"How to run the agent" is not limited to a choice between running it either as a cron task (a scheduled task under Windows) or as a daemon (a service under Windows), because this only makes a difference in the control of the execution schedule, ie when the agent runs: in both cases, the server controls the execution plan, ie what the agent does. In order to control this execution plan on agent side, it is also possible to use a different set of executables. The different possibilities, designed as execution modes, are the following:
managed mode: the agent runs continuously in the background, wakes up periodically to execute the tasks required by the server, and may eventually execute out of schedule on server request.
half-managed mode: the agent only runs when launched by a local mechanism (usually an automated scheduling system, such as cron or task scheduler), contacts the servers to ask for a task list, executes them immediately, and stops.
autonomous mode: the agent only runs when launched by a local mechanism, as in previous mode, executes a fixed list of tasks, sends the results to the server, and stops.
This table summarizes who controls what in each mode:
The correct mode to use mainly depends on the role assigned to your GLPI server: is it a trusted management platform, or just a passive information database? In the first case, you'd rather need server-side control, whereas on the second case, you'd rather need agent-side control. But it also depends on your technical expertise: if everything so far sounds like chinese, no need to go further, just select managed mode. Otherwise, the following presents each mode with additional details.
This mode requires the agent to be run as a server process (daemon under Unix, service under Windows). The agent wake-up schedule is controlled from GLPI server, using PROLOG_FREQ setting. More precisely, the agent wakes up at a random time between 50% and 100% of this value, ie for 24H, it will executes sometimes between 12 and 24H. Additionaly, the server may also initiate additional out-of-schedule executions by sending HTTP requests to the agent.
$> fusioninventory-agent --server http://my.server/plugins/fusioninventory/ --daemon
That's the easiest mode to set up, offering (almost) complete control from a centralized point, fully compatible with all available agent features, and the most flexible in terms of usage.
On the downside, this mode involves having a Perl interpreter loaded in memory permanently, which is insignificant on any modern desktop, but may eventually be a concern in specific memory-constraints scenario, such as IoT or minimal virtual machines. It also involves having a privileged process listening on a network port, unless run with no-httpd configuration directive.
And the more important: who controls the GLPI servers also controls all assets where an agent is installed, with ability to execute code at anytime, which may involve running arbitrary command with full privileges if related tasks (currently: deploy) are installed AND enabled on agent side. That's the exact purpose of this mode: everything the GLPI server wants, when the GLPI server wants.
This mode requires a local triggering mechanism to launch the agent. It may be a scheduling system (cron, task scheduler) to run it automatically and regularily, but it may as well be a user session start script, for instance.
$> fusioninventory-agent --server http://my.server/plugins/fusioninventory/
This mode doesn't consume memory permanently, only during agent execution. However, it is also less flexible, as scheduling can't get changed without reconfiguration. But the server still retains control over execution plan, as the agent asks for a task list when run.
This mode is a compromise between the other modes, with the advantages of the autonomous mode in term of resources usage, and the advantages of the managed mode in term of simplicity and flexibility. Its purpose can get summarized as: everything the GLPI server wants, but only when the agent wants.
This mode requires a local triggering mechanism to launch the agent, as the half-managed mode. It also has the same benefits for memory usage and reduced security concerns. However, the agent only executes a fixed list of tasks, and the server only receives the execution results, without any control. As sending those results may be done separatly, this mode may also be used offline. This is achieved by using specific task-dedicated launchers, instead of the fusioninventory-agent one.
Deferred upload example:
$> fusioninventory-inventory > inventory.xml
$> fusioninventory-injector --file inventory.xml --url http://my.server/plugins/fusioninventory/
Immediate upload example:
$> fusioninventory-inventory | curl --data @- http://my.server/plugins/fusioninventory/
This mode is the most complex to set-up, as you have to script the execution of multiple programs, this is not just a matter of configuration. It is also restricted to a limited set of agent tasks, for which a dedicated launcher exists (currently: local inventory, network discovery, network inventory). However, you have a full local control of agent execution.
If you don't trust the GLPI server for any reason (for instance, because it is run by another organization), of if your use case is just to report an inventory regularily, this mode is perfectly suited. It can get summarized as: only what the agent wants, only when the agent wants.
When using managed mode, the server automatically distributes agent executions over time, using random scheduling. However, with other modes, the server doesn't have any control of agent execution schedule, and if they all try to communicate with it simultaneously, for instance because of a cron task executed on all hosts at the same time, the server may get flooded, and become unable to manage the load.
In order to avoid the issue, either distribute automated task execution over
time, or use
--wait command-line option for fusioninventory-agent executable,
introducing a random delay before effective execution. For instance:
# execute agent daily at random time between 0h00 and 0h30
0 0 * * * /usr/bin/fusioninventory-agent --wait=1800
Multiple execution targets¶
Using multiple execution targets (servers or local directories) doesn't mean "execute once, upload the result multiple times", but "tries to execute every available task once for each given target". As a result, there is no guarantee that running an inventory for two different servers, or for one server and for local directory, will produce the exact same result. There is even a known bug on Windows, where the second inventory lacks some specific pieces of information.
The only reliable way currently to produce a single inventory, and transmit the result to multiple targets, is to execute the agent in autonomous mode once, and then upload the results multiple times:
$> fusioninventory-inventory > inventory.xml
$> fusioninventory-injector --file inventory.xml --url http://my.first.server/plugins/fusioninventory/
$> fusioninventory-injector --file inventory.xml --url http://my.second.server/plugins/fusioninventory/