support leader election for charms

Bug #1258485 reported by John A Meinel
20
This bug affects 4 people
Affects Status Importance Assigned to Milestone
juju-core
Fix Released
High
John A Meinel
cassandra (Juju Charms Collection)
Fix Released
High
Unassigned
postgresql (Juju Charms Collection)
Fix Released
Critical
Unassigned

Bug Description

It is difficult for charms to negotiate amongst each other to decide on a leader. (Unit A may see Units B and C but units B and C do not see eachother)

It should be easy to leverage the central nature of the Juju DB to provide a point of reference for them to collaborate.

The idea is outlined in this doc: https://docs.google.com/document/d/1zDnPK4ZSUI_Je4G2wOThFPqTYVLEJVBVweoSAzIrhHo/edit?pli=1

Marking this as High because we would like to see it in this cycle.

Revision history for this message
Stuart Bishop (stub) wrote :

Not so much difficult, but impossible. The separate sets of units elect different leaders, and you have a split-brain. You can't resolve this without arbitrarily throwing away information from one of the leaders.

Changed in postgresql (Juju Charms Collection):
status: New → Triaged
importance: Undecided → High
importance: High → Critical
Revision history for this message
Stuart Bishop (stub) wrote :

Document the limitation in the PostgreSQL charm. Use the new facilities once they are provided by juju.

JuanJo Ciarlante (jjo)
Changed in cassandra (Juju Charms Collection):
status: New → Triaged
importance: Undecided → High
Curtis Hovey (sinzui)
Changed in juju-core:
importance: High → Medium
Revision history for this message
Curtis Hovey (sinzui) wrote :
Changed in juju-core:
importance: Medium → High
milestone: none → 1.23-beta4
assignee: nobody → John A Meinel (jameinel)
status: Triaged → Fix Committed
Curtis Hovey (sinzui)
Changed in juju-core:
status: Fix Committed → Fix Released
Stuart Bishop (stub)
Changed in cassandra (Juju Charms Collection):
status: Triaged → Fix Released
Changed in postgresql (Juju Charms Collection):
status: Triaged → In Progress
Stuart Bishop (stub)
Changed in postgresql (Juju Charms Collection):
status: In Progress → Fix Released
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