====== Multi instance ======

  * Several Pro.Monitor instances can work together to distribute monitoring workload. 
  * The instance with central server role will manage the configuration and distribute tasks to the ones with agent role. 
  * A central server can also act as an agent. 
  * A standalone Pro.Monitor instance will therefore be a central server and an agent.
  * Communication between Server and agents is **Unidirectionnal**: Only agents will initiate connection to the Server.
  * The Server doesn't require any inbound connection to the agent's network.
  * The server can therefore be publicly accessible while the agents can be in protected area: **No need for SSL tunnel, VPN or complex network settings** to deploy a mutli-instance implementation and centrally manage the monitoring of multiple isolated environments.
  * This architecture can also be used to add more **robustness**, by having several monitoring agents and be **resilient** in case one goes down.

===== Role settings =====

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  * In the Role section, you can configure:
    * **Central server role :** If active, the instance will centrally manage monitoring configuration
    * **Agent:** If active, the instance will execute monitoring tasks (connect to systems, detect problems, generate metrics and alerts)
    * **Central server URL:** The server to bind to.
    * **Download and install a certificate**
      * Simply click on "Download and install a self-signed certificate" button and Pro.Monitor will perform all necessary operation to have the job done !
      * **Be aware of the following :**
        * Default certificate will not work in Multi-instance mode, agents will refuse the connection because the certificate is not bound to server IP address
        * In this case, you must generate a self signed certificate and bind it to the local IP
        * Generated certificates will be stored in the keystore
        * Pro.Monitor keystore is located in the ''certificates/.keystore'' file of Pro.Monitor install folder
        * **ATTENTION :** Any change in security settings will be effective only after restarting Pro.Monitor

==== Standalone server role ====

  * This is the **default mode**, no specific configuration is required.
  * Central server and agent roles are both enabled. In this mode, Pro.Monitor is an agent and a server at the same time.
  * The server will manage the configuration, user interface and execute monitoring tasks.
  * Every Pro.Monitor instance with an enabled agent has a **local agent** used to execute monitoring tasks.
  * The agent will appear automatically in the list of accepted agents and cannot be deleted.

**NOTE:** In standalone mode, it is not necessary to assign groups to the local agent. But if you do so, unassigned groups won't be monitored.

==== Central server role ====

  * In this mode, Pro.Monitor will manage the configuration of the monitoring and distribute tasks to one or several remote agents.
  * It will be used as monitoring portal for the users and also hold the database, and connect to the plugins.
  * **Central server role** must be active in the Multi-instance tab
  * Central server URL, including scheme and port number must be registered in the **Central server URL** field of each agent
  * Each agent bound to the server must be accepted once by the admin
  * Associations between groups and agents must be done via the Agents groups tab.
  * One group can be managed by several agents, in that case, group workload will be distributed across each compatible agent.
  * Some system settings from central server will be propagated automatically to each agent:
    * ''Number of parallel tasks''
    * ''Monitoring process timeout''
    * ''Log level and duration''
  * Most others like ''Monitoring process memory'' will still be local settings
  * If the **Agent role** is enabled, the local agent will be used as any remote agents.

**NOTE:** You can visualize agent activities in the **Monitor statistics** menu (Must activate monitors results retention in System tab)

==== Agent role ====

  * In Multi-instance tab, activate **Agent** mode and deactivate **Central server role**
  * Define the agent name to use
  * Set the primary server URL
  * Save the settings. The agent will connect to the primary server and will be handled from there.
  * Some local settings will still remain available, such as ''System->monitoring processes memory'' or ''log retention''
  * **Connecting to central server in HTTPS**:
    * Server must use an certificate generated for its actual IP (will not work will the default certificate)
    * Download server certificate using your browser and add it in the Pro.Monitor keystore of the agent (see **[[https|HTTPS config]]** for more details)

**NOTE:**
  * If the instance was previously used as a server, its configuration will be hidden until switched back to its server role.
  * The Agent doesn't require any licence

===== Failover =====

  Failover allows to implement high availability for a Pro.Monitor server

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  * To implement high availability, one Pro.Monitor instance must be set as **PRIMARY** and another one as **SECONDARY**
  * Url of the PRIMARY must be registered in the SECONDARY
  * Instance UUID of the SECONDARY must be set in the PRIMARY
  * PRIMARY must be set to **ACTIVE** mode
  * SECONDARY must be set to **STANDBY** mode

Once set the following will happen:
  * The SECONDARY will regularly poll the PRIMARY and refresh its configuration if anything changed on the PRIMARY.
  * The SECONDARY will switch to ACTIVE mode to replace the PRIMARY in two cases:
    * If the SECONDARY cannot reach the PRIMARY after a timeout.
    * If the PRIMARY indicates an inconsistent state to the SECONDARY

To revert from a failover:
  * If the PRIMARY becomes online again, the SECONDARY **will not** switch to STANDBY automatically
  * You have to manually set the SECONDARY to STANDBY. **DO NOT SWITCH PRIMARY TO ACTIVE** I must become active automatically
  * If SECONDARY is in STANDBY mode, the PRIMARY will automatically switch to ACTIVE

By default, the failover mode is set to **OFF**, use this mode to deactivate the failover mechanism.