@startuml
skinparam defaultTextAlignment center
skinparam shadowing false
skinparam sequence {
    MessageAlign center
    ParticipantBackgroundColor Orange
    ParticipantBorderThickness 1
}


participant "node 1\nnode id: A" as A
participant "node 2\n(Target)\nnode id: B" as B
participant "node 3\n(Source)\nnode id: C" as C
participant "node 4\nnode id: D" as D

note over A
Role: **Master**
ConfigEpoch: **2**
CurrentEpoch: **2**

Owner of slot 1200: C

C's configEpoch is 0
end note

/ note over B
Role: **Master**
ConfigEpoch: **1**
CurrentEpoch: **2**

Owner of slot 1200: C

C's configEpoch is 0
end note

/ note over C
Role: **Master**
ConfigEpoch: **0**
CurrentEpoch: **2**

Owner of slot 1200: C
end note

C <- : migrateslots 1200

C -> B: Transfer data for slot 1200

C -> B: End of data transfer

B -> B: Bumping epoch and starting to own slot 1200

note over B
Role: **Master**
<color:red>ConfigEpoch: **3**</color>
<color:red>CurrentEpoch: **3**</color>

<color:red>Owner of slot 1200: B</color>

C's configEpoch is 0
end note

B --> C: PING

C -> C: Purge 1200

note over C
Role: **Master**
ConfigEpoch: **0**
<color:red>CurrentEpoch: **3**</color>

<color:red>Owner of slot 1200: B</color>
end note


== <color:darkgreen>Scale out by adding shard</color> ==


D <-: Start redis

note over D
Role: **Master**
ConfigEpoch: **0**
CurrentEpoch: **0**
end note

D <-: CLUSTER MEET
D -> C: MEET

C -> C: Resolve configEpoch collision

note over C
Role: **Master**
<color:red>ConfigEpoch: **4**</color>
<color:red>CurrentEpoch: **4**</color>

<color:red>Owner of slot 1200: B</color>
end note

C --> D: PONG

note over D
Role: **Master**
ConfigEpoch: **0**
<color:red>CurrentEpoch: **4**</color>
end note

C -> A: PING (My configEpoch is 4)
note over A
Role: **Master**
ConfigEpoch: **2**
<color:red>CurrentEpoch: **4**</color>

Owner of slot 1200: C
(**owner is updated only**
**when someone claims to own it**)

<color:red>C's configEpoch is 4</color>
end note
A --> C: PONG

B -> A: CLUSTER PING\n(My configEpoch is 3, I own 1200)
A --> B: UPDATE\n(C has higher configEpoch and owns 1200)

B -> B: Purge 1200

note over B
Role: **Master**
ConfigEpoch: **3**
<color:red>CurrentEpoch: **4**</color>

<color:red>Owner of slot 1200: C</color>

<color:red>C's configEpoch is 4</color>
end note

== <back:yellow><color:red>No node owns slot 1200</color></back> ==
@enduml