Project deployment options determine how your project is deployed in a cluster and how it functions at runtime. Set these parameters, including project options, active-active instances, failover intervals, and project deployment type options, in the CCR file manually or within Studio.
To deploy a project in active-active or HA (high availability) mode, set <Project ha="true"> in the CCR file. In an active-active deployment, two instances of a project run simultaneously in a cluster. Active-active projects are typically configured so that the cluster starts the two instances of the project on different nodes (hosts). This feature avoids the risk of a single point of failure at the project level.
One instance of the project is elected as the primary instance. If one of the instances is already active, it is the primary instance. If the failed instance restarts, it assumes the secondary position and maintains this position unless the current instance fails or is stopped.
When a project is deployed in HA (active-active) mode, two instances are created: primary and secondary. Whether the project is in HA mode or not, you can set affinity and cold failover options for each instance, including failover intervals and failure per interval options. Non-HA projects have one instance, numbered 0 (zero). HA project instances are numbered 0 and 1. Some commands require instance numbers to identify instances of a project.
A project fails when it does not run properly or stops running properly. If cold failover is enabled, a failover occurs when a failed project switches to another server to continue processing. Failover typically results in a project restart, though a strong positive affinity to a node that is not available can prevent a project from restarting. Restarts can be limited based on failure intervals and restarts per interval. Failover options, accessed using an instance configuration, include:
Field | Description |
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Failover | Either enabled or disabled. When disabled, project failover restarts are not permitted. When enabled, failure interval and failures per interval fields can be accessed and restarts are permitted. |
Failures per interval | Specifies the number of restarts the project can attempt within a given interval. This count resets to zero if you restart the project manually or if failures are dropped from the list because they are older than the size of the interval. |
Failure interval | (Optional) This specifies the time, in seconds, that makes up an interval. If left blank, the interval time is infinite. |
Field | Description |
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Name | Enter the name of the object of the affinity, that is, the controller name or instance name that the affinity is set for. For instance affinities, the affinity for one instance must refer to the second instance. |
Strength | Specify Strong or weak. Strong requires the project to run on a
specific controller, and no others. If you have strong positive
affinity set for a controller node, and that node fails, the
failover process tries to restart the project on that node. If the
node has not recovered, the project restart fails and you must
restart manually. A weak positive affinity causes the project starts on the preferred controller if possible, but if that controller is unavailable, it may start on another available controller. |
Charge | Specify Positive or negative. If positive, the project runs (for a strong affinity) or prefers to run (for a weak affinity) on the named controller. If negative, the project does not run (or prefers not to run) on the named controller. |