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Extending onos-config with Model Plugins

onos-config is an extensible configuration management system, that allows the configuration of many different types and versions of devices to be managed concurrently.

Information models in YANG format (RFC 6020) can be used to accurately define the configuration and state objects and attributes of a device. In practice a device's object model usually comprises of a number of YANG files including augments and deviations, and must be considered as a combined unit.

In onos-config a set of these combined YANG files defining a particular version of a device type is known as a model.

Over its lifecycle onos-config will have to deal with many different models as its scope is expanded and as devices go through new release cycles. To allow this, models are loadable dynamically as plugins in the form of Linux or Mac shared object libraries (\*.so) using the YGOT library and are known as Model Plugins.

For convenience this shared object library is bundled up in to a docker image, and when loaded as a "sidecar" container in the onos-config Pod in Kubernetes will be copied across in to the pod (through a shared mounted folder), and loaded in to the main process.

The model plugin must have been built with the same version of "go" and with the same version of dependencies to load correctly.

The diagram shows the connection between the Model Plugin and the configuration store - linked by Device Type and Version. Effectively the primary key of the Model Registry is the Model Name and Version, whereas the primary key of the Configuration is the Device Name and Version.

onos-config internals

Role of the Model Plugin

The Model Plugin enables the following functionality in onos-config:

  1. Ensures that illegal values are not saved in to the configuration (this covers wrong data type, data values beyond range or not matching a pattern, lists that are not within their cardinality limits)
  2. Ensuring that read only values are not allowed to be set (changed).
  3. Checking the validity of stores on startup
  4. Enabling the Operational State cache within onos-config
  5. Enabling the retrieval of attributes by type - CONFIG or OPERATIONAL
  6. Enabling clients to access the model metadata through the Admin NBI
  7. Enabling JSON Payloads in gNMI SetRequests to be interpreted

Structure of a Model Plugin

A Model Plugin is mainly generated by the generator command from the YGOT project, and a wrapper modelmain.go implementing the ModelPlugin interface. They are compiled together with the go build command using the -buildmode=plugin option.

Many examples of Model Plugins are in the config-models repo, and an example script is available for creating new plugins.

ModelPlugin Interface

The model plugin must implement the ModelPlugin interface. This will allow it to be entered in to the Model Registry.

type ModelPlugin interface {
    ModelData() (string, string, []*gnmi.ModelData, string)
    UnmarshalConfigValues(jsonTree []byte) (*ygot.ValidatedGoStruct, error)
    Validate(*ygot.ValidatedGoStruct, ...ygot.ValidationOption) error
    Schema() (map[string]*yang.Entry, error)

Create your own Model Plugin using script

  1. Checkout the repo config-models
  2. Change directory in to config-models/modelplugins
  3. Copy anyone of the .env files to a new file
  4. Edit the variables at the top of the file to suit your plugin (see modelmain.go Definitions below for specifics), taking special care that the entries in MODELDATA are in alphabetical order (YANGDATA is derived from the MODELDATA but can be overridden if required)
  5. Make sure the required Yang files are present in the ./yang folder and named properly
  6. Run the script like
> ./ <filename>.env

Once the files are created:

  1. Change directory back to config-models
  2. Edit the Makefile to add a build and a docker target for your model plugin
  3. Edit the file config-models/cmd/dummy/dummy.go and add a dependency to your model plugin
  4. Compile the plugin with (replacing the name 'testdevice' and 'version' as appropriate)
make build/_output/
  1. Make the docker image (replacing the name 'testdevice' and 'version' as appropriate)
make config-plugin-docker-testdevice-1.0.0

Follow the steps in Loading the Model Plugin below for how to load it.

