' The png image can be generated by running:
'
'     plantuml minor_update.plantuml

@startuml

actor User
participant Mistral
participant Heat
participant Ansible
participant Nodes
' in newer versions of plantuml we should use: collections Nodes


' === UPDATE PREPARE ===

User -> Mistral : openstack overcloud\nupdate prepare
activate Mistral

Mistral -> Mistral : plan update

Mistral -> Heat : stack update
activate Heat

Heat --> Mistral
deactivate Heat

Mistral --> User
deactivate Mistral


' === UPDATE RUN ===

User -> Mistral : openstack overcloud\nupdate run
activate Mistral
note right of Heat
    * Operates on all selected nodes one-by-one.
end note

Mistral -> Heat : query stack outputs
activate Heat

Heat --> Mistral : stack outputs
deactivate Heat

Mistral -> Mistral : generate playbooks

Mistral -> Ansible : update_steps_playbook.yaml
activate Ansible

Ansible -> Nodes : update_tasks all steps
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible -> Nodes : host_prep_tasks all steps
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible -> Nodes : common_deploy_tasks all steps
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible -> Nodes : post_update_tasks all steps
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible --> Mistral
deactivate Ansible

Mistral --> User :
deactivate Mistral


' === EXTERNAL UPDATE RUN ===

User -> Mistral : openstack overcloud\nexternal-update run
activate Mistral
note right of Heat
    * Executes tasks on undercloud, but can affect
       overcloud via delegation or nested Ansible process.
    * Single play: facts are carried over between
       update and deploy tasks.
    * Often limited via `--tags` to perform a particular
       update task or an update of a particular service.
    * Can be executed before `update run` for some tasks.
end note

Mistral -> Heat : query stack outputs
activate Heat

Heat --> Mistral : stack outputs
deactivate Heat

Mistral -> Mistral : generate playbooks

Mistral -> Ansible : external_update_steps_playbook.yaml
activate Ansible

Ansible -> Nodes : external_update_tasks all steps
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible -> Nodes : external_deploy_tasks all steps
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible --> Mistral
deactivate Ansible

Mistral --> User :
deactivate Mistral


' === UPDATE CONVERGE ===

User -> Mistral : openstack overcloud\nupdate converge
activate Mistral
note right of Heat
    * Essentially the same as `overcloud deploy`,
       asserts that the state of overcloud matches
       the latest templates.
end note

Mistral -> Mistral : plan update

Mistral -> Heat : stack update
activate Heat

Heat --> Mistral
deactivate Heat

Mistral -> Heat : query stack outputs
activate Heat

Heat --> Mistral : stack outputs
deactivate Heat

Mistral -> Mistral : generate playbooks

Mistral -> Ansible : deploy_steps_playbook.yaml
activate Ansible

Ansible -> Nodes : host_prep_tasks
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible -> Nodes : deploy_tasks and external_deploy_tasks\nall steps (interleaved)
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible --> Mistral
deactivate Ansible

Mistral --> User :
deactivate Mistral


@enduml