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Dispatcher Service

Status: Release Candidate

The LibreNMS dispatcher service (librenms-service.py) is a new method of running the poller service at set times. It does not replace the php scripts, just the cron entries running them.

External Requirements

A recent version of Python

The LibreNMS service requires Python 3 and some features require behaviour only found in Python3.4+.

Python modules

  • PyMySQL is recommended as it requires no C compiler to install. MySQLclient can also be used, but does require compilation.
  • python-dotenv .env loader
  • redis-py 3.0+ and Redis 5.0+ server (if using distributed polling)
  • psutil

These can be obtained from your OS package manager, or from PyPI with the below commands.

pip3 install -r requirements.txt

Redis (distributed polling)

If you want to use distributed polling, you'll need a Redis instance to coordinate the nodes. It's recommended that you do not share the Redis database with any other system - by default, Redis supports up to 16 databases (numbered 0-15). You can also use Redis on a single host if you want

It's strongly recommended that you deploy a resilient cluster of redis systems, and use redis-sentinel.

You should not rely on the password for the security of your system. See https://redis.io/topics/security

Memcached (distributed polling)

LibreNMS can still use memcached as a locking mechanism when using distributed polling. So you can configure memcached for this purpose unless you have updates disabled.

See Locking Mechanisms at https://docs.librenms.org/Extensions/Distributed-Poller/

MySQL

You should already have this, but the pollers do need access to the SQL database. The LibreNMS service runs faster and more aggressively than the standard poller, so keep an eye on the number of open connections and other important health metrics.

Configuration

Connection settings are required in .env. The .env file is generated after composer install and APP_KEY and NODE_ID are set. Remember that the APP_KEY value must be the same on all your pollers.

#APP_KEY=   #Required, generated by composer install
#NODE_ID=   #Required, generated by composer install

DB_HOST=localhost
DB_DATABASE=librenms
DB_USERNAME=librenms
DB_PASSWORD=

Distributed Polling Configuration

Once you have your Redis database set up, configure it in the .env file on each node. Configure the redis cache driver for distributed locking.

REDIS_HOST=127.0.0.1
REDIS_PORT=6379
# OR
REDIS_SENTINEL=192.0.2.1:26379
REDIS_SENTINEL_SERVICE=myservice

REDIS_DB=0
#REDIS_PASSWORD=
#REDIS_TIMEOUT=60

CACHE_DRIVER=redis

Basic Configuration

Additional configuration settings can be set in config.php or directly into the database.

The defaults are shown here - it's recommended that you at least tune the number of workers.

$config['service_poller_workers']              = 24;     # Processes spawned for polling
$config['service_services_workers']            = 8;      # Processes spawned for service polling
$config['service_discovery_workers']           = 16;     # Processes spawned for discovery


//Optional Settings
$config['service_poller_frequency']            = 300;    # Seconds between polling attempts
$config['service_services_frequency']          = 300;    # Seconds between service polling attempts
$config['service_discovery_frequency']         = 21600;  # Seconds between discovery runs
$config['service_billing_frequency']           = 300;    # Seconds between billing calculations
$config['service_billing_calculate_frequency'] = 60;     # Billing interval
$config['service_poller_down_retry']           = 60;     # Seconds between failed polling attempts
$config['service_loglevel']                    = 'INFO'; # Must be one of 'DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL'
$config['service_update_frequency']            = 86400;  # Seconds between LibreNMS update checks

There are also some SQL options, but these should be inherited from your LibreNMS web UI configuration.

Logs are sent to the system logging service (usually journald or rsyslog) - see https://docs.python.org/3/library/logging.html#logging-levels for the options available.

$config['distributed_poller']                    = true;            # Set to true to enable distributed polling
$config['distributed_poller_name']               = php_uname('n');  # Uniquely identifies the poller instance
$config['distributed_poller_group']              = 0;               # Which group to poll

Tuning the number of workers

See https://your_librenms_install/poller

You want to keep Consumed Worker Seconds comfortably below Maximum Worker Seconds. The closer the values are to each other, the flatter the CPU graph of the poller machine. Meaning that you are utilizing your CPU resources well. As long as Consumed WS stays below Maximum WS and Devices Pending is 0, you should be ok.

If Consumed WS is below Maximum WS and Devices Pending is > 0, your hardware is not up to the task.

Maximum WS equals the number of workers multiplied with the number of seconds in the polling period. (default 300)

Fast Ping

The fast ping scheduler is disabled by default. You can enable it by setting the following:

$config['service_ping_enabled'] = true;

Watchdog

The watchdog scheduler is disabled by default. You can enable it by setting the following:

$config['service_watchdog_enabled'] = true;

The watchdog scheduler will check that the poller log file has been written to within the last poll period. If there is no change to the log file since, the watchdog will restart the polling service. The poller log file is set by $config['log_file'] and defaults to ./logs/librenms.log

Cron Scripts

Once the LibreNMS service is installed, the cron scripts used by LibreNMS are no longer required and must be removed.

Service Installation

A systemd unit file is provided - the sysv and upstart init scripts could also be used with a little modification.

systemd

A systemd unit file can be found in misc/librenms.service. To install run cp /opt/librenms/misc/librenms.service /etc/systemd/system/librenms.service && systemctl enable --now librenms.service

systemd-watchdog

A systemd unit file can be found in misc/librenms-watchdog.service. To install run cp /opt/librenms/misc/librenms-watchdog.service /etc/systemd/system/librenms.service && systemctl enable --now librenms.service

This requires: python3-systemd (or python-systemd on older systems) or https://pypi.org/project/systemd-python/

OS-Specific Instructions

RHEL/CentOS

To get the LibreNMS service running under python3.4+ on RHEL-derivatives with minimal fuss, you can use the software collections build:

First, enable SCL's on your system:

CentOS 7
# yum install centos-release-scl
RHEL 7
# subscription-manager repos --enable rhel-server-rhscl-7-rpms

Then install and configure the runtime and service:

# yum install gcc rh-python36 rh-python36-python-devel epel-release
# yum --enablerepo=remi install redis
# vi /opt/librenms/config.php
# vi /etc/redis.conf
# systemctl enable --now redis.service
# scl enable rh-python36 bash
# change directory to librenms (default /opt/librenms)
# pip3 install -r requirements.txt
# cp /opt/librenms/misc/librenms.service.scl /etc/systemd/system/librenms.service
# systemctl enable --now librenms.service

If you want to use another version of python 3, change rh-python36 in the unit file and the commands above to match the name of the replacement scl.

Debian/Ubuntu

Debian 9 (stretch)

install python3 and python-mysqldb. python-dotenv is not yet available, but the testing package is working fine, you can grab it on https://packages.debian.org/fr/buster/all/python3-dotenv/download (the package may be updated and have a new version number).

apt install python3 python-mysqldb
cd /tmp
wget http://ftp.fr.debian.org/debian/pool/main/p/python-dotenv/python3-dotenv_0.9.1-1_all.deb
dpkg -i python3-dotenv_0.9.1-1_all.deb