YANG files

The YANG files to be used with generator.go should be collected together in a folder and named in the style: \<modulename>@<latestrevision>.yang

Note The Yang files provided are required not to contain overlapping or clashing namespaces at the same path level. This requirement is necessary during the model compilation in YGOT because this tool offers no support for namespaces in the form of /namespace:path/path2, e.g. /openconfig-system:system/clock. YGOT compilation of a model containing /openconfig-system:system/clock will result in the path being /system/clock

Running the generator command in the form:

> go run $GOPATH/src/ \
-path yang -output_file=$TYPEVERSION/$TYPEVERSIONPKG/generated.go -package_name=$TYPEVERSIONPKG \
-generate_fakeroot $YANGLIST

will check all nested dependencies are present, and that the output is generated as a single file: generated.go.

Where $YANGLIST is a space separated list of YANG file names. See for an example

To visualize and further validate the collection of YANG files, the pyang tool can be used like:

> pyang -f tree $YANGLIST

Once the generator has run there is no need to persist the YANG files - the generated.go file contains all the information in an object model.

modelmain.go definitions

Examples of these definitions are given in the *.env files in the modelplugins folder.


This should be a name that defines the type of device, but should not include version. This name will be used later in the Configuration of the device. It should be between 4 and 40 chars and only include alphanumeric characters, dash, underscore and colon.


This should be the version number of the device in Semantic Versioning form. Only numeric characters and '.' character are allowed.


The primary YANG files of the device should be listed in the ModelData section of the modelmain.go file. These are the YANG files that define the top level containers and lists, and files that contain augments and deviations on these. During compilation other YANG files may get pulled in because they define reusable types (but should not be listed in model data).

Each entry in modeldata should be in the format of:


where: * name - the name of the module inside the YANG file and also the start of the name of the YANG file before @ * organization - the value from the organization field of the YANG file * version - in the name of the YANG file, which should correspond to the latest revision inside the YANG file - usually in the format of YYYY-MM-DD * altversion - an optional alternate version that will be listed as the version in the model plugin.

There should be no duplicate entries (of name) in the list and the list should be ordered alphabetically. Also there should be no ';' delimiter on the last item. See examples.

The modelmain.go file will have a MODELDATA section which is JSON formed from these variables.

Loading the Model Plugin

The Model Plugin can be loaded at the start up of onos-config by adding it to the plugins: section of the values.yaml file of the onos-config Helm Chart

This ensures that the model plugin is:

  1. loaded as a "sidecar" container in the onos-config K8s pod AND
  2. that the model plugin is given as a -modelPlugin argument to the onos-config command

See the Troubleshooting section below if onos-config fails to start because of a model plugin.

By default 4 plugins are loaded at startup:

-modelPlugin=/usr/local/lib/shared/ \
-modelPlugin=/usr/local/lib/shared/ \
-modelPlugin=/usr/local/lib/shared/ \

To see a list of loaded plugins use the onos-cli command:

> onos config get plugins

which gives an output like:

> onos config get plugins
TestDevice: 1.0.0 from containing:
    test1   2018-02-20  Open Networking Foundation

TestDevice: 2.0.0 from containing:
    test1   2019-06-10  Open Networking Foundation

Devicesim: 1.0.0 from containing:
    openconfig-interfaces   2017-07-14  OpenConfig working group
    openconfig-openflow 2017-06-01  OpenConfig working group
    openconfig-platform 2016-12-22  OpenConfig working group
    openconfig-system   2017-07-06  OpenConfig working group

