Ansible: Add elements to list
by yaobin.wen
Today, I needed to convert the following list config_original
config_original:
- iface: "enx00e07cc85b6e"
subnet: "192.168.16.0/24"
netmask: "255.255.255.0"
listen: "192.168.16.30"
range:
start: "192.168.16.1"
end: "192.168.16.28"
reserved:
- "192.168.16.29"
- iface: "enx241b7af8cdf1"
subnet: "192.168.16.0/24"
netmask: "255.255.255.0"
listen: "192.168.16.60"
range:
start: "192.168.16.31"
end: "192.168.16.58"
reserved:
- "192.168.16.59"
into the list config_modified as follows:
config_modified:
- iface: "enx00e07cc85b6e"
dhcp: off
subnet: "192.168.16.0/24"
netmask: "255.255.255.0"
static_ip_addresses:
- "192.168.16.29"
gateway: "192.168.16.1"
- iface: "enx241b7af8cdf1"
dhcp: off
subnet: "192.168.16.0/24"
netmask: "255.255.255.0"
static_ip_addresses:
- "192.168.16.59"
gateway: "192.168.16.31"
Basically, for every entry in config_original, I needed to:
- Remove the element
listenandrange. - Rename the field
reservedtostatic_ip_addresses. - Add the field
dhcpandgateway.
I examined the following filters:
json_querysubelements- Other JSON manipulation filters.
But none of them worked for me. JSONPath (as explained in JSONPath - XPath for JSON) looks promising initially but:
- Only the data is selected and the key is missing, so the result is not a
key-valuepair. For example, when I tried the JSONPath expression$..iface,subnet, I got:
[
"enx00e07cc85b6e",
"192.168.16.0/24",
"enx241b7af8cdf1",
"192.168.16.0/24"
]
- JSONPath doesn’t seem to support renaming the key name, so I couldn’t rename
reservedtostatic_ip_addresses.
Inspired by [1] and [2], I figured out the following playbook to do the conversion:
- name: Demo how to add elements to a list.
gather_facts: no
hosts: all
tasks:
- name: Define the original data.
set_fact:
config_original:
- iface: "enx00e07cc85b6e"
subnet: "192.168.16.0/24"
netmask: "255.255.255.0"
listen: "192.168.16.30"
range:
start: "192.168.16.1"
end: "192.168.16.28"
reserved:
- "192.168.16.29"
- iface: "enx241b7af8cdf1"
subnet: "192.168.16.0/24"
netmask: "255.255.255.0"
listen: "192.168.16.60"
range:
start: "192.168.16.31"
end: "192.168.16.58"
reserved:
- "192.168.16.59"
- name: Transform config_original to config_modified
vars:
config_modified: []
config_entry:
# `item` is re-evaluated in every iteration of the loop.
iface: "{ {item.iface} }"
dhcp: off
subnet: "{ {item.subnet} }"
netmask: "{ {item.netmask} }"
static_ip_address: "{ {item.reserved} }"
gateway: ~
set_fact:
config_modified: "{ {config_modified + [config_entry]} }"
loop: "{ {config_original} }"
- name: Display the final result.
debug:
var: config_modified
There are a few notes about the implementation:
- The variable
itemfromloopcan be used in a variable that’s defined invars.itemis re-evaluated in every iteration of the loop so the value of the variable changes accordingly. - The variable evaluation (
{ {var} }) is Jinja2 evaluation which is essentially Python code. Soconfig_modified + [config_entry]means “putconfig_entryinto a list and use this list to extend the currentconfig_modified”. This is the key thatconfig_modifiedgets extended instead of being overwritten.
The output of the debug task confirms the modification:
TASK [Display the final result.] ********************************
ok: [localhost] =>
config_modified:
- dhcp: false
gateway: null
iface: enx00e07cc85b6e
netmask: 255.255.255.0
static_ip_address:
- 192.168.16.29
subnet: 192.168.16.0/24
- dhcp: false
gateway: null
iface: enx241b7af8cdf1
netmask: 255.255.255.0
static_ip_address:
- 192.168.16.59
subnet: 192.168.16.0/24
References:
Tags: Tech