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

@startuml

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


' === FFWD-UPGRADE PREPARE ===

User -> Mistral : openstack overcloud\nffwd-upgrade prepare
activate Mistral

Mistral -> Mistral : plan update

Mistral -> Heat : stack update
activate Heat

Heat --> Mistral
deactivate Heat

Mistral --> User
deactivate Mistral


' === FFWD-UPGRADE RUN ===

User -> Mistral : openstack overcloud\nffwd-upgrade run
activate Mistral
note right of Heat
    * Operates on all overcloud nodes.
    * Intended usage:
       * On bootstrap nodes it shuts down services and
          performs upgrade to N+1 and N+2.
       * On other nodes it just shuts down services.
end note

Mistral -> Heat : query stack outputs
activate Heat

Heat --> Mistral : stack outputs
deactivate Heat

Mistral -> Mistral : generate playbooks

Mistral -> Ansible : fast_forward_upgrade_playbook.yaml
activate Ansible

Ansible -> Nodes : fast_forward_upgrade_tasks\n(once per each release)
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible -> Nodes : fast_forward_post_upgrade_tasks
activate Nodes

Nodes --> Ansible
deactivate Nodes

Ansible --> Mistral
deactivate Ansible

Mistral --> User :
deactivate Mistral


' === UPGRADE RUN ===

User -> Mistral : openstack overcloud\nupgrade run
activate Mistral
note right of Heat
    * Reuse of the normal upgrade command.
    * Operates on all selected nodes in parallel.
    * Note the separate ansible-playbook invocations:
       facts aren't carried over between playbooks.
    * Intended usage:
      * Upgrades bootstrap nodes from N+2 to N+3.
      * Upgrades other nodes from N to N+3.
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


' === FFWD-UPGRADE CONVERGE ===

User -> Mistral : openstack overcloud\nffwd-upgrade 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