Recommended file format (YAML? JSON? Other?) - json

Question

Before I start I should state that I'm new to both YAML and JSON so the rules of formatting are not that clear.
I'm trying to write a Perl script (Perl because I know it to exist on all of our servers.) which will update several network-related settings for various hosts. My preference is to have all of the settings in a single file and update the configurations based on which host the script is running on.
I looked at YAML, but I'm a bit put off by the fact that I can't do something like:
host:
hostname: first
interface: eth0
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
interface: eth1
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
host:
hostname: second
interface: eth0
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
interface: eth1
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
That is to say, I've plugged this into YAML validators and it has failed.
I have figured out that, for YAML, I can do the following:
host: "first"
interface1:
name: eth0
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
interface2:
name: eth1
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
This is less than desirable, though, as it makes having multiple hosts in one file impossible. I'm basing this on the fact that I keep getting errors from the online validators that I've used when I do attempt this.
I've looked at using JSON, but I don't know all of the rules for that either. I do know that the following does not work:
{
"host": "first",
"interface1": {
"newip": "2.3.4.5",
"oldip": "1.2.3.4",
"oldgw": "1.2.3.1",
"name": "eth0",
"newgw": "2.3.4.1"
},
"interface2": {
"newip": "2.3.4.5",
"oldip": "1.2.3.4",
"oldgw": "1.2.3.1",
"name": "eth1",
"newgw": "2.3.4.1"
}
}
{
"host": "second",
"interface1": {
"newip": "2.3.4.5",
"oldip": "1.2.3.4",
"oldgw": "1.2.3.1",
"name": "eth0",
"newgw": "2.3.4.1"
},
"interface2": {
"newip": "2.3.4.5",
"oldip": "1.2.3.4",
"oldgw": "1.2.3.1",
"name": "eth1",
"newgw": "2.3.4.1"
}
}
Is there a format I can use that will allow me to store all of the host and their information in a single file that can be parsed?
If either YAML or JSON are suitable, what am I doing wrong?

Answer 1

Your YAML problem with host is the same as what it was initially with interface: You're trying to put subkeys at the same level as the keys that contain them.
host:
name: first
interface1:
name: eth0
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
interface2:
name: eth1
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
should work, although that still doesn't address your need for multiple hosts. For that (and to better handle multiple interfaces), you should use lists:
host:
- name: first_host
interface:
- name: eth0
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
- name: eth1
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
- name: second_host
interface:
- ...
When read in by Perl, this will give you the structure:
{
"host": [
{
"interface": [
{
"newip": "2.3.4.5",
"oldip": "1.2.3.4",
"oldgw": "1.2.3.1",
"name": "eth0",
"newgw": "2.3.4.1"
},
{
"newip": "2.3.4.5",
"oldip": "1.2.3.4",
"oldgw": "1.2.3.1",
"name": "eth1",
"newgw": "2.3.4.1"
}
],
"name": "first_host"
}
]
}
As far as JSON, that's a subset of YAML. Personally, I prefer to have the full YAML spec available to me, but JSON provides more interoperability with non-Perl languages.

Answer 2

I'd prefer JSON over YAML. I recently built a system whose "user interface" (ha) was basically one giant config file; the user needed to edit that config file to control the system; and I used YAML for that file. It turns out that YAML has a few really annoying gotchas that make it unsuitable for humans -- it's very picky about whitespace, for example.
Also, it's less familiar in general: I'd guess that anyone with programming experience has run into JSON, and understands it. But YAML is more niche.
If you're not using the advanced features of YAML -- such as the ability to define variables and then reference them later -- I'd recommend that you go with JSON instead.

Answer 3

Do not care about the format. Populate a data structure and let JSON or YAML do the dirty work for you. If you are going to produce and parse the files yourself anyway, there is almost no advantage in using JSON or YAML.

Answer 4

The exact format is unimportant: both YAML and JSON are fine. Actually, I would recommend to keep this specific part pluggable.
The issue with your YAML is that the data structure has to make some sense, e.g.:
- host:
hostname: first
interfaces:
eth0:
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
eth1:
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
- host:
hostname: second
interfaces:
...
Or if the interfaces have to be ordered:
- host:
hostname: first
interfaces:
-
name: eth0
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
-
name: eth1
oldip: 1.2.3.4
newip: 2.3.4.5
oldgw: 1.2.3.1
newgw: 2.3.4.1
If writing YAML manually is to tedious for you, just write a small script that generates it for you.
Note that lists have to be somehow introduces by a marker like -. Intendation is not sufficient for this.