Class: Puppet::HTTP::DNS

Inherits:
Object show all
Defined in:
lib/puppet/http/dns.rb

Defined Under Namespace

Classes: CacheEntry

Instance Method Summary collapse

Constructor Details

#initialize(resolver = Resolv::DNS.new) ⇒ DNS

Returns a new instance of DNS.



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# File 'lib/puppet/http/dns.rb', line 27

def initialize(resolver = Resolv::DNS.new)
  @resolver = resolver

  # Stores DNS records per service, along with their TTL
  # and the time at which they were resolved, for cache
  # eviction.
  @record_cache = {}
end

Instance Method Details

#each_srv_record(domain, service_name = :puppet, &block) ⇒ Object

Iterate through the list of records for this service and yield each server and port pair. Records are only fetched via DNS query the first time and cached for the duration of their service’s TTL thereafter.



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# File 'lib/puppet/http/dns.rb', line 43

def each_srv_record(domain, service_name = :puppet, &block)
  if domain.nil? or domain.empty?
    Puppet.debug "Domain not known; skipping SRV lookup"
    return
  end

  Puppet.debug "Searching for SRV records for domain: #{domain}"

  case service_name
  when :puppet then service = '_x-puppet'
  when :file   then service = '_x-puppet-fileserver'
  else              service = "_x-puppet-#{service_name}"
  end
  record_name = "#{service}._tcp.#{domain}"

  if @record_cache.has_key?(service_name) && !expired?(service_name)
    records = @record_cache[service_name].records
    Puppet.debug "Using cached record for #{record_name}"
  else
    records = @resolver.getresources(record_name, Resolv::DNS::Resource::IN::SRV)
    if records.size > 0
      @record_cache[service_name] = CacheEntry.new(records)
    end
    Puppet.debug "Found #{records.size} SRV records for: #{record_name}"
  end

  if records.size == 0 && service_name != :puppet
    # Try the generic :puppet service if no SRV records were found
    # for the specific service.
    each_srv_record(domain, :puppet, &block)
  else
    each_priority(records) do |recs|
      while next_rr = recs.delete(find_weighted_server(recs)) # rubocop:disable Lint/AssignmentInCondition
        Puppet.debug "Yielding next server of #{next_rr.target}:#{next_rr.port}"
        yield next_rr.target.to_s, next_rr.port
      end
    end
  end
end

#expired?(service_name) ⇒ Boolean

Checks if the cached entry for the given service has expired.



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# File 'lib/puppet/http/dns.rb', line 128

def expired?(service_name)
  entry = @record_cache[service_name]
  if entry
    Time.now > (entry.resolution_time + entry.ttl)
  else
    true
  end
end

#find_weighted_server(records) ⇒ Resolv::DNS::Resource::IN:SRV

Given a list of records of the same priority, chooses a random one from among them, favoring those with higher weights.



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# File 'lib/puppet/http/dns.rb', line 88

def find_weighted_server(records)
  return nil if records.nil? || records.empty?
  return records.first if records.size == 1

  # Calculate the sum of all weights in the list of resource records,
  # This is used to then select hosts until the weight exceeds what
  # random number we selected.  For example, if we have weights of 1 8 and 3:
  #
  # |-|--------|---|
  #        ^
  # We generate a random number 5, and iterate through the records, adding
  # the current record's weight to the accumulator until the weight of the
  # current record plus previous records is greater than the random number.
  total_weight = records.inject(0) { |sum, record|
    sum + weight(record)
  }
  current_weight = 0
  chosen_weight  = 1 + Kernel.rand(total_weight)

  records.each do |record|
    current_weight += weight(record)
    return record if current_weight >= chosen_weight
  end
end

#ttl(service_name) ⇒ Integer

Returns TTL for the cached records for this service.



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# File 'lib/puppet/http/dns.rb', line 120

def ttl(service_name)
  @record_cache[service_name].ttl
end

#weight(record) ⇒ Object 



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# File 'lib/puppet/http/dns.rb', line 113

def weight(record)
  record.weight == 0 ? 1 : record.weight * 10
end