Introduction

Use of a Controller Cluster provides high availability and is a feature subject to the JS7 - License.

• Fail-over is an automated operation that occurs when the Primary Controller is aborted or killed. Fail-over is applied in case of abnormal termination only.
• Switch-over is an operation that is caused by user intervention in JOC Cockpit or by use of the JS7 - REST Web Service API. The procedure includes normal termination of an Active Controller Instance.

For fail-over and switch-over a Cluster Watch Agent is required.

For command line references see the JS7 - Controller - Command Line Operation article.

Cluster Roles

Controller Cluster

The documentation frequently indicates a Primary Controller Instance and a Secondary Controller Instance. The names suggest that one Controller Instance is primarily used and one is for backup purposes.

• The wording in cluster terms suggests to indicate the Active Controller Instance and the Standby Controller Instance independently from the fact if the Primary or Secondary Controller Instance is active.
• A Controller implements an active-passive cluster, however, the term passive is misleading as the Standby Controller Instance is not passive at all but records any state transitions occurring in the Active Controller Instance. Both Controller instances hold a journal of state transitions that is actively synchronized. Fail-over and switch-over will occur only if both Controller instance's journals are in sync.
• The Cluster presents itself as a single unit to the outside world, i.e. to JOC Cockpit and to Agents.
  • Any operations performed in JOC Cockpit are automatically applied to the Active Controller Instance.
  • At any point in time only one Controller instance is active and the other instance is in standby mode.

Cluster Watch Agent

Primary and Secondary Controller instances require a single Agent to be available that acts as an arbitrator in case of fail-over and switch-over.

Cluster Operations

Cluster operations include an automated fail-over and a manual switch-over of the Active Controller Instance.

Fail-over

Fail-over occurs when the Active Controller Instance is terminated abnormally. 

No fail-over occurs when

• the Active Controller Instance is stopped normally from the command line:
  • controller.sh | .cmd stop
• the operating system is shut down and systemd / init.d or a Windows Service are in place to stop the Controller normally.

Fail-over can be invoked by the following actions:

• The Active Controller Instance is killed, for example
  • for Unix with a SIGKILL signal corresponding to the command: kill -9
  • for Windows with the command: taskkill /F
• The operating system crashes.
• In the JS7 - Dashboard the user performs one of the operations: 
  • Active Controller Instance action menu: Abort -> With fail-over
  • Active Controller Instance action menu: Abort and restart -> With fail-over
• From the command line the user performs one of the operations:
  • controller.sh | .cmd abort
  • controller.sh | .cmd kill

Fail-over happens within a short period of time, typically in 2-3s.

Switch-over

Switch-over occurs exclusively when invoked by user intervention.

No switch-over occurs when

• the Active Controller Instance is stopped normally from the command line:
  • controller.sh | .cmd stop
• the operating system is shut down and systemd / init.d or a Windows Service are in place to stop the Controller normally.

Switch-over can be invoked by the following actions:

• In the JS7 - Dashboard the user performs one of the operations: 
  • Active Controller Instance action menu: Abort -> With fail-over
  • Active Controller Instance action menu: Abort and restart -> With fail-over

Switch-over happens within a short period of time, typically in 2-3s.