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Various improvements to the SNMP forwarding/proxying container setup #2637

Merged
merged 8 commits into from Jun 5, 2023
Merged

Various improvements to the SNMP forwarding/proxying container setup #2637

merged 8 commits into from Jun 5, 2023

Commits on May 31, 2023

  1. Make signals propagate to remote socat process 

    This ensures that the remote socat process is torn down when the
forwarding container exits. Before this change, the socat process would
linger forever, causing the forwarding port to stay bound forever on the
remote hop-host.  Any subsequent attempts to restart the forwarding
container would just result in an error that looked like this:

```
socat[10092] E bind(5, {AF=2 0.0.0.0:10000}, 16): Address already in use
```

Using the `-tt` option to ssh forces SSH to allocate a pseudo-terminal,
even if the controlling process isn't attached to a real terminal.
Using the pseudo-terminal ensures that signals are propagated from the
ssh process to the socat process started on the remote, so when the SSH
session dies, socat will also.

We also drop the `-f` option, since that would cause the SSH process to
send the termination signal as soon as it forks and exits.  This uses
the shell to background the ssh process instead.
    @lunkwill42
    lunkwill42 committed May 31, 2023
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  2. Factor out local tunnel to a function 

    This factors out the setup of the local socat tunnel to a function,
backgrounds it and waits for all backgrounded processes to terminate.
    @lunkwill42
    lunkwill42 committed May 31, 2023
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  3. Stop container if any forwarding subprocess dies 

    This ensures the whole process group, and thereby the forwarding
container itself, dies if any of the forwarding subprocesses exit.

This should be a very explicit failure signal to the developer using
this forwarding container.
    @lunkwill42
    lunkwill42 committed May 31, 2023
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  4. Document that port needs to be free on hop-host

    @lunkwill42
    lunkwill42 committed May 31, 2023
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  5. Echo/log remote tunnel setup 

    It's nice to know what's going on, even if -x isn't used.
    @lunkwill42
    lunkwill42 committed May 31, 2023
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  6. Set specific ssh ConnectTimeout 

    For some weird reason, my SSH connection will not be properly
established unless I add an explicit ConnectTimout option.
    @lunkwill42
    lunkwill42 committed May 31, 2023
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  7. Support SNMP agents on IPv6 

    This ensures a remote IPv6 SNMP agent can be reached also, even if the
local address is still IPv4.
    @lunkwill42
    lunkwill42 committed May 31, 2023
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  8. Move cache-busting COPY to end of Dockerfile 

    Rebuilding much of the docker image just because the shell script is
changing is tiresome. This ensures the last thing that happpens is the
copying of the shell script.
    @lunkwill42
    lunkwill42 committed May 31, 2023
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