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Architectures

Warning: For Commercial Edition customers, please get in touch with your Centreon Sales representative or Technical Account Manager before implementing this. Extensions needs a specific license files to smoothly work on both nodes.

2-nodes cluster

Presentation

The architecture of the high availability platform is composed by these 4 roles:

• centreon-central-master: Centreon web GUI, active in nominal mode
• centreon-central-slave: Centreon web GUI, passive in nominal mode
• quorum-device: third server allowing to reach a majority of votes to elect a master
• poller: server hosting a distant poller (the quorum-device role can be held by a poller

Note: One will notice that at least 3 servers are needed whereas the title mentions only two nodes. There is no mistake here, there are indeed 2 central nodes, and the monitoring role must rely on external pollers, not on central servers.

Cluster services description

There are three types of services:

• centreon and centreon_storage MariaDB databases
• Centreon RRD Broker and PHP7, that can run on both nodes at the same time
• Centreon Engine, Centreon Central Broker, Apache, Centcore/Gorgone, etc. processes, that must run on one node only

MariaDB data is hosted by both centreon-central-master and centreon-central-slave servers. Depending on the state of the resources of the cluster, one has the "master" role (regardless of the server's name) the second is named "slave" and synchronizes asynchronously (MariaDB process) the databases from the "master" server.

Services are running on either the centreon-central-master server or on the centreon-central-slave server depending on the state of the resource group.

The server with the quorum-device role does not host any particular service. It aims to obtain an absolute majority in a vote of the cluster master.

Centreon main components

Monitoring poller components

A monitoring poller provides:

• a monitoring scheduler Centreon Engine (centengine)
• an event handler Centreon Broker Module (cbmod) that allows centengine to connect to the active central server to transfer the collected data

Note: cbmod is configured to connect to the Centreon VIP.

Centreon main server components

A Centreon central server provides:

• a monitoring scheduler Centreon Engine (centengine)

• an event handler (cbmod) that connects locally to transfer the collected data

• a centralized events management process (cbd_central-broker) that:

  • inserts into the database the information collected
  • transfers in local performance data in order to generate graphs

• a performance data management process (cbd-central-rrd) to create/update the performance graphs (RRD files)

• a web Centreon interface (Apache/PHP7)

Note: The Centreon RRD broker process is active on both Centreon central servers in order to avoid having to synchronize the directories hosting the RRD files (via DRBD for example). It is powered by a dual-output from cbd_central_broker process directed to both centreon-central-master's and central-centreon-slave's RRD broker processes.

Database components

Centreon database components are:

• centreon: monitoring configuration database
• centreon_storage: monitoring information (live and history) database

The databases hosted by centreon-central-master and centreon-central-slave are synchronized using MariaDB replication process.

Overall schema

Description of the cluster resources

The cluster services are divided into two functional groups.

MariaDB functional group

The ms_mysql functional group is a "multi-state" resource. This resource can be in master mode on one node and in slave mode on another node. The ms_mysql-master meta-resource is assigned to the replication master.

Centreon functional group

The centreon functional group gathers all Centreon resources to manage them.

Resources type description

All these resources are described in the table below.

Name	Type	Description
ms_mysql	multi-state resource	Handles mysql process and the data replication
ms_mysql-master	location	Set MariaDB Master server rule preference
php7	clone service	FastCGI Process Manager service (rh-php72-php-fpm)
cbd_rrd	clone service	Broker RRD service (cbd)
centreon	group	Centreon "primitive services" group
vip	primitive service	VIP address for centreon
http	primitive service	Apache service (httpd24-httpd)
gorgone	primitive service	Gorgone service (gorgoned)
centreon_central_sync	primitive service	Files synchronization service
cbd_central_broker	primitive service	Central Broker service (cbd-sql)
centengine	primitive service	Centreon-Engine service (centengine)
centreontrapd	primitive service	SNMP Traps management service (centreontrapd)
snmptrapd	primitive service	SNMP Traps listening service (snmptrapd)

Note: The resources of the centreon group are started one after the other in the list order.

Recommendations

Number of nodes

Centreon recommends using at least 3 servers for highly available Centreon platform. While it is possible to split database and central roles, for now we only suggest deploying two standalone "central & DB" servers.

Role of the Centreon central server

In the case of a failover architecture the Centreon central cluster must not be used as a poller. In other words, it mustn't monitor resources. Its monitoring ability should only be used to monitor its pollers. If this recommendation is not followed, the centengine service would take too long to restart and it may cause the functional centreon group to failover.

VIP usage

Centreon recommends using VIP address to access the Web User Interface and the database as well.

Constraints

The failover architecture implies various constraints:

• Synchronization (via rsync) of:

  • Media files
  • Configuration files for: centengine, cbd_central_broker, cbd_rrd
  • Centreon-MBI reports hosted on the Web server

• MariaDB files ibdata* and ib_logfile* must be in the "datadir" directory or in a subdirectory (scripts centreondb-smooth-backup.sh and mysql-sync-bigdb.sh aren't compatible with this operation);

• MariaDB files log-bin* and relay-log* can be located in a directory (or a subdirectory) different from "datadir". They can also be on a different logical volume (lvm) than "datadir". However, the logical volume must be located in the volume group where "datadir" is stored.