Clustering

Ignition supports the clustering of two or more gateways together, creating a network of systems that share the same configuration, balance the work of processing client requests, and negotiate the execution of tasks.

Cluster terminology

Node or Peer

A member of the cluster. This is an Ignition Gateway which has clustering enabled and is configured to point to other nodes.

Master

The node currently in charge of the cluster. This node will coordinate other nodes, and is the authority on the current state of the system configuration. It will also execute tasks that can only be run on one node at a time, such as executing transaction groups.

Member

A non-master member of the cluster. Retrieves configuration updates from the master, and handles clients that have been transferred to it.

System configuration in a cluster setting

The system configuration, consisting of projects and settings, is shared across all nodes of the cluster. The master node is the authority, and all nodes who join the cluster will received their configuration from it. The member node's configuration will be overwritten when it joins a cluster, so special care must be taken when setting up clustering between established systems.

Execution of modules in a cluster

Each module will potentially operate differently in a cluster. Some may choose to balance work across the nodes, others will only execute on the master.

Vision module

Clients will be loaded balanced across cluster members. As new clients are launched, they will be transferred to nodes with fewer currently connected clients.

SQL Bridge module

The transaction groups will only be executed by the master.

OPC-UA module

Subscriptions will be monitored across all nodes, but only the master node will communicate with the device, assuming that a clustered connection type is used. If a direct OPC-UA connection is used, each node will communicate with the device.

SQLTags

The tags will be executed independently on all nodes. As mentioned above, if the clustered OPC-UA connection type is used, the data from OPC will be shared across all nodes.

SQLTag Historian

Only the master node will store history to the database.