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After EMCO has been installed in a central cluster and some 'edge' clusters have been prepared, this section describes the basic operational sequences that are used to onboard clusters and create and deploy composite applications.

EMCO API

Interaction with the EMCO REST API is primary interface to EMCO.

...

The EMCO REST API is the foundation for the other interaction facilities like the EMCO CLI and EMCO GUI.

EMCO CLI

EMCO has a CLI tool called emcoctl.  More information can be found here: https://github.com/onap/multicloud-k8s/tree/master/src/tools/emcoctl

EMCO GUI

EMCO has a GUI - details:  TBD

EMCO Setup

The EMCO architecture is extensible via the use of controllers which can be used to handle specific placement and configuration (i.e. actions) operations.  The EMCO orchestrator communicates with these controllers via a gRPC interface.  EMCO supports a controller API to allow the administrator to register these controllers with EMCO to provide the necessary connection information (name, port) as well as controller type and relative priority.

...

PlantUML Macro
titleRegister rsync
@startuml
skinparam roundcorner 20
title Register rsync via Controller API

actor Admin

box "Distributed Application Scheduler\n(orchestrator)" #LightBlue
participant Controller_API
participant GRPC_Server_info
participant scheduler
end box

box "Network Configuration Manager\n(ncm)" #LightBlue
participant GRPC_Conns_ncm
participant scheduler_ncm
end box

box "EMCO DB" #LightGreen
database mongo
end box

box "AppContext" #LightGreen
database etcd
end box

box "Resource Synchronizer\n(rsync)" #LightBlue
participant InstallAppAPI
end box

Admin -> Controller_API : POST rsync controller\nregistration information\n(Name:"rsync", Host, Port)
Controller_API -> mongo : Save rsync controller record
Controller_API -> GRPC_Server_info : add a GRPC connection\nto rsync server to\ninternal table
Controller_API -> Admin : Return

== Some time later - ncm\ncalls rsync to instantiate\nNetwork Intents  ==
|||
scheduler_ncm -> etcd : Prepares network intent\nresources in AppContext
scheduler_ncm -> GRPC_Conns_ncm : Retrieve gRPC connection\nto rsync from internal table
GRPC_Conns_ncm -> mongo : if rsync connection not present\nretrieve rsync record\nand create connection
GRPC_Conns_ncm -> scheduler_ncm : return rsync connection
scheduler_ncm -> InstallAppAPI : GRPC InstallApp API call (AppContext identifier)

== Some time later - orchestrator\ncalls rsync to instantiate\nan application ==
|||
scheduler -> etcd : Prepares composite\napplication resources\nin AppContext
scheduler -> GRPC_Server_info : Retrieve gRPC connection\nto rsync from internal table
scheduler -> InstallAppAPI : GRPC InstallApp API call (AppContext identifier)
|||
@enduml

Controller Registration

As mentioned above, EMCO provides for the addition of controllers to perform specific placement and action operations on a Composite Application prior to it being deployed to a set of clusters.

...

PlantUML Macro
titlePlacement and Action Controller Registration
@startuml
skinparam roundcorner 20
title Register placement and action controllers via Controller API

actor Admin

box "Distributed Application Scheduler\n(orchestrator)" #LightBlue
participant Controller_API
participant GRPC_Server_info
participant scheduler
end box

box "EMCO DB" #LightGreen
database mongo
end box

box "AppContext" #LightGreen
database etcd
end box

box "Placement Controller(s)" #LightBlue
participant UpdateContextAPI_place
end box

box "Action Controller(s)" #LightBlue
participant UpdateContextAPI_action
end box

loop for all placement and action controllers
Admin -> Controller_API : POST controller\nregistration information\n(Name, Host, Port, Type, Priority)
Controller_API -> mongo : Save controller record
Controller_API -> GRPC_Server_info : add a GRPC connection\nto controller to\ninternal table
Controller_API -> Admin : Return
end