Stratum: 1.0.0 from containing:
        openconfig-interfaces                 2.4.1    OpenConfig working group
        openconfig-if-ip                      3.0.0    OpenConfig working group
        openconfig-lacp                       1.1.1    OpenConfig working group
        openconfig-platform                   0.12.2   OpenConfig working group
        openconfig-platform-linecard          0.1.1    OpenConfig working group
        openconfig-platform-port              0.3.2    OpenConfig working group
        openconfig-platform-transceiver       0.7.0    OpenConfig working group
        openconfig-vlan                       3.2.0    OpenConfig working group
        openconfig-system                     0.7.0    OpenConfig working group
        openconfig-hercules-platform-linecard 0.2.0    OpenConfig working group
        openconfig-hercules-qos               0.1.0    OpenConfig working group
        openconfig-hercules-platform          0.2.0    OpenConfig working group
        openconfig-hercules-platform-chassis  0.2.0    OpenConfig working group
        openconfig-hercules-platform-port     0.2.0    OpenConfig working group
        openconfig-hercules                   0.2.0    OpenConfig working group
        openconfig-hercules-interfaces        0.2.0    OpenConfig working group
        openconfig-hercules-platform-node     0.2.0    OpenConfig working group

To see a list of Read-Only and Read-Write paths use the command with the verbose switch:

> onos config get plugins -v

In a distributed installation the ModelPlugin will have to be loaded on all running instances of onos-config.

Model Plugins and gNMI Capabilities

Capabilities on gNMI Northbound interface

The CapabilitiesResponse on the gNMI northound interface is generated dynamically from the modeldata section of all of the loaded Model Plugins.

Capabilities comparison on Southbound gNMI interface

At runtime when devices are connected to onos-config the response to the Capabilities request are compared with the modeldata for their corresponding ModelPlugin - if there is not an exact match a warning is displayed.

OpenConfig Models

Some devices that support OpenConfig Models report their capabilities using an OpenConfig versioning scheme e.g. 0.5.0, rather than the YANG revision date in the format 2017-07-06. If the device can correct its capabilities to give the revision then it should to be more consistent with non OpenConfig YANG models.

Accessing OpenConfig model of a specific revision requires a number of steps in Github.

For instance if a device reports it used openconfig-interfacess.yang 2.0.0, then to get this file do:

  • Browse to openconfig-interfaces.yang
  • Observe in the list of revision items in the YANG file that the reference 2.0.0 corresponds to a release date of 2017-07-14
  • Click in the History button
  • In the History page for this file, see that the next commit after this date was on Aug 9, 2017
  • Click on the related commit message
  • In the list of files modified in that commit click the ... next to the file openconfig-interfacess.yang and choose View File
  • In the page that displays the historical version of the file, click the Raw button
  • In the resulting raw display of the YANG file verify that the latest revision is 2017-07-14
  • Save the file locally as openconfig-interfaces@2017-07-14.yang

All the files in the yang folder were downloaded in this way. They are not strictly needed once generated.go has been created, but are kept here for convenience, saving to have to run the procedure above if a change was needed.

If the generator program reports that a dependency was required e.g. openconfig-inet-types.yang then the version of this file with a date equal to or before 2017-07-14 should be downloaded - it is openconfig-inet-types@2017-07-14.yang

Readonly paths in OpenConfig models

When an item in an Openconfig YANG file has "config false" it is effectively a read-only attribute. Usually with OpenConfig read-only objects are interspersed throughout the YANG model.

To see a list of Read Only paths use the command:

> onos config get plugins -v

When the Model Plugin is loaded, setting of an attribute like state/address should give an appropriate error

> gnmi_cli -address onos-config:5150 -set \
    -proto "update: <path: <target: 'devicesim-1', elem: <name: 'system'> elem: <name: 'openflow'> elem: <name: 'controllers'> elem: <name: 'controller' key: <key: 'name' value: 'main'>> elem: <name: 'connections'> elem: <name: 'connection' key: <key: 'aux-id' value: '0'>> elem: <name: 'state'> elem: <name: 'address'>> val: <string_val: ''>>" \
    -timeout 5s -en PROTO -alsologtostderr \
    -client_crt /etc/ssl/certs/client1.crt -client_key /etc/ssl/certs/client1.key -ca_crt /etc/ssl/certs/onfca.crt

gives the error:

rpc error: code = InvalidArgument desc = update contains a change to a read only
  path /system/openflow/controllers/controller[name=main]/connections/connection[aux-id=0]/state/address. Rejected


If the model plugin does not have exactly the same set of dependencies when compiled it will not be loaded correctly by onos-config at run time.

