Example Service Tutorial

This tutorial uses ExampleService to illustrate how to write and on-board a service in CORD. ExampleService is a multi-tenant service that instantiates a VM instance on behalf of each tenant, and runs an Apache web server in that VM. This web server is then configured to serve a tenant-specified message (a string), where the tenant is able to set this message using CORD's control interface. From a service modeling perspective, ExampleService extends the base Service model with two fields:

• service_message: A string that contains a message to display for the service as a whole (i.e., to all tenants of the service).
• tenant_message: A string that is displayed for a specific Tenant.

These two fields are a simple illustration of a common pattern. A service model typically includes fields used to configure the service as a whole (service_message in this example) and fields used to control individual instances of the the service (tenant_message in this example). It would be common for the operator to set configuration-related fields when the service first starts up, and then set/adjust control-related fields on behalf of individual tenants as the service runs.

Tenant and ServiceInstance are two closely related terms. "Tenant" refers to the user or the consumer of a service. Often we partition a service into several pieces, each for use by a tenant, thus making it a multi-tenant service. Each one of these tenant-specific pieces is referred to as a ServiceInstance.

Summary

The result of preparing ExampleService for on-boarding is the following set of files, all located in the xos directory of the exampleservice repository. (There are other helper files, as described throughout this tutorial.)

Earlier releases (3.0 and before) required additional files (mostly Python code) to on-board a service, including a REST API, a TOSCA API, and an Admin GUI. These components are now auto-generated from the models rather than coded by hand, although it is still possible to extend the GUI.

Development Environment

For this tutorial we recommend using a Virtual Pod (CiaB) as your development environment. By default CiaB brings up OpenStack, ONOS, and XOS running the R-CORD collection of services. This tutorial demonstrates how to add a new customer-facing service to R-CORD.

A Virtual Pod includes a build machine, a head node, switches, and a compute node all running as VMs on a single host. Before proceeding you should familiarize yourself with the CiaB environment and the POD Development Loop.

Define a Model

The first step is to create a set of models for the service. To do this, create a file named exampleservice.xproto in your service's xos directory. This file encodes the models in the service in a format called xproto which is a combination of Google Protocol Buffers and some XOS-specific annotations to facilitate the generation of service components, such as the GRPC and REST APIs, security policies, and database models among other things. It consists of two parts:

• The Service model, which manages the service as a whole.

• The ServiceInstance model, which manages tenant-specific (per-service-instance) state.

Service Model (per-Service state)

A Service model extends (inherits from) the XOS base Service model. At its head is a set of option declarations: the name of the service as a configuration string, and as a human readable one. Then follows a set of field definitions.

message ExampleService (Service){
    option name = "exampleservice";
    option verbose_name = "Example Service";
    required string service_message = 1 [help_text = "Service Message to Display", max_length = 254, null = False, db_index = False, blank = False];
}

ServiceInstance Model (per-Tenant state)

Your ServiceInstance model will extend the core TenantWithContainer class, which is a Tenant that creates a VM instance:

message ExampleServiceInstance (TenantWithContainer){
     option name = "exampleserviceinstance";
     option verbose_name = "Example Service Instance";
     required string tenant_message = 1 [help_text = "Tenant Message to Display", max_length = 254, null = False, db_index = False, blank = False];
}

The following field specifies the message that will be displayed on a per-Tenant basis:

tenant_message = models.CharField(max_length=254, help_text="Tenant Message to Display")

Think of this as a tenant-specific (per service instance) parameter.

Define a Synchronizer

The second step is to define a synchronizer for the service. Synchronizers are processes that run continuously, checking for changes to service's model(s). When a synchronizer detects a change, it applies that change to the underlying system. For ExampleService, the ServiceInstance model is the model we will want to synchronize, and the underlying system is a compute instance. In this case, we’re using TenantWithContainer to create this instance for us.

XOS Synchronizers are typically located in the xos/synchronizer directory of your service.

Note: Earlier versions included a tool to track model dependencies, but today it is sufficient to create a file named model-deps with the contents:{}.

The Synchronizer has two parts: A container that runs the synchronizer process, and an Ansible playbook that configures the underlying system. The following describes how to construct both.

