Low-Level Orchestrator

Introduction

The aerOS Low-level Orchestrator receives formal services implementation blueprints from the HLO and translates this blueprints into running services in the selected IEs.

Features

In aerOS, the LLOs are based on the K8s Operator Pattern, which provide a framework to automatically control the lifecycle management of resources. This does not mean that LLOs only support the management of K8s workloads, but that actually leverage this widely used and tested resource management framework to finally reflect the desired state of services (to be deployed in a certain IE), with a common way to express the Implementation Blueprints (custom K8s Custom Resources) that is independent on the container management framework used in the selected IE, so that agnostic for the HLO. Moreover, using K8s Operators allows to easily extend the aerOS LLO to cover more container management frameworks without being decoupled from the entire orchestration solution.

It is important to highligh that several LLOs may exist in a domain, one for each container management framework that run the IEs of the domain. Therefore, the LLO Operator developed to interact with an specific container management framework (Docker for instance) contains the needed logic to run and delete the containerized workload in the selected IE of the same domain.

Custom Resource Definition

In K8s, Custom Resources (CR) are extensions to the Kubernetes API. In aerOS, a common structure for all the Custom Resources used by the LLO Operators has been defined to cover all the Implementation Blueprint regardless of the underlying container management framework of the selected IE to deploy a service. This means that the only field of the CR that will change depending on the container management framework is the kind. For instance, for Docker it will be ServiceComponentDocker and for K8s it will be ServiceComponentK8s.

As an example, when a K8s CR of type ServiceComponentK8s is deployed in the K8s cluster in which has been installed the LLO Operators, the LLO Operator for IEs with K8s as container management framework is triggered to deploy the container in the selected IE, which in this case is a K8s node. The same process occurs when the selected IE is a standalone Docker machine.

This is an example of a LLO Custom Resource:

apiVersion: llo.aeros-project.eu/v1alpha1
kind: <It_Depends_On_The_Container_Management_Framework>
metadata:
  labels:
    app.kubernetes.io/name: component-3-of-the-service-1
    app.kubernetes.io/instance: urn_ngsi-ld_Service_1_Component_3
    app.kubernetes.io/part-of: urn_ngsi-ld_Service_1
    app.kubernetes.io/managed-by: aeros-project.eu
    app.kubernetes.io/created-by: urn_ngsi-ld_LowLevelOrchestrator_2
  name: service-component-sample
spec:
  selectedIE:
    id: urn:ngsi-ld:InfrastructureElement:CloudFerro:4073c6a5a93b
    hostname: continuum-cluster-worker-1
  image: your_public_container_image:tag
  cliArgs:
    - key: -test
    - key: -testValue
      value: id3
  envVars:
    - key: SAMPLE_ENV_VAR
      value: sampleValue
  exposePorts: true
  ports:
    - number: 80
      protocol: TCP
    - number: 3000
      protocol: UDP
  networkOverlay:
    internalIp: 10.13.0.4/32
    dns: 10.13.0.1
    privateKey: WBFL8CnjwnyLkV9+Hk/u/iXGuB3C38i5AMTDlyD8wWC=
    publicKey: k8hAPelei4z1wBfyJO5cDUJutyuW10kOh5ezeh7p7TE=
    endpoint: ncsrd-mvp-domain.aeros-project.eu:51820
    allowedIps: 10.13.0.0/24

LLO types

According to the aerOS architecture and as mentioned in the above section, the IEs of the continuum can run different types of container management frameworks, such as K8s, Docker or containerd. Thus, a different K8s Operator must be developed to support the required containerization technologies run by the IEs. Currently, aerOS provides support for these container management frameworks:

• LLO K8s
• LLO Docker

In the future, a guide will be provided in order to assist on the development of new LLO types.

LLO Operator API

A custom REST API has been developed to help end users to manage the aerOS K8s Custom Resources deployed in the K8s clusters.

Method	Endpoint	Description	Query parameters	Payload	Response format
GET	/version	Returns the API version			{“version”: “1.0.1-mvp”,”supportedCRs”: list of supported CRs}
GET	/health	Returns the health status			{“message”: “Health status”}
GET	/v1/service-components	Retrieves all the deployed Service Components	type: type of the LLO (docker or k8s)
POST	/v1/service-components	Deploys a Service Component		CR in YAML
PUT	/v1/service-components	Replaces a deployed Service Component		CR in YAML
GET	/v1/service-components/{scName}	Retrieves a deployed Service Component	type: type of the LLO (docker or k8s)
PATCH	/v1/service-components/{scName}	updates a deployed Service Component	type: type of the LLO (docker or k8s)	CR in YAML
DELETE	/v1/service-components/{scName}	Deletes a deployed Service Component	type: type of the LLO (docker or k8s)