== Some time later - orchestrator\nis preparing an AppContext\nfor deployment ==
|||
scheduler -> etcd : Prepares initial AppContext\nfor the composite app\nusing the generic\nplacement intents
scheduler -> mongo : Retrieve all controllers\nrequired for this AppContext\ndeployment

loop for all placement controllers in priority order
scheduler -> GRPC_Server_info : Retrieve gRPC connection\nfor controller
scheduler -> UpdateContextAPI_place : GRPC UpdateContext API call (AppContext identifier)
UpdateContextAPI_place -> etcd : updates AppContext according to\nthis controllers placement function
UpdateContextAPI_place -> scheduler : return
end
|||
loop for all action controllers in priority order
scheduler -> GRPC_Server_info : Retrieve gRPC connection\nfor controller
scheduler -> UpdateContextAPI_action : GRPC UpdateContext API call (AppContext identifier)
UpdateContextAPI_action -> etcd : updates AppContext according to\nthis controllers action function
UpdateContextAPI_action -> scheduler : return
end

|||
@enduml

Onboard Clusters

Clusters are onboarded to EMCO by first creating a Cluster Provider and then adding Clusters to the Cluster Provider.

...

PlantUML Macro
titleCluster Onboarding
@startuml
skinparam roundcorner 20
title Onboard clusters

actor Admin

box "Cluster Manager\n(clm)" #LightBlue
participant Cluster_API
participant Cluster_Module
end box

box "Distributed Application Scheduler\n(orchestrator)" #LightBlue
participant Controller_API
participant GRPC_Server_info
participant scheduler
end box

box "EMCO DB" #LightGreen
database mongo
end box

box "AppContext" #LightGreen
database etcd
end box

box "Resource Synchronizer\n(rsync)" #LightBlue
participant rsync
end box

box "Edge Cluster"
participant K8S_API
end box


Admin -> Cluster_API ++ : POST cluster_provider (name)
Cluster_API -> Cluster_Module ++ : call create cluster\nprovider handler
Cluster_Module -> mongo : Save cluster provider record
Cluster_Module -> Cluster_API -- : return
Cluster_API -> Admin -- : return

Admin -> Cluster_API ++ : POST cluster (name, kubeconfig file)
Cluster_API -> Cluster_Module ++ : call create cluster\nhandler
Cluster_Module -> mongo : Save cluster record
Cluster_Module -> Cluster_API -- : return
Cluster_API -> Admin -- : return

Admin -> Cluster_API ++ : POST label(s) or kvpair(s) (optionally)
Cluster_API -> Cluster_Module ++ : call create cluster label\nor kv pair handler
Cluster_Module -> mongo : Save cluster label or\nkv pair record
Cluster_Module -> Cluster_API -- : return
Cluster_API -> Admin -- : return


== Some time later - generic placement controller\nis preparing an AppContext\nfor deployment ==
|||
scheduler -> Cluster_Module ++ : GET clusters by label (or name)
Cluster_Module -> mongo : retrieve cluster records by label
Cluster_Module -> scheduler -- : return
loop for all resources in a cluster
scheduler -> etcd : Create cluster key(s)\nin AppContext and add\nappropriate resources
end

== Some time later - rsync is\ndeploying resources to a cluster ==
|||
loop for all clusters in a composite application
rsync -> rsync : get k8s client for cluster
rsync -> Cluster_Module ++ : if no k8s client, GET kubeconfig for cluster
Cluster_Module -> mongo : retrieve cluster kubeconfig
Cluster_Module -> rsync -- : return
rsync -> rsync : create k8s client with kubeconfig
loop for all resources in a cluster
rsync -> K8S_API : apply resource to cluster
end
end

|||
@enduml


Create Network Intents

(show how network intents are defined and deployed to clusters)

Create Composite Application

(show how composite applications are prepared along with the intents required to deploy them)

Basic Composite Application Lifecycle

(show instantiate, terminate, status operations of a composite application)