Synchronizer Container

First, create a file named exampleservice-synchronizer.py:

#!/usr/bin/env python
# Runs the standard XOS synchronizer

import importlib
import os
import sys
from xosconfig import Config

config_file = os.path.abspath(os.path.dirname(os.path.realpath(__file__)) + '/exampleservice_config.yaml')
Config.init(config_file, 'synchronizer-config-schema.yaml')

synchronizer_path = os.path.join(os.path.dirname(
    os.path.realpath(__file__)), "../../synchronizers/new_base")
sys.path.append(synchronizer_path)
mod = importlib.import_module("xos-synchronizer")
mod.main()

The above is boilerplate. It loads and runs the default xos-synchronizer module in it’s own Docker container. To configure this module, create a file named exampleservice_config.yaml, which specifies various configuration and logging options:

name: exampleservice-synchronizer
accessor:
  username: xosadmin@opencord.org
  password: "@/opt/xos/services/exampleservice/credentials/xosadmin@opencord.org"
required_models:
  - ExampleService
  - ExampleServiceInstance
  - ServiceDependency
  - ServiceMonitoringAgentInfo
dependency_graph: "/opt/xos/synchronizers/exampleservice/model-deps"
steps_dir: "/opt/xos/synchronizers/exampleservice/steps"
sys_dir: "/opt/xos/synchronizers/exampleservice/sys"
model_policies_dir: "/opt/xos/synchronizers/exampleservice/model_policies"

NOTE: Historically, synchronizers were named “observers”, so s/observer/synchronizer/ when you come upon this term in the XOS code and documentation.

Second, create a directory within your synchronizer directory named steps. In steps, create a file named sync_exampleserviceinstance.py:

import os
import sys
from synchronizers.new_base.SyncInstanceUsingAnsible import SyncInstanceUsingAnsible
from synchronizers.new_base.modelaccessor import *
from xos.logger import Logger, logging

parentdir = os.path.join(os.path.dirname(__file__), "..")
sys.path.insert(0, parentdir)

logger = Logger(level=logging.INFO)

Bring in some basic prerequities. Also include the models created earlier, and SyncInstanceUsingAnsible which will run the Ansible playbook in the Instance VM.

class SyncExampleServiceInstance(SyncInstanceUsingAnsible):

    provides = [ExampleServiceInstance]

    observes = ExampleServiceInstance

    requested_interval = 0

    template_name = "exampleserviceinstance_playbook.yaml"

    service_key_name = "/opt/xos/synchronizers/exampleservice/exampleservice_private_key"

    def __init__(self, *args, **kwargs):
        super(SyncExampleServiceInstance, self).__init__(*args, **kwargs)

    def get_exampleservice(self, o):
        if not o.owner:
            return None

        exampleservice = ExampleService.objects.filter(id=o.owner.id)

        if not exampleservice:
            return None

        return exampleservice[0]

    # Gets the attributes that are used by the Ansible template but are not
    # part of the set of default attributes.
    def get_extra_attributes(self, o):
        fields = {}
        fields['tenant_message'] = o.tenant_message
        exampleservice = self.get_exampleservice(o)
        fields['service_message'] = exampleservice.service_message
        return fields

    def delete_record(self, port):
        # Nothing needs to be done to delete an exampleservice; it goes away
        # when the instance holding the exampleservice is deleted.
        pass

Third, create a run-from-api.sh file for your synchronizer.

python exampleservice-synchronizer.py

Finally, create a Dockerfile for your synchronizer, name it Dockerfile.synchronizer and place it in the synchronizer directory with the other synchronizer files:

FROM xosproject/xos-synchronizer-base:candidate

COPY . /opt/xos/synchronizers/exampleservice

ENTRYPOINT []

WORKDIR "/opt/xos/synchronizers/exampleservice"

# Label image
ARG org_label_schema_schema_version=1.0
ARG org_label_schema_name=exampleservice-synchronizer
ARG org_label_schema_version=unknown
ARG org_label_schema_vcs_url=unknown
ARG org_label_schema_vcs_ref=unknown
ARG org_label_schema_build_date=unknown
ARG org_opencord_vcs_commit_date=unknown
ARG org_opencord_component_chameleon_version=unknown
ARG org_opencord_component_chameleon_vcs_url=unknown
ARG org_opencord_component_chameleon_vcs_ref=unknown
ARG org_opencord_component_xos_version=unknown
ARG org_opencord_component_xos_vcs_url=unknown
ARG org_opencord_component_xos_vcs_ref=unknown

