[SOLR-10515] Persist intermediate trigger state in ZK to continue tracking information across overseer restarts

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 7.0
• Component/s: SolrCloud
• Labels: autoscaling
• Assignee: Andrzej Bialecki
• Reporter: Shalin Shekhar Mangar
• Created: 18/Apr/17 16:35
• Updated: 25/May/17 18:35
• Resolved: 25/May/17 18:35

Description

The current trigger design is simplistic and keeps all the intermediate state in memory. But this presents two problems when the overseer itself fails:

1. We lose tracking state such as which node was added before the overseer restarted
2. A nodeLost trigger can never really fire for the overseer node itself

So we need a way, preferably in the trigger API itself to save intermediate state or checkpoints so that it can seamlessly continue on overseer restarts.