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

@startuml

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


' === UPGRADE PREPARE ===

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

Mistral -> Mistral : plan update

Mistral -> Heat : stack update
activate Heat

Heat --> Mistral
deactivate Heat

Mistral --> User
deactivate Mistral


' === UPGRADE RUN ===

User -> Mistral : openstack overcloud\nupgrade run
activate Mistral
note right of Heat
    * Operates on all selected nodes in parallel.
    * Note the separate ansible-playbook invocations:
       facts aren't carried over between playbooks.
end note

Mistral -> Heat : query stack outputs
activate Heat

Heat --> Mistral : stack outputs
deactivate Heat

Mistral -> Mistral : generate playbooks

Mistral -> Ansible : upgrade_steps_playbook.yaml
activate Ansible

Ansible -> Nodes : upgrade_tasks all steps
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible --> Mistral
deactivate Ansible

Mistral -> Ansible : deploy_steps_playbook.yaml
activate Ansible

Ansible -> Nodes : host_prep_tasks
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible -> Nodes : deploy_tasks all steps
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible --> Mistral
deactivate Ansible

Mistral -> Ansible : post_upgrade_steps_playbook.yaml
activate Ansible

Ansible -> Nodes : post_upgrade_tasks all steps
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible --> Mistral
deactivate Ansible

Mistral --> User :
deactivate Mistral


' === EXTERNAL UPGRADE RUN ===

User -> Mistral : openstack overcloud\nexternal-upgrade 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
       upgrade and deploy tasks.
    * Often limited via `--tags` to perform a particular
       upgrade task or an upgrade of a particular service.
    * Can be executed before `upgrade 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_upgrade_steps_playbook.yaml
activate Ansible

Ansible -> Nodes : external_upgrade_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


' === UPGRADE CONVERGE ===

User -> Mistral : openstack overcloud\nupgrade 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