LABEL org.label-schema.schema-version=$org_label_schema_schema_version \
      org.label-schema.name=$org_label_schema_name \
      org.label-schema.version=$org_label_schema_version \
      org.label-schema.vcs-url=$org_label_schema_vcs_url \
      org.label-schema.vcs-ref=$org_label_schema_vcs_ref \
      org.label-schema.build-date=$org_label_schema_build_date \
      org.opencord.vcs-commit-date=$org_opencord_vcs_commit_date \
      org.opencord.component.chameleon.version=$org_opencord_component_chameleon_version \
      org.opencord.component.chameleon.vcs-url=$org_opencord_component_chameleon_vcs_url \
      org.opencord.component.chameleon.vcs-ref=$org_opencord_component_chameleon_vcs_ref \
      org.opencord.component.xos.version=$org_opencord_component_xos_version \
      org.opencord.component.xos.vcs-url=$org_opencord_component_xos_vcs_url \
      org.opencord.component.xos.vcs-ref=$org_opencord_component_xos_vcs_ref

CMD bash -c "cd /opt/xos/synchronizers/exampleservice; ./run-from-api.sh"

Synchronizer Playbooks

In the same steps directory, create an Ansible playbook named exampleserviceinstance_playbook.yml which is the “master playbook” for this set of plays:

# exampletenant_playbook

- hosts: "{{ instance_name }}"
  connection: ssh
  user: ubuntu
  sudo: yes
  gather_facts: no
  vars:
    - tenant_message: "{{ tenant_message }}"
    - service_message: "{{ service_message }}"

This sets some basic configuration, specifies the host this Instance will run on, and the two variables that we’re passing to the playbook.

roles:
  - install_apache
  - create_index

This example uses Ansible’s Playbook Roles to organize steps, provide default variables, organize files and templates, and allow for code reuse. Roles are created by using a set directory structure.

In this case, there are two roles, one that installs Apache, and one that creates the index.html file from a Jinja2 template.

Create a directory named roles inside steps, then create two directories named for your roles: install_apache and create_index.

Within install_apache, create a directory named tasks, then within that directory, a file named main.yml. This will contain the set of plays for the install_apache role. To that file add the following:

- name: Install apache using apt
  apt:
    name=apache2
    update_cache=yes

This will use the Ansible apt module to install Apache.

Next, within create_index, create two directories, tasks and templates. In templates, create a file named index.html.j2, with the contents:

ExampleService
 Service Message: "{{ service_message }}"
 Tenant Message: "{{ tenant_message }}"

These Jinja2 Expressions will be replaced with the values of the variables set in the master playbook.

In the tasks directory, create a file named main.yml, with the contents:

- name: Write index.html file to apache document root
  template:
    src=index.html.j2
    dest=/var/www/html/index.html

This uses the Ansible template module to load and process the Jinja2 template then put it in the dest location. Note that there is no path given for the src parameter: Ansible knows to look in the templates directory for templates used within a role.

As a final step, you can check your playbooks for best practices with ansible-lint if you have it available.

Define an On-boarding Spec

The final step is to define an on-boarding recipe for the service. By convention, we use <servicename>-onboard.yaml, and place it in the xos directory of the service.

The on-boarding recipe is a TOSCA specification that lists all of the resources for your synchronizer. It's basically a collection of everything that has been created above. For example, here is the on-boarding recipe for ExampleService:

tosca_definitions_version: tosca_simple_yaml_1_0

description: Onboard the exampleservice

imports:
   - custom_types/xos.yaml

topology_template:
  node_templates:
    exampleservice:
      type: tosca.nodes.ServiceController
      properties:
          base_url: file:///opt/xos_services/exampleservice/xos/
          # The following will concatenate with base_url automatically, if
          # base_url is non-null.
          xproto: ./
          tosca_custom_types: exampleservice.yaml
          tosca_resource: tosca/resources/exampleservice.py, tosca/resources/exampleserviceinstance.py
          private_key: file:///opt/xos/key_import/exampleservice_rsa
          public_key: file:///opt/xos/key_import/exampleservice_rsa.pub

You will also need to modify the profile-manifest in platform-install to on-board your service. To do this, modify the xos_services and xos_service_sshkeys sections as shown below:

xos_services:
  ... (lines omitted)
  - name: exampleservice
    path: orchestration/xos_services/exampleservice
    keypair: exampleservice_rsa
    synchronizer: true

xos_service_sshkeys:
  ... (lines omitted)
  - name: exampleservice_rsa
    source_path: "~/.ssh/id_rsa"

The above modifications to the profile manifest will cause the build procedure to automatically install an ssh key for your service, and to onboard the service at build time.