@startuml K3s Infrastructure Sequence Diagram
skinparam sequenceMessageAlign center
skinparam responseMessageBelowArrow true

title K3s Kubernetes Cluster Deployment - Sequence Diagram

actor "DevOps Engineer" as client
participant "Terraform CLI" as terraform
participant "K3s Install Module" as module
participant "SSH Connection" as ssh
participant "Server Node" as server
participant "Worker Node 1" as worker1
participant "Worker Node 2" as worker2

== Infrastructure Initialization ==
client -> terraform: terraform init
terraform -> client: Providers initialized

== Deployment Planning ==
client -> terraform: terraform plan
terraform -> module: Parse variables
module -> terraform: Show planned resources
terraform -> client: Display execution plan

== Infrastructure Deployment ==
client -> terraform: terraform apply
terraform -> module: Execute installation

== SSH Configuration ==
module -> module: Create temporary SSH config
note right: Creates secure SSH configuration for all nodes

== Server Provisioning ==
module -> ssh: Establish connection to server
ssh -> server: Connect
module -> server: Install K3s server component
note right
  Uses curl to download K3s installer
  Configures K3s as server node
end note
server --> module: Installation complete

== Kubeconfig Retrieval ==
module -> server: Request kubeconfig
server -> server: Copy k3s.yaml to /tmp
server --> module: Kubeconfig available
module -> module: Download kubeconfig
module -> module: Update server URL in config
note right: Replaces 127.0.0.1 with actual server address

== Node Token Handling ==
module -> server: Request node token
server -> server: Extract node token
server --> module: Node token available
module -> module: Download node token

== Worker Node Provisioning ==
group Worker Node Installation [Parallel execution]
  module -> ssh: Connect to Worker Node 1
  ssh -> worker1: Connect
  module -> worker1: Transfer node token
  module -> worker1: Install K3s agent
  note right
    Installs K3s in agent mode
    Uses token to join the cluster
  end note
  worker1 --> module: Installation complete

  module -> ssh: Connect to Worker Node 2
  ssh -> worker2: Connect
  module -> worker2: Transfer node token
  module -> worker2: Install K3s agent
  worker2 --> module: Installation complete
end

== Completion ==
module --> terraform: All resources provisioned
terraform --> client: Infrastructure deployment complete

== Cluster Usage ==
client -> server: Access Kubernetes via kubeconfig
note right: Uses kubectl with the generated configuration

== Destruction (Optional) ==
client -> terraform: terraform destroy
terraform -> module: Initiate cleanup
module -> worker1: Run agent uninstall script
worker1 --> module: Agent uninstalled
module -> worker2: Run agent uninstall script
worker2 --> module: Agent uninstalled
module -> server: Run server uninstall script
server --> module: Server uninstalled
module --> terraform: All resources cleaned up
terraform --> client: Infrastructure destroyed

footer K3s Infrastructure Sequence Diagram - Version 1.0
@enduml