[OOD-users] is nc/ncat an interactive app requirement?

[Jeremy Nicklas]

Hi Em,

I think the members at OSC are pretty busy with a fairly large downtime
currently, so I'll try to answer this. Good news is that it isn't due to a
problem with your implementation of the interactive Jupyter app. Back when
I wrote that portion of the code, I just forgot to document that netcat is
a requirement for Interactive Apps to work out of the box (I made the
incorrect assumption that it will exist in most standard installations).
The relevant snippet of code where netcat is used can be seen here:

https://github.com/OSC/ood_core/blob/a87f59ea9d24cdcbe505c9ab859bcb120bae9951/lib/ood_core/batch_connect/template.rb#L120-L126

In particular, netcat is used in a Bash function to determine if a port on
the compute node is being used. This is used to not only find available
ports for an interactive application server to listen on:

https://github.com/OSC/bc_example_jupyter/blob/94d29b4ba705cfe3b17df8ce78f584a4a2f986c5/template/before.sh.erb#L32-L33

but also to wait until the interactive application server is fully launched
and listening on this port before creating the "Connect to Jupyter" button
for the user to connect to:

https://github.com/OSC/bc_example_jupyter/blob/94d29b4ba705cfe3b17df8ce78f584a4a2f986c5/template/after.sh#L4-L12

In fact, it is this latter snippet of code where you are seeing the timeout
occur. That Bash function `port_used()` in the first link is failing to
detect any port in use without netcat installed.

You have a few options to choose from for resolving this, take your pick:

- install netcat on the compute nodes (easiest)
- override the Bash function `port_used()` in your `template/before.sh.erb`
script before the `find_port` function is called with your own
implementation that doesn't use netcat (medium difficulty, note that it
isn't documented but there is a way to make this a global override for all
interactive apps)
- remove the timeout conditional in the `template/after.sh` script and just
sleep an appropriate amount of time until you are sure the interactive
server is running (easy, but possibly bad user experience)

-Jeremy Nicklas


On Thu, Oct 25, 2018 at 10:08 AM E.M. Dragowsky via OOD-users <
ood-users at lists.osc.edu> wrote:

> Greetings --
>
> In implementation of the Jupyter app, I have indications that nc is
> necessary for connections to compute nodes. The install documentation
> indicates that it may be used to test that reverse proxy connections are
> successfully configured (3.3 Verify it works)
>
> The compute nodes in our cluster (rhel7) do not have the 'nmap-ncat'
> package installed. When the package is installed, connections succeed.
> Without the package -- the connection times-out.
>
> I've done this on a subset of our nodes, and am preparing a 'change
> request' to have the 'nmap-ncat' package installed on all the nodes. Please
> let me know if I am only seeing part of the picture, or if what I describe
> indicates other problems with my implementation of the interactive jupyter
> app.
>
> Thanks,
> ~ Em
>
> --
> E.M. Dragowsky, Ph.D.
> Research Computing -- UTech
> Case Western Reserve University
> (216) 368-0082
> _______________________________________________
> OOD-users mailing list
> OOD-users at lists.osc.edu
> https://lists.osu.edu/mailman/listinfo/ood-users
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osu.edu/pipermail/ood-users/attachments/20181025/acabba57/attachment.html>