Navigating CORD

Understanding the relationship between installing, operating, and developing CORD—and the corresponding toolsets and specification files used by each stage—is helpful in navigating CORD.

• Installation (Helm): Installing CORD means installing a collection of Docker containers in a Kubernetes cluster. We use Helm to carry out the installation, with the valid configurations defined by a set of helm-charts. These charts specify the version of each container to be deployed, and so they also play a role in upgrading a running system. More information about helm-charts can be found here.

• Operations (TOSCA): A running CORD POD supports multiple Northbound Interfaces (e.g., a GUI and REST API), but we typically use TOSCA to specify a workflow for configuring and provisioning a running system. A freshly installed CORD POD has a set of control plane and platform level containers running (e.g., XOS, ONOS, OpenStack), but until provisioned using TOSCA, there are no services and no service graph. More information about TOSCA can be found here.

• Development (XOS): The services running in an operational system are typically deployed as Docker containers, paired with a model that specifies how the service is to be on-boarded into CORD. This model is writen in the xproto modeling language, and processed by the XOS tool-chain. Among other things, this tool-chain generates the TOSCA-engine that is used to process the configuration and provisioning workflows used to operate CORD. More information about xproto (and other details about on-boarding a service) can be found here.

These tools and containers are inter-related as follows:

• An initial install brings up a set of XOS-related containers (e.g., xos-core, xos-gui, xos-tosca) that have been configured with a base set of models. Of these, the xos-tosca container implements the TOSCA engine, which takes TOSCA workflows as input and configures/provisions CORD accordingly.

• While the install and operate stages are distinct, for convenience, some helm-charts elect to launch a tosca-loader container (in Kubernetes parlance, it's a job and not a service) to load an initial TOSCA workflow into a newly deployed set of services. This is how a service graph is typically instantiated.

• While the CORD control plane is deployed as a set of Docker containers, not all of the services themselves run in containers. Some services run in VMs managed by OpenStack (this is currently the case for M-CORD) and some services are implemented as ONOS applications that have been packaged using Maven. In such cases, the VM image and the Maven package are still specified in the TOSCA workflow.

• Every service (whether implemented in Docker, OpenStack, or ONOS) has a counter-part synchronizer container running as part of the CORD control plane (e.g., volt-synchronizer for the vOLT service). Typically, the helm-chart for a service launches this synchronizer container, whereas the TOSCA worflow creates, provisions, and initializes the backend container, VM, or ONOS app.

• Bringing up additional services in a running POD involves executing helm-charts to install the new service's synchronizer container, which in turn loads the corresponding new models into XOS. This load then triggers and upgrade and restart of the TOSCA engine (and other NBIs), which is a pre-requisite for configuring and provisioning that new service.

• Upgrading an existing service is similar to bringing up a new service, where we depend on Kubernetes to incrermentally roll out the containers that implement the service (and rollback if necessarily), and we depend on XOS to migrate from the old model to the new model (and support both old and new APIs during the transition period). Upgrading existing services has not been thoroughly tested.