added soa nameserver validator

app/jobs/validate_dnssec_job.rb

@@ -32,6 +32,10 @@ class ValidateDnssecJob < ApplicationJob
 
   def iterate_nameservers(domain)
     domain.nameservers.each do |n|
+      result_nameserver_validation = SoaNameserverQuery.validate(domain_name: domain.name, hostname: n.hostname)
+
+      return unless result_nameserver_validation
+
       validate(hostname: n.hostname, domain: domain)
 
       notify_contacts(domain)

app/services/soa_nameserver_query.rb

@@ -0,0 +1,49 @@
+module SoaNameserverQuery
+  include Dnsruby
+
+  extend self
+
+  def validate(domain_name:, hostname:)
+
+      resolver = create_resolver(hostname)
+
+      answers = resolver.query(domain_name, 'SOA', 'IN')
+      answers.answer.each do |a|
+
+        if a.serial.nil?
+          logger.info "No serial number of nameserver found"
+
+          return false
+        end
+
+        serial_number = a.serial.to_s
+
+        p "-------------- >>"
+        p "serial number #{serial_number} of #{hostname} - domain name: #{domain_name}"
+        p "<< --------------"
+        true
+      end
+
+  rescue StandardError => e
+    logger.error e.message
+    logger.error "failed #{hostname} validation of #{domain_name} domain name"
+
+    false
+  end
+
+  private
+
+  def create_resolver(nameserver)
+    resolver = Dnsruby::Resolver.new
+    resolver.retry_times = 3
+    resolver.recurse = 0  # Send out non-recursive queries
+    # disable caching otherwise SOA is cached from first nameserver queried
+    resolver.do_caching = false
+    resolver.nameserver = nameserver
+    resolver
+  end
+
+  def logger
+    @logger ||= Rails.logger
+  end
+end