Understanding JIRA Events

JIRA Event is a message that issue sends to all JIRA background processed when a change on the issue is performed. Event, once fired, can be processed by multiple background processes (called listeners) such as email sending listener or SLA listener.

Any change performed on an JIRA issue creates a corresponding issue event. E.g. if you create an issue, Issue Created event is fired. JIRA mechanism in dependent on the issue events. They inform the system that something has happened and trigger appropriate actions within JIRA.

The two types of issue events in JIRA are: 

• System events that are fired by JIRA internally. They cannot be changed or deleted but can be used by workflow designers outside of standard actions.
   Tip: On the Atlassian Documentation Space you can read that events can be inactivated.  But regardless event activity status it can be used in SLA Behaviours.

• Custom events - are defined by system administrators and used in workflow transitions.

Events are generally send in two major situations:

• Issue Actions - standard issues action such as editing or commenting without executing any workflow transition. Event for the Actions cannot be changed (e.g. adding new comment always fires event called "Issue Commented" and changing issue's assignee through  "Assign" button always fires event "Issue Assigned".
• Workflow Transitions - each workflow transition fires an event. When you design your workflow you have to set it up (usuwally it's the very last post function in each transition) or use standard event proposed by JIRA. Normally JIRA proposed "Issue Created" event for Create transition and "Generic Event" for all other. We strongly recommend using you own transition for each event especially in large JIRA instances (due to possible performance improvements).