It might be seen as the onos-config pod entering an Error state e.g.

kubectl -n micro-onos get pods
NAME                           READY   STATUS    RESTARTS   AGE
onos-cli-68bbf4f674-fwkqc      1/1     Running   5          3d22h
onos-config-688b5697c8-zfq55   4/5     Error     0          64m
onos-config-raft-1-0           1/1     Running   0          64m
onos-topo-868cc6cf8c-bbrqh     1/1     Running   0          3h17m

This will give a fatal error such as plugin was built with a different version of package ..., which can be seen by getting the log from the failed container:

> kubectl -n micro-onos logs $(kubectl -n micro-onos get pods -l type=config -o name) onos-config

{"level":"info","ts":1583143084.8725095,"logger":"main","caller":"onos-config/onos-config.go:95","msg":"Starting onos-config"}
{"level":"info","ts":1583143084.9876108,"logger":"main","caller":"onos-config/onos-config.go:136","msg":"Topology service connected with endpoint onos-topo:5150"}
{"level":"info","ts":1583143084.9876873,"logger":"main","caller":"onos-config/onos-config.go:138","msg":"Network Configuration store connected"}
{"level":"info","ts":1583143085.004323,"logger":"main","caller":"onos-config/onos-config.go:149","msg":"Topology service connected with endpoint onos-topo:5150"}
{"level":"info","ts":1583143085.0043786,"logger":"manager","caller":"manager/manager.go:83","msg":"Creating Manager"}
{"level":"info","ts":1583143085.0044136,"logger":"main","caller":"onos-config/onos-config.go:154","msg":"Manager started"}
{"level":"info","ts":1583143085.004438,"logger":"modelregistry","caller":"modelregistry/modelregistry.go:161","msg":"Loading module /usr/local/lib/shared/"}
{"level":"info","ts":1583143085.0532916,"logger":"modelregistry","caller":"modelregistry/modelregistry.go:226","msg":"Model Devicesim 1.0.0 loaded. 37 read only paths. 113 read write paths"}
{"level":"info","ts":1583143085.0533392,"logger":"modelregistry","caller":"modelregistry/modelregistry.go:161","msg":"Loading module /usr/local/lib/shared/"}
{"level":"info","ts":1583143085.2057264,"logger":"modelregistry","caller":"modelregistry/modelregistry.go:218","msg":"Model Stratum 1.0.0 loaded. HARDCODED to 1 readonly path.1 read only paths. 9 read write paths"}
{"level":"info","ts":1583143085.205782,"logger":"modelregistry","caller":"modelregistry/modelregistry.go:161","msg":"Loading module /usr/local/lib/shared/"}
{"level":"warn","ts":1583143085.2160602,"logger":"modelregistry","caller":"modelregistry/modelregistry.go:164","msg":"Unable to load module /usr/local/lib/shared/ plugin.Open(\"/usr/local/lib/shared/\"): plugin was built with a different version of package"}
{"level":"fatal","ts":1583143085.2161112,"logger":"main","caller":"onos-config/onos-config.go:171","msg":"Unable to start onos-config plugin.Open(\"/usr/local/lib/shared/\"): plugin was built with a different version of package","stacktrace":"main.main\n\t/go/src/\nruntime.main\n\t/usr/local/go/src/runtime/proc.go:203"}

For the plugin to be loadable:

  1. the dependency must be listed in the go.mod at the root of config-models AND
  2. have the same version as listed in the go.mod at the root of onos-config

You should not add require entries to the go.mod of config-models directly, but instead add entries to the import section of cmd/dummy/dummy.go. When the make build target is run, go will add entries to go.mod based on the imports it finds in imports like this.

The versions or require entries in go.mod can be edited, to ensure that they match those of the go.mod at the root of onos-config.