(maint) Refactor cloud dns

Moved the creation and deletion methods to a vmpooler class, to be used by the ec2
provisioner.
Added a check for failed deletion attempts, they are now retried up to 30 times

lib/vmpooler/cloud_dns.rb

@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+require 'googleauth'
+require 'google/cloud/dns'
+
+module Vmpooler
+  class PoolManager
+    class CloudDns
+      def initialize(project, dns_zone_resource_name)
+        @dns ||= Google::Cloud::Dns.new(project_id: project)
+        @dns_zone_resource_name = dns_zone_resource_name
+      end
+
+      def dns_create_or_replace(created_instance)
+        dns_zone = @dns.zone(@dns_zone_resource_name) if @dns_zone_resource_name
+        return unless dns_zone && created_instance && created_instance['name'] && created_instance['ip']
+
+        name = created_instance['name']
+        begin
+          change = dns_zone.add(name, 'A', 60, [created_instance['ip']])
+          debug_logger("#{change.id} - #{change.started_at} - #{change.status} DNS address added") if change
+        rescue Google::Cloud::AlreadyExistsError => _e
+          # DNS setup is done only for new instances, so in the rare case where a DNS record already exists (it is stale) and we replace it.
+          # the error is Google::Cloud::AlreadyExistsError: alreadyExists: The resource 'entity.change.additions[0]' named 'instance-8.test.vmpooler.net. (A)' already exists
+          change = dns_zone.replace(name, 'A', 60, [created_instance['ip']])
+          debug_logger("#{change.id} - #{change.started_at} - #{change.status} DNS address previously existed and was replaced") if change
+        end
+      end
+
+      def dns_teardown(created_instance)
+        dns_zone = @dns.zone(@dns_zone_resource_name) if @dns_zone_resource_name
+        return unless dns_zone && created_instance
+
+        retries = 0
+        name = created_instance['name']
+        change = dns_zone.remove(name, 'A')
+        debug_logger("#{change.id} - #{change.started_at} - #{change.status} DNS address removed") if change
+      rescue Google::Cloud::FailedPreconditionError => e
+        # this error was experienced intermittently, will retry to see if it can complete successfully
+        # the error is Google::Cloud::FailedPreconditionError: conditionNotMet: Precondition not met for 'entity.change.deletions[1]'
+        debug_logger("DNS teardown failed, retrying error: #{e}")
+        sleep 5
+        retry if (retries += 1) < 30
+      end
+
+      # used in local dev environment, set DEBUG_FLAG=true
+      # this way the upstream vmpooler manager does not get polluted with logs
+      def debug_logger(message, send_to_upstream: false)
+        # the default logger is simple and does not enforce debug levels (the first argument)
+        puts message if ENV['DEBUG_FLAG']
+        logger.log('[g]', message) if send_to_upstream
+      end
+    end
+  end
+end