Issue with TCP server - Nginx & Python (socketserver)

October 8, 2019 195 views
DigitalOcean Nginx Python
JavierTorres
By:
JavierTorres

Hi all,

I have been developing a TCP Server in python (socketserver framework), in order to receive data from a GPS tracking unit. It just needs the IP, Port and type of server TCP/UDP.

The problem is that the Server does not receive data, it receives some information, I will show you below:

(The server code is at the end of this question)

b'PROXY TCP4 190.130.120.61 10.46.0.5 7840 3000'
45
b'PROXY TCP4 190.130.120.61 10.46.0.5 11159 3000'
46

When I checked nginx error logs

$ sudo tail –F /var/log/nginx/error.log

2019/10/08 11:19:33 [error] 3569#3569: *559 connect() failed (111: Connection refused) while connecting to upstream, client: 191.156.38.225, server: 0.0.0.0:3000, upstream: "127.0.0.1:7077", bytes from/to client:0/0, bytes from/to upstream:0/0
2019/10/08 11:19:45 [error] 3569#3569: *561 connect() failed (111: Connection refused) while connecting to upstream, client: 191.156.44.76, server: 0.0.0.0:3000, upstream: "127.0.0.1:7077", bytes from/to client:0/0, bytes from/to upstream:0/0
2019/10/08 11:19:58 [error] 3569#3569: *563 connect() failed (111: Connection refused) while connecting to upstream, client: 191.156.43.39, server: 0.0.0.0:3000, upstream: "127.0.0.1:7077", bytes from/to client:0/0, bytes from/to upstream:0/0

So, it confirms that the data was not received

Then I decided to test the TCP server with another alternative, hence I used the following code in other machine.

HOST, PORT = "myDigitalOceanPublicIP", 3000
#HOST, PORT = "127.0.0.1", 7077 Testing in local machine

data = "DataFromOtherMachine"

# Create a socket (SOCK_STREAM means a TCP socket)
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
    # Connect to server and send data
    sock.connect((HOST, PORT))
    sock.sendall(bytes(data + "\n", "utf-8"))

    # Receive data from the server and shut down
    received = str(sock.recv(1024), "utf-8")

print("Sent:     {}".format(data))
print("Received: {}".format(received))

Unfortunatly, I got the next error:

Traceback (most recent call last):
  File "client.py", line 16, in <module>
    received = str(sock.recv(1024), "utf-8")
ConnectionResetError: [Errno 54] Connection reset by peer

I do not undestand why this is occuring, I also have edited the
/etc/nginx/nginx.conf file as follow:

stream {
    server {
      listen 0.0.0.0:3000;
      proxy_pass 127.0.0.1:7077;
      proxy_protocol on;
    }
}

I have allowed port 3000 using ufd command:
$sudo ufw allow 3000/tcp
$sudo ufw allow 3000

Thank you for your time reading my question, I will appreciate your help

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1 Answer
bobbyiliev MOD October 9, 2019

Hello,

First you need to make sure that your python script is actually listening on prot 7077. You can do that with the following command:

netstat -plant | grep 7077

If you can see the service there, then the problem is with the Nginx setup. I would recommend not making the changes to the /etc/nginx/nginx.conf file but to the /etc/nginx/sites-enabled/default. The file should look something like this:

server {
    listen 80 default_server;
    listen [::]:80 default_server;

    location / {
        proxy_pass 127.0.0.1:7077;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

Then after applying the changes run a config test:

nginx -t

And then if you get Syntax OK restart Nginx:

systemctl restart nginx

Let me know how it goes!
Regards,
Bobby

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