Druby using just IP addresses

Ruby
1

Hi

I’d like to use druby, but with the client using just an IP address to
contact the server, and vice versa. The initial connection works fine,
but then it seems the server can’t find the client to send a reply when
a method is invoked.

I realise this question has been asked before, and answered by ‘fix your
DNS’ or ‘tweak etc/hosts’.

However, this is for an end-user app, so most users (of clients and
servers) won’t be permitted to access etc/hosts, even if I wanted to
explain what they should do to it.

So

  • has anyone hacked drb to work without hostnames?
  • failing that, is there a deep technical reason that using IP addresses
    only will never work and I shouldn’t bother even trying? It seems lots
    of other net applications work fine without caring that DNS is fixed,
    but I’ve not got masses of experience with socket programming in Ruby.

thanks
alex

2

Alex F. wrote:

explain what they should do to it.

So

  • has anyone hacked drb to work without hostnames?
  • failing that, is there a deep technical reason that using IP addresses
    only will never work and I shouldn’t bother even trying? It seems lots
    of other net applications work fine without caring that DNS is fixed,
    but I’ve not got masses of experience with socket programming in Ruby.

Probably someone has suggested this before, but have you tried

Socket.do_not_reverse_lookup = true

?

3

On 10/4/06, Alex F. [email protected] wrote:

  • failing that, is there a deep technical reason that using IP addresses only will never work and I shouldn’t bother even trying? It seems lots of other net applications work fine without caring that DNS is fixed, but I’ve not got masses of experience with socket programming in Ruby.
    I’m not sure what isn’t working for you with out some code. I do have
    an idea though this seems to work for me:

Server’s irb session:

require ‘drb’
=> true
DRb.start_service(‘druby://192.168.0.104:1234’, “abc”)
=> #<DRb::DRbServer …>

Client’s session:

require ‘drb’
=> true
DRb.start_service(‘druby://192.168.0.101:1234’)
=> DRb::DRbServer …>
remote = DRbObject.new(nil, ‘druby://192.168.0.104:1234’)
=> #<DRb::DRbObject …>
remote.to_s # Force display
=> “abc”
remote.size
=> 3
remote.replace(“ruby”)
=> #<DRb::DRbObject …>
remote.to_s
=> “ruby”
remote.size
=> 4

Note that it is a good idea to specify an explicit interface on the
client side so you make sure it binds to something the server can
reach. Some systems will bind to something like 127.0.0.1 when
resolving the host’s name (i.e. Ubuntu does this). The two way channel
is vital to have DRb work reliably in most cases (unmarshalled objects
can be referenced in both directions).

Brian.

4

Brian M. wrote:

programming in Ruby.
Note that it is a good idea to specify an explicit interface on the
client side so you make sure it binds to something the server can
reach. Some systems will bind to something like 127.0.0.1 when
resolving the host’s name (i.e. Ubuntu does this). The two way channel
is vital to have DRb work reliably in most cases (unmarshalled objects
can be referenced in both directions).

Adding to that: it might well be that you are trying to do things in
environments that simply won’t permit this. If your client is behind a
firewall / router with NAT and the server tries to open a connection to
the client system that’s often not permitted. So, in order to get this
to work in these environments someone must actually change FW config.

Kind regards

robert
5

Brian M. wrote:

On 10/4/06, Alex F. [email protected] wrote:

Hi

I’d like to use druby, but with the client using just an IP address to
contact the server, and vice versa

Note that it is a good idea to specify an explicit interface on the
client side so you make sure it binds to something the server can
reach. Some systems will bind to something like 127.0.0.1 when
resolving the host’s name (i.e. Ubuntu does this).

Thank you, that was it. Added an explicit IP address on the client side
made it work fine.

I was using start_service on the client with no args. It was binding to
the windows machine name, and the OS X server I was trying to connect to
couldn’t resolve it back.

alex

6

On Oct 4, 2006, at 10:50 AM, Alex F. wrote:

So

  • has anyone hacked drb to work without hostnames?

DRb uses Socket.gethostname to determine the hostname. If you don’t
otherwise use this method just override it to return an IP address.

  • failing that, is there a deep technical reason that using IP
    addresses only will never work and I shouldn’t bother even trying?
    It seems lots of other net applications work fine without caring
    that DNS is fixed, but I’ve not got masses of experience with
    socket programming in Ruby.

Most programs aren’t servers that are running on arbitrary machines
having other arbitrary machines connecting back to them.

One solution would be adding socket multiplexing in place of
launching servers.

–
Eric H. - [email protected] - http://blog.segment7.net
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