A consul-template plugin to get EC2 metadata

README.md

ec2-consul-template-plugin

About

This is a simple little Python script to let you query EC2 metadata from consul-template. It's only requirement is boto. It uses the EC2 internal metadata service so it does not require any API keys or even a region. The only caveat is that this can only be run on a machine on EC2.

Usage

You can give no arguments for full dictionary output or one or more arguments to get specific key(s). Put it somewhere on your machine, chmod +x it and give the full path to consul-template.

Examples

Raw JSON (not very useful):

{{ plugin "ec2-consul-template-plugin.py" }}

Loop over the full JSON to get a specific key:

{{ with $d := plugin "ec2-consul-template-plugin.py" | parseJSON }}{{$d.placement.region}}{{end}}

Get a single key direct from the script:

{{ plugin "ec2-consul-template-plugin.py" "placement/region" }}

Get multiple keys direct from the script:

{{ with $d := plugin "ec2-consul-template-plugin.py" "local_ipv4" "hostname" | parseJSON }}{{$d.local_ipv4}} {{$d.hostname}}{{end}}

It supports xpath like queries. No array indexes or anything, just / (which seems to be in line with consul-template's existing functions).

For compatibility with consul-template, all dictionary keys have - replaced with _ i.e. local-ipv4 becomes local_ipv4. There are some deeply nested keys which aren't replaced (like in network).

ec2-consul-template-plugin.py

#!/usr/bin/env python
import sys
import json
import boto.utils

def xpath_get(mydict, path):
    elem = mydict
    try:
        for x in path.strip("/").split("/"):
            elem = elem.get(x)
    except:
        pass

    return elem

def mangle_keys(obj):
  for key in obj.keys():
    new_key = key.replace("-","_")
    if new_key != key:
      if isinstance(obj[key], dict):
        obj[new_key] = mangle_keys(obj[key])
      else:
        obj[new_key] = obj[key]
      del obj[key]
  return obj

metadata = boto.utils.get_instance_metadata()
metadata['user_data'] = boto.utils.get_instance_userdata()
metadata['identity'] = boto.utils.get_instance_identity()
metadata['placement']['region'] = metadata['identity']['document']['region']

metadata = mangle_keys(metadata)

if(len(sys.argv) > 1):
  if(len(sys.argv) > 2):
    output = {}
    for arg in sys.argv[1:]:
      output[arg] = xpath_get(metadata, arg)
    print json.dumps(output)
  else:
    if isinstance(xpath_get(metadata, sys.argv[1]), basestring):
      print xpath_get(metadata, sys.argv[1])
    else:
      print json.dumps(xpath_get(metadata, sys.argv[1]))
else:
  print json.dumps(metadata)