Module: Ohai::Mixin::Ec2Metadata

Defined in:
lib/ohai/mixin/ec2_metadata.rb

Overview

This code parses the EC2 Instance Metadata API to provide details of the running instance.

Earlier version of this code assumed a specific version of the metadata API was available. Unfortunately the API versions supported by a particular instance are determined at instance launch and are not extended over the life of the instance. As such the earlier code would fail depending on the age of the instance.

The updated code probes the instance metadata endpoint for available versions, determines the most advanced version known to work and executes the metadata retrieval using that version.

If no compatible version is found, an empty hash is returned.

Instance Method Summary collapse

Instance Method Details

#best_api_version ⇒ Object 



50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
 
# File 'lib/ohai/mixin/ec2_metadata.rb', line 50

def best_api_version
  @api_version ||= begin
    logger.trace("Mixin EC2: Fetching http://#{EC2_METADATA_ADDR}/ to determine the latest supported metadata release")
    response = http_client.get("/")
    if response.code == "404"
      logger.trace("Mixin EC2: Received HTTP 404 from metadata server while determining API version, assuming 'latest'")
      return "latest"
    elsif response.code != "200"
      raise "Mixin EC2: Unable to determine EC2 metadata version (returned #{response.code} response)"
    end
    # Note: Sorting the list of versions may have unintended consequences in
    # non-EC2 environments. It appears to be safe in EC2 as of 2013-04-12.
    versions = response.body.split("\n").sort
    until versions.empty? || EC2_SUPPORTED_VERSIONS.include?(versions.last)
      pv = versions.pop
      logger.trace("Mixin EC2: EC2 lists metadata version: #{pv} not yet supported by Ohai") unless pv == "latest"
    end
    logger.trace("Mixin EC2: Latest supported EC2 metadata version: #{versions.last}")
    if versions.empty?
      raise "Mixin EC2: Unable to determine EC2 metadata version (no supported entries found)"
    end

    versions.last
  end
end

#fetch_dir_metadata(id, api_version) ⇒ Object 



137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
 
# File 'lib/ohai/mixin/ec2_metadata.rb', line 137

def fetch_dir_metadata(id, api_version)
  metadata = {}
  retrieved_metadata = metadata_get(id, api_version)
  if retrieved_metadata
    retrieved_metadata.split("\n").each do |o|
      key = expand_path(o)
      if key[-1..-1] != "/"
        retr_meta = metadata_get("#{id}#{key}", api_version)
        metadata[metadata_key(key)] = retr_meta ? retr_meta : ""
      elsif not key.eql?("/")
        metadata[key[0..-2]] = fetch_dir_metadata("#{id}#{key}", api_version)
      end
    end
    metadata
  end
end

#fetch_dynamic_data ⇒ Object 



180
181
182
183
184
185
186
187
188
189
190
 
# File 'lib/ohai/mixin/ec2_metadata.rb', line 180

def fetch_dynamic_data
  @fetch_dynamic_data ||= begin
    response = http_client.get("/#{best_api_version}/dynamic/instance-identity/document/")

    if json?(response.body) && response.code == "200"
      FFI_Yajl::Parser.parse(response.body)
    else
      {}
    end
  end
end

#fetch_json_dir_metadata(id, api_version) ⇒ Object 



154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
 
# File 'lib/ohai/mixin/ec2_metadata.rb', line 154

def fetch_json_dir_metadata(id, api_version)
  metadata = {}
  retrieved_metadata = metadata_get(id, api_version)
  if retrieved_metadata
    retrieved_metadata.split("\n").each do |o|
      key = expand_path(o)
      if key[-1..-1] != "/"
        retr_meta = metadata_get("#{id}#{key}", api_version)
        data = retr_meta ? retr_meta : ""
        json = String(data)
        parser = FFI_Yajl::Parser.new
        metadata[metadata_key(key)] = parser.parse(json)
      elsif not key.eql?("/")
        metadata[key[0..-2]] = fetch_json_dir_metadata("#{id}#{key}", api_version)
      end
    end
    metadata
  end
end

#fetch_metadata(id = "", api_version = nil) ⇒ Object 



107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
 
# File 'lib/ohai/mixin/ec2_metadata.rb', line 107

def fetch_metadata(id = "", api_version = nil)
  metadata = {}
  retrieved_metadata = metadata_get(id, best_api_version)
  if retrieved_metadata
    retrieved_metadata.split("\n").each do |o|
      key = expand_path("#{id}#{o}")
      if key[-1..-1] != "/"
        metadata[metadata_key(key)] =
          if EC2_ARRAY_VALUES.include? key
            retr_meta = metadata_get(key, best_api_version)
            retr_meta ? retr_meta.split("\n") : retr_meta
          else
            metadata_get(key, best_api_version)
          end
      elsif (not key.eql?(id)) && (not key.eql?("/"))
        name = key[0..-2]
        sym = metadata_key(name)
        if EC2_ARRAY_DIR.include?(name)
          metadata[sym] = fetch_dir_metadata(key, best_api_version)
        elsif EC2_JSON_DIR.include?(name)
          metadata[sym] = fetch_json_dir_metadata(key, best_api_version)
        else
          fetch_metadata(key, best_api_version).each { |k, v| metadata[k] = v }
        end
      end
    end
    metadata
  end
end

#fetch_userdata ⇒ Object 



174
175
176
177
178
 
# File 'lib/ohai/mixin/ec2_metadata.rb', line 174

def fetch_userdata
  logger.trace("Mixin EC2: Fetching http://#{EC2_METADATA_ADDR}/#{best_api_version}/user-data/")
  response = http_client.get("/#{best_api_version}/user-data/")
  response.code == "200" ? response.body : nil
end

#http_client ⇒ Net::HTTP

a net/http client with a timeout of 10s and a keepalive of 10s

Returns:

  • (Net::HTTP) 


79
80
81
82
83
84
 
# File 'lib/ohai/mixin/ec2_metadata.rb', line 79

def http_client
  @conn ||= Net::HTTP.start(EC2_METADATA_ADDR).tap do |h|
    h.read_timeout = 10
    h.keep_alive_timeout = 10
  end
end

#metadata_get(id, api_version) ⇒ Object

Get metadata for a given path and API version

Typically, a 200 response is expected for valid metadata. On certain instance types, traversing the provided metadata path produces a 404 for some unknown reason. In that event, return ‘nil` and continue the run instead of failing it.



92
93
94
95
96
97
98
99
100
101
102
103
104
105
 
# File 'lib/ohai/mixin/ec2_metadata.rb', line 92

def metadata_get(id, api_version)
  path = "/#{api_version}/meta-data/#{id}"
  logger.trace("Mixin EC2: Fetching http://#{EC2_METADATA_ADDR}#{path}")
  response = http_client.get(path)
  case response.code
  when "200"
    response.body
  when "404"
    logger.trace("Mixin EC2: Encountered 404 response retrieving EC2 metadata path: #{path} ; continuing.")
    nil
  else
    raise "Mixin EC2: Encountered error retrieving EC2 metadata (#{path} returned #{response.code} response)"
  end
end