requires only minimal dependencies.

Here is a simplified diagram of how the system works;

                               +--------+   4. server sends notifications if needed   +-----------------+
  /--------------------------> | server | ------------------------------------------> | email to admins |
  |                            +--------+                                             +-----------------+
  |                                |
  |                                | 1. agent contacts server and
  |                                |    and downloads list of all
  | 3. agent submits result        |    configured checks for itself
  |    of checks to server         |
  |    and "checks in",        +-------+   2. agent runs checks      +---------------------+
  |    meaning it has          | agent | <-------------------------> | is process running? |
  |    completed its checks    +-------+                             +---------------------+
  |                                |
  |                                |
  |                                |
   \-------------------------------/

Communication between agents and server is done via REST requests. Since it uses HTTP, an agent and the server can be on the same machine, on the same network, or across the Internet. An agent simply requires HTTP access over port 80 to the server. A sample of the interaction between agent and server is given below:

  GET /api/v1/agent/
    ^ fetch the agent object (this also verifies access)

  GET /api/v1/process_check/
    ^ get a list of this agent's process checks

  POST /api/v1/check_history/
  POST /api/v1/check_history/
  POST /api/v1/check_history/
    ^ post the results back to the server, one for each check (3 are configured)

  PUT /api/v1/agent/1/
    ^ checkout - signal to the server the agent has finished its checks for this run

The server never contacts any of its agents, rather each agent contacts the server as it is assumed to be at a fixed address.

• Server: see requirements.txt