Python