Proxy device seemingly not forwarding traffic

LXD
1

Hi all,

I’m having an issue seeing traffic from a proxy device in the container.

To create the proxy device, I’m running the following command

lxc config device add mySqlServer port3306 proxy listen=tcp:0.0.0.0:33306 connect=tcp:127.0.0.1:3306

If I try to connect to port 33306 on the host machine, the following happens:

  • I see the network traffic in tcpdump on the host
  • I can see “Accepted a new connection” in /var/log/lxd/mySqlServer/proxy.port3306.log

What doesn’t happen is anything in the container. When running tcpdump, I see no network traffic, and I can’t connect to mysql (yes it is running and listening on 3306). netstat -tunap on the host shows 33306 listening and on the container shows 3306 listening.

I’m running on Ubuntu 18.04, and lxc version gives

Client version: 3.0.2
Server version: 3.0.2

Any suggestions would be greatly appreciated!

Thanks!

2

Hi!

I tried this myself and it worked fine for me. I used LXD 3.8 though.

Can you verify that you got the correct values for the part connect=tcp:127.0.0.1:3306? Both the loopback and port? If either is wrong, you get the error

ERROR 2013 (HY000): Lost connection to MySQL server at 'reading initial communication packet', system error: 2

Both telnet and mysql can be used to test the connection.

In the container you would run sudo tcpdump -i lo port 3306. You will not see any traffic in realtime due to buffering. You need to Ctrl+C to view the connection attempts.

3

You also have the alternative of sharing the Unix socket to the host.

4

Hey, thanks for getting back to me!

I’m going to try the first tcpdump test you suggested.

Also, when you say share the unix socket, can you expand on that?

5

Hmmm, well it seems that the traffic is going through to MySQL, but for some reason it’s denying the connection, and the problem seems to be MySQL itself, rather than LXC/D.

Also, one thing I found was if you include -l in the tcpdump command, it’ll output without buffering. For testing I was using the following:
tcpdump -l -A -nni lo port 3306

-A will show the packet in ASCII so you can see the packet contents/strings going back and forth.

So, @simos, thanks very much for the help, I do apprecaite it!