Experiences and Optimizations

Articles » Brownfield Network Automation with Ansible » Experiences and Optimizations

This article describes a solution Josef Fuchs, Network and Security Engineer at Pankl Racing Systems AG Austria developed while attending the Building Network Automation Solutions online course.

The Jinja2-only solution was working fine but suffers from poor performance when used on edge switches that have numerous managed client ports (some of my switches have up to 240 ports). The performance of looping over every single regex, parsing the whole configuration and rereading the result was not acceptable, so I optimized the configuration management by implementing two Jinja2 filters in Python. These filters work much faster than Ansible loops I used in the original solution.

Filter: ios_config_section_extract

This filter is used to extract a configuration section and optionally save it into a file. Here's how you could use it:

- set_fact:
    src_config: >
      {{ src_config | ios_config_section_extract(regexp,
                         ignorecase, prefix_str, filename) }}


The input (src_config) can be either a single string with line separators or a list of strings.


Parameter Required Default Description
regexp Yes A list of strings or a single string containing the regular expressions to select the configuration sections. Line start marker '^' or line end marker '$' are set by the filter when they're omitted. This ensures that the filter will (for example) match only interface configuration even when you pass plain interface name as the parameter.
ignorecase No false If set to true, the regex is case-insensitive.
prefix_str No '' Allows to prepend a common string to the all regular expression. This string will be directly prepended to every regular expression before the missing line-start and -end markers are added. For example, you can extract VLAN configurations if you pass the list of VLAN numbers as regexp parameter and 'vlan' as prefix_str.
filename No '' If a filename is specified, the selected configurations will be saved as a textfile. The directory must exist.


  • Selected configuration: list of strings
  • Textfile: if the filename parameter was specified, the textfile will contain the selected configuration sections

Filter: ios_config_section_remove

This filter deletes parts of device configuration. Here's the simplest way to use it:

- name: Remove all blocks or commands defined in delete_section_regex
    src_config: >
      {{ src_config |
           ios_config_section_remove(delete_section_regex) }}

This filter has the same input and parameters as the ios_config_section_extract filter and returns the contents of input configuration after deleting all configuration sections matched by regular expressions.

The full source code of the solution described in this article is available on GitHub. You can reach Josef through LinkedIn or email him at josef.fuchs (-at-)