Overview¶
A cluster consists of at least three PLOSSYS 5 servers and one management server. The number of PLOSSYS 5 servers has to be odd. The following instructions refer to a cluster containing three PLOSSYS 5 servers.

Requirement¶
All PLOSSYS 5 servers to be connected as a cluster have to be installed identically. For more information about the installation and configuration of a PLOSSYS 5 server, refer to the installation and the configuration of the PLOSSYS 5 server.
Hint - time synchronization
Make sure that the times are synchronous among all PLOSSYS 5 servers in a cluster. Otherwise, the jobs' log data will not be displayed in the correct order.
Scenarios¶
When configuring a cluster, it is important on which PLOSSYS 5 server the instruction is carried out. Below, the PLOSSYS 5 systems are named <server_1>, <server_2> and <server_3>. The mapping of the servers has to be maintained during the complete configuration of the cluster. The following scenarios are distinguished:
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Scenario: Combining three newly installed PLOSSYS 5 servers to a cluster In this case, the names can be mapped to the servers arbitrarily. 
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Scenario: Expanding a PLOSSYS 5 single server to a cluster If a PLOSSYS 5 server has already been running and this is to be expanded to a cluster, the mapping is important: - 
The already existent PLOSSYS 5 server is named <server_1>.
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The two new PLOSSYS 5 servers are named <server_2>and<server_3>. Here, the names can be mapped arbitrarily.
 
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Configure the Cluster¶
In order to run PLOSSYS 5 systems as a cluster, the following parts of the PLOSSYS 5 installation have to be adjusted:
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Logging All PLOSSYS 5 servers in a cluster have to transfer their log data to the same Elasticsearch server. For how to configure the logging in a cluster, refer to Configure the Logging in a Cluster. 
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Consul The Consul processes of all PLOSSYS 5 servers in a cluster have to be connected for cross-server service discovery and system configuration. For how to configure the Consul processes in a cluster, refer to Configure Consul in a Cluster. 
Secure the Cluster¶
For information about how to secure the installation in cluster mode, refer to the following chapters:
For how to secure MongoDB, refer to the SEAL-specific MongoDB documentation.
Next Step¶
Continue with: Configure the Logging in a Cluster