anchor.diff:  
       # registering route 53 hostnames if any:
       echo ${concatStringsSep " " (
  -        mapAttrsToList (_: args: register-hostname {
  +        mapAttrsToList (_: args: retry-wrapper (register-hostname {
            zone = args.name;
            inherit (args) zoneId iamCredentialName useLocalHostname;
  -       }) config.ec2.route53RegisterHostname)} | ${xargs} -n1 -P2 ${bash}
  +       })) config.ec2.route53RegisterHostname)} | ${xargs} -n1 -P2 ${bash}
   
       ${optionalString (!config.ec2.metadata) ''
       ip route add blackhole 169.254.169.254/32
  
positive.code:     hostname=$(${hostname}).${zone}
      record_value=$(${wget} http://169.254.169.254/latest/meta-data/${query})
  
      ${retry} ${curl-nofail} -d @/dev/stdin \
            -H "Content-Type: text/xml" \
            -H "x-amz-date: $date" \
            -H "$auth_header" \
  
negative.code:   bash = "${pkgs.bash}/bin/bash";
    xargs = "${pkgs.findutils}/bin/xargs";
  
    retry-wrapper = script: pkgs.writeScript "retry-${script.name}" ''
      ${retry} ${script}
    '';
  
    register-hostname = {
      zoneId, zone, iamCredentialName,
      useLocalHostname,
      query ? if useLocalHostname then "local-ipv4" else "public-hostname",
      recordType ? if useLocalHostname then "A" else "CNAME"
    }: pkgs.writeScript "ec2-register-hostname-${zone}" ''
      #!${bash}
      date=$(${curl} -I https://route53.amazonaws.com/date | ${awk} '/^Date: / {sub("Date: ", "", $0); sub("\\r", "", $0); print $0}')
  
      iam="${iamCredentialName}"
  