To provide a load-balanced front-end environment, NAS provides a load-balancing tool that can automatically select the least-loaded among the PFE systems when you log in. The system load is measured as a weighted function of disk, processor, and network loads.

To invoke the load balancer, log in via SSH using the special hostname pfe (or pfe.nas.nasa.gov) instead of a specific PFE. The following sections describe in more detail how to invoke the load balancer when you log into a PFE.

Logging into a PFE in Two Steps

If you normally log into a PFE in two steps (first logging into an SFE, then logging into a PFE), simply use the pfe hostname in the second step to invoke the load balancer, as follows:

your_local_system% ssh username@sfeX (or ssh username@sfeX.nas.nasa.gov)
sfeX% ssh username@pfe (or ssh username@pfe.nas.nasa.gov)

where sfeX represents sfe[6-8].

You can also log into the last PFE you connected to via a particular SFE, as follows:

your_local_system% ssh username@sfeX (or ssh username@sfeX.nas.nasa.gov)
sfeX% ssh username@pfe-last (or ssh username@pfe-last.nas.nasa.gov)

You will be prompted for a password on the PFE selected by the load balancer.

Notes:

• If you have any issues connecting to one of the four SFEs, try connecting to a different one.
• username is your NAS login name. If you have the same username for your local system and the NAS systems, you can omit username@ in the command line.

Logging into a PFE in One Step (Using SSH Passthrough)

If you normally log into a PFE using SSH Passthrough, follow these steps.

Before You Begin

Add the following entry in the ~/.ssh/config file of your local system.

Notes:

• In this entry, the ssh-balance command is used instead of the ssh-proxy command, which is typically used for SSH passthrough. See line 2 below.
• The entry specifies sfe6, but you can use any of the four SFEs (sfe[6-8]).

Host pfe pfe-last pfe.nas.nasa.gov pfe-last.nas.nasa.gov
ProxyCommand ssh sfe6.nas.nasa.gov /usr/local/bin/ssh-balance %h
HostKeyAlias pfe21.nas.nas.gov
HostbasedAuthentication no

Or, if you use different usernames on your local system and on NAS systems:

Host pfe pfe-last pfe.nas.nasa.gov pfe-last.nas.nasa.gov
ProxyCommand ssh username@sfe6.nas.nasa.gov /usr/local/bin/ssh-balance %h
HostKeyAlias pfe21.nas.nas.gov
HostbasedAuthentication no

First-Time Login

The first time you invoke the load balancer using SSH passthrough, you will need to add -o "StrictHostKeyChecking=ask" to populate the host key, as follows:

your_local_system% ssh -o "StrictHostKeyChecking=ask" pfe (or pfe.nas.nasa.gov) 

Subsequent Logins

Once the key is populated, you don't need to do it again the next time you log in. Simply run:

your_local_system% ssh pfe (or ssh pfe.nas.nasa.gov) 

To connect to the last PFE you connected to, run:

your_local_system% ssh pfe-last (or ssh pfe-last.nas.nasa.gov) 

Checking Which PFE the Load Balancer Will Select

You can find out which host will be selected by the load balancer, without actually logging in, by running the ssh-balance command with the -l option on any SFE or enclave system. For example:

sfeX% ssh-balance -l pfe

where sfeX represents sfe[6-8]. This command will return a fully-qualified PFE hostname.