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There is an HTCondor machine which is a submit node or an execute node, and you would like to share your new computer resources with others outside your department or division. But, you do not want crooks using your systems to wreak havoc. So, there is a firewall between your HTCondor resource and the Internet. Assume that the firewall is a separate host from the HTCondor resource. It is a bastion host running Linux, and the firewall is iptables, with Network Address Translation (NAT). This assumption allows the description to include explicit commands to run. You or your firewall administrator should translate these instructions to your particular firewall installation. We are also assuming that you are not going to be using CCB. CCB allows communication between HTCondor daemons in a private network (outgoing connections only) with daemons in a public network (bidirectional connections allowed). It therefore is not a complete solution for a case where you need daemons in two separate private networks to communicate---one or the other network must allow bidirectional connections for CCB to help. In the case described below, we want a submit node, which is in a private network, to communicate with execute nodes in other private networks, such as Open Science Grid. This is the private-to-private case that cannot be solved with CCB alone. The solution below uses port-forwarding to make the submit node effectively public. This allows the execute nodes in the remote private network to use CCB to have bidirectional connectivity with your submit node. Bidirectional connectivity could also be achieved without CCB by also applying the port-forwarding solution below to the execute nodes of the remote private network, which may not be possible, either because of your own security concerns or because you do not administer machines on the remote network.
Let us first assume that you have HTCondor installed and running. For this, you should follow the instructions in section 3.2 of the HTCondor manual.
Let us assume you have the following setup. The HTCondor schedd is installed on a machine (named S) with IP address 192.168.0.1; this is your submit machine. An HTCondor startd is installed on a machine (named E) at 192.168.0.2; this is your execute node. The firewall has an external---that is, facing the Internet---IP address of 10.0.0.1, and an internal---that is, facing toward your local network---IP address of 192.168.0.250; we will call this machine F. We know 10.0.0.1 is actually not a routable address, but pretend that it is for the duration of this document. S and E are in the domain mydomain.net
.
Then we will make the following changes to condor_config.local
on S (the schedd). To find your HTCondor configuration files, the command condor_config_val -dump
will be a big help, as the files are listed in the header of the output
USE_SHARED_PORT = True SHARED_PORT_ARGS = -p 9617 PRIVATE_NETWORK_NAME = mydomain.net PRIVATE_NETWORK_INTERFACE = eth0 TCP_FORWARDING_HOST = 10.0.0.1
TCP_FORWARDING_HOST
must match the external address of the collector.
On the execute node E, we have similar configuration changes, except for the shared port:
USE_SHARED_PORT = True SHARED_PORT_ARGS = -p 9616 PRIVATE_NETWORK_NAME = mydomain.net PRIVATE_NETWORK_INTERFACE = eth0 TCP_FORWARDING_HOST = 10.0.0.1
PRIVATE_NETWORK_NAME
on S and E allow them to communicate directly without going through the firewall F. The port choice of 9616 is arbitrary.
Now, on the firewall F, we run the following commands to redirect connections from the Internet to ports 9617 and 9616 on F to the corresponding ports on S and E:
iptables -t nat -A PREROUTING -p tcp -d 10.0.0.1 --dport 9617 -j DNAT --to-destination 192.168.0.1 iptables -t nat -A PREROUTING -p tcp -d 10.0.0.1 --dport 9616 -j DNAT --to-destination 192.168.0.2 iptables -A POSTROUTING -o eth1 -j SNAT --to-source 10.0.0.1
Finally, run condor_reconfig
on S and E to incorporate the configuration changes.
One may well ask how this works for HTCondor. Simply put, HTCondor wraps all the information in an string with all the address information. condor_status -schedd -l
will return a Schedd ClassAd, which will contain a line that looks something like:
MyAddress = "<10.0.0.1:9617?PrivAddr=%3c192.168.0.1:9617%3fsock%3d936_480b_8%3e&PrivNet=mydomain.net&noUDP&sock=936_480b_8>"