# 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.

```bash
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.

```dotenv
#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.

```dotenv
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.

```php
$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.

```php
$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](Fast-Ping-Check.md) scheduler is disabled by default.
You can enable it by setting the following:

```php
$config['service_ping_enabled'] = true;
```

## Watchdog

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

```php
$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 to start alerting, polling, discovery and maintenance tasks are no longer required and must be disabled either by removing or commenting them out. The service handles these tasks when enabled. The only cron task enabled after switching to the dispatcher service should be the following:
```
*    *    * * *   librenms    cd /var/www/librenms/ && php artisan schedule:run >> /dev/null 2>&1
```

## 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 /var/www/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 /var/www/librenms/misc/librenms-watchdog.service
/etc/systemd/system/librenms-watchdog.service && systemctl enable --now
librenms-watchdog.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 /var/www/librenms/config.php
# vi /etc/redis.conf
# systemctl enable --now redis.service
# scl enable rh-python36 bash
# change directory to librenms (default /var/www/librenms)
# pip3 install -r requirements.txt
# cp /var/www/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
```
