Template network config generation with Python and Jinja2

What is this?

A Python script that generates a Cisco config *. A sample that fills parameters using Jinja2. It seems to be very versatile, so make a note for yourself. If you prepare two config templates including variables and CSV that summarizes the values for variables and execute the script, multiple configs will be output as files.

• Of course you don't have to be Cisco.

What is Jinja2?

Template engine for Python. For more information, see Honke.

Origin of Jinja2 Naming

The name Jinja was chosen because it’s the name of a Japanese temple and temple and template share a similar pronunciation. It is not named after the city in Uganda.

Japanese temples (shrines) have similar pronunciations to templates. (There is a city called Jinja in Uganda, but that's not it)

0. Preparation

Make Jinja2 available with pip. Prepare three files and one directory (each explained below).

~ $pip3 list | grep Jinja2
Jinja2 (2.8)
~ $ls
build_templates.py	config_template.txt	configs			inventory.csv
~ $

1. configs ... Directory where multiple config files are generated. The contents are empty.
2. inventory.csv ... config template variable file.
3. config_template.txt ... config template file.
4. build_templates.py ... main script.

1. configs directory

It's empty.

~ $ls ./configs
~ $

2. inventory.csv You can create it in Excel, or you can manage variables with a script.

~ $cat inventory.csv 
hostName,serialNumber,platformId,site,ipAddress,subnet,username,password,enablepass
Cat01,12345678901,WS-C2960X-48FPD-L,Tokyo,10.10.10.101,255.255.255.0,cisco,C1sco12345,C1$co
Cat02,22345678901,WS-C2960X-48FPD-L,Osaka,10.10.10.102,255.255.255.0,cisco,C1sco12345,C1$co
Cat03,32345678901,WS-C2960X-48FPD-L,Nagoya,10.10.10.103,255.255.255.0,cisco,C1sco12345,C1$co

3. config_template.txt The config is familiar to network engineers, but the parameter you want to complement dynamically is {{variable}}. Since Jinja2 is also used in Ansible, there may be many people who do not feel uncomfortable.

~ $cat config_template.txt 
hostname {{hostName}}
!
enable password {{enablepass}}
!
username {{username}} password 0 {{password}}
no aaa new-model
!
int vlan 1
ip address {{ipAddress}} {{subnet}}
!
end

• Reference: Templating of Ansible Docs

As already referenced in the variables section, Ansible uses Jinja2 templating to enable dynamic expressions and access to variables.

4. build_templates.py build_templates is a sample function that inputs a config template (config_template.txt) and a variable CSV (inventory.csv) and outputs multiple config files.

build_templates.py

# -*- coding: utf-8 -*-
import jinja2
import csv

CONFIGS_DIR= "./configs/"
DEVICES="./inventory.csv"
TEMPLATE="./config_template.txt"

def build_templates(template_file, devices):

    templateLoader = jinja2.FileSystemLoader('./')
    templateEnv = jinja2.Environment(loader=templateLoader)
    template = templateEnv.get_template(template_file)

    f = open(devices, 'rt')
    try:
        reader = csv.DictReader(f)
        for dict_row in reader:
            outputText = template.render(dict_row)

            config_filename = CONFIGS_DIR + dict_row['hostName'] + '-' + dict_row['site'] + '-config'
            with open(config_filename, 'w') as config_file:
                config_file.write(outputText)
            print("Config generation: %s" % config_filename)

    finally:
        f.close()

if __name__ == "__main__":
    build_templates(TEMPLATE, DEVICES)

point

--Read line by line (device by device) from CSV file with Python dictionary (csv.DictReader) --Variable completion (template.render (dict_row)) to template and output --Loop as many as the number of devices (for dict_row in reader) ――The way to write Jinja2 is written separately, but it seems that you can write even one as follows.

• Source: Load a Jinja2 template from the filesystem and render it

Quote

import os
import jinja2


def render(tpl_path, context):
    path, filename = os.path.split(tpl_path)
    return jinja2.Environment(
        loader=jinja2.FileSystemLoader(path or './')
    ).get_template(filename).render(context)

5. Run

~ $python3 build_templates.py 
Config generation: ./configs/Cat01-Tokyo-config
Config generation: ./configs/Cat02-Osaka-config
Config generation: ./configs/Cat03-Nagoya-config
~ $
~ $ls ./configs/
Cat01-Tokyo-config	Cat02-Osaka-config	Cat03-Nagoya-config
~ $
~ $cat ./configs/Cat01-Tokyo-config 
hostname Cat01
!
enable password C1$co
!
username cisco password 0 C1sco12345
no aaa new-model
!
int vlan 1
ip address 10.10.10.101 255.255.255.0
!
end
~ $
~ $
~ $cat ./configs/Cat02-Osaka-config 
hostname Cat02
!
enable password C1$co
!
username cisco password 0 C1sco12345
no aaa new-model
!
int vlan 1
ip address 10.10.10.102 255.255.255.0
!
end
~ $
~ $

it is a good feeling. It seems that it can be used for other purposes.

reference

Usage of csv.DictReader ... Easy-to-understand explanation of CSV parsing CiscoDevNet / apic-em-samples-aradford ... It's messy, but it contains a lot.