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 ⇒ String

The latest metadata version in EC2_SUPPORTED_VERSIONS that this instance supports in AWS supported metadata versions are determined at instance start so we need to be cautious here in case an instance has been running for a long time

Returns:



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# File 'lib/ohai/mixin/ec2_metadata.rb', line 84

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("/", { 'X-aws-ec2-metadata-token': v2_token })
    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 



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# File 'lib/ohai/mixin/ec2_metadata.rb', line 188

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 || ""
      elsif !key.eql?("/")
        metadata[key[0..-2]] = fetch_dir_metadata("#{id}#{key}", api_version)
      end
    end
    metadata
  end
end

#fetch_dynamic_data ⇒ Object 



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# File 'lib/ohai/mixin/ec2_metadata.rb', line 231

def fetch_dynamic_data
  @fetch_dynamic_data ||= begin
    response = http_client.get("/#{best_api_version}/dynamic/instance-identity/document/", { 'X-aws-ec2-metadata-token': v2_token })

    if response.code == "200"
      json_data = parse_json(response.body, {})
      if json_data.nil?
        logger.warn("Mixin Ec2Metadata: Metadata response is NOT valid JSON")
      end
      json_data
    else
      logger.warn("Mixin Ec2Metadata: Received response code #{response.code} requesting metadata")
      {}
    end
  end
end

#fetch_json_dir_metadata(id, api_version) ⇒ Object 



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# File 'lib/ohai/mixin/ec2_metadata.rb', line 205

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 || ""
        json = String(data)
        parser = FFI_Yajl::Parser.new
        metadata[metadata_key(key)] = parser.parse(json)
      elsif !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 



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# File 'lib/ohai/mixin/ec2_metadata.rb', line 158

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 (!key.eql?(id)) && (!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 



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# File 'lib/ohai/mixin/ec2_metadata.rb', line 225

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/", { 'X-aws-ec2-metadata-token': v2_token })
  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) 


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# File 'lib/ohai/mixin/ec2_metadata.rb', line 113

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.



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# File 'lib/ohai/mixin/ec2_metadata.rb', line 143

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, { 'X-aws-ec2-metadata-token': v2_token })
  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

#v2_token ⇒ NilClass, String

Fetch an API token for use querying AWS IMDSv2 or return nil if no token if found AWS like systems (think OpenStack) will not respond with a token here

Returns:

  • (NilClass, String) —

    API token or nil



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# File 'lib/ohai/mixin/ec2_metadata.rb', line 126

def v2_token
  @v2_token ||= begin
      request = http_client.put("/latest/api/token", nil, { 'X-aws-ec2-metadata-token-ttl-seconds': "60" })
      if request.code == "404" # not on AWS
        nil
      else
        request.body
      end
    end
end