Junos PyEZ with Jinja2 templates

Table of Contents

1. Quick Jinja2 Demo using the Python Interpreter

2. Simple Python script with a Jinja2 Template

3. Python Script with Jinja2 using YAML files

1. Quick Jinja2 Demo using the Python Interpreter

2. Simple Python script with a Jinja2 Template

3. Python Script with Jinja2 using YAML files

1. Quick Jinja2 Demo using the Python Interpreter

This is just a short demo to quickly show how Jinja2 templates work with Python

---

1.1 Start a Docker container for the PyEZ environment

Using a Docker container greatly simplifies the environment setup for Python, PyEz and Ansible... It also keeps things clean and contained

docker pull juniper/pyez-ansible

docker run -it --rm -v $(pwd):/project juniper/pyez-ansible

<<<<<<< HEAD See Docker Hub for more info:

• https://hub.docker.com/r/juniper/pyez-ansible/

If you need access to some Junos devices for lab / testing purposes, you can run vSRX or vQFX vagrant images:

• vSRX image on Vagrant Cloud:
  • https://app.vagrantup.com/juniper/boxes/ffp-12.1X47-D15.4-packetmode
• vQFX image on Vagrant Cloud:
  • https://app.vagrantup.com/juniper/boxes/vqfx10k-re
• Examples of multi VMs topologies:
  • https://github.com/Juniper/vqfx10k-vagrant

======= See Docker Hub for more info https://hub.docker.com/r/juniper/pyez-ansible/

809b69b4d307698472ee5ce6e9918a42b4adaa32

1.2 Start the Python interpreter

python

1.3 Getting the jinja2 module

Import the "Template" method from the jinja2 module

from jinja2 import Template 

1.4 Instanciating Template()

Create an instance of Template with my interface address variables. Jinja2 identifies the variables by using double curly brackets.

For example, if I want to configure a number of interfaces on a Junos device with an IPv4 address, I can use the following syntax with 3 variables: the IFD (physical interface name), the unit and an IP address:

template = Template('set interface {{ ifd }} unit {{ unit }} family inet address {{ ip }}')

1.5 Using render()

The template object provides a method called render() which, when called with a dict or keyword arguments, expands the template

Now you can "expand" the variables with some values:

template.render(ifd='ge-0/0/0',unit='101',ip='10.0.1.1/24’)

And you can repeat that many times with different values:

template.render(ifd='ge-0/0/0',unit='102',ip='10.0.2.1/24’)

1.6 Stop the Python interpreter

Use Ctrl-D or:

exit()

2. Simple Python script with a Jinja2 Template

Now instead of using the Python interpreter I can write a script that does the same thing.

2.1 Writing a simple Python script

Write a script called "genconfig.py" that includes the same jinja2 template. We then expand the variables with render() method for two logical interfaces and print the results. <<<<<<< HEAD

#!/usr/bin/env python

from jinja2 import Template
template = Template('set interface {{ ifd }} unit {{ unit }} family inet address {{ ip }}')
ifa1 = template.render(ifd='ge-0/0/0',unit='101',ip='10.0.1.1/24')
print ifa1
ifa2 = template.render(ifd='ge-0/0/0',unit='102',ip='10.0.2.1/24')
print ifa2

2.2 Setting file permissions

Make sure the access permissions are properly set to execute this script

chmod +x genconfig.py

2.3 Running the Python script

Now you're ready to call that script:

./genconfig.py

or

python genconfig.py

Done.

3. Python Script with Jinja2 using YAML files

Writing variables within the script means you need to update the script for every variable change. Instead you can store the variables in a separate file written in YAML format which is easy to read/update and much cleaner. It's also a good idea to write your jinja2 template in a separate file while we're at it.

3.1 Jinja2 Template file

Write a jinja2 template called "conf.j2":

In 'set commands' format:

{% for item in ifd %}
set interfaces {{ item.name }} unit {{ item.unit }} family int address {{ item.ip }}
{% endfor %}

Or in 'curly bracket' style:

interfaces {
{% for item in ifd %}
    {{ item.name }} {
        unit {{ item.unit }} {
            family inet {
                address {{ item.ip }};
            }
        }
    }
{% endfor %}
}

3.2 YAML file for Variables

Store the variables in a YAML file called "ifvars.yml":

---
ifd:
- name: 'ge-0/0/1'
  unit: 0
  ip: 10.0.1.1/24
- name: ge-0/0/2 
  unit: 0
  ip: 10.0.2.1/24
- name: ge-0/0/3
  unit: 0
  ip: 10.0.3.1/24 
- name: ge-0/0/4
  unit: 0
  ip: 10.0.4.1/24
- name: ge-0/0/5
  unit: 0
  ip: 10.0.5.1/24

3.3 Writing a simple Python script

Write a script called "genconfig.py" that includes the same jinja2 template. We then expand the variables with render() method for two logical interfaces and print the results. <<<<<<< HEAD

#!/usr/bin/env python

import yaml
from jinja2 import Template

mytemplate = "setconf.j2"
myinput = "ifd.yml"

### Print the Jinja2 Template file
myj2 = open(mytemplate.read())
#print "\n### DEBUG: Print the Jinja2 template:"
#print myj2

### Print the YAML input file
mydata = yaml.load(open(myinput).read())
#print "\n### DEBUG: Print the YAML file:"
#print mydata

### Render the jinja2 template
mytemplate = Template(myj2)
myconfig = mytemplate.render(mydata)
print "\n### Here's the full config:"
print myconfig

3.4 Setting file permissions

Make sure the access permissions are properly set to execute this script

chmod +x genconfig.py

3.5 Running the Python script

Now you're ready to call that script:

./genconfig.py

or

python genconfig.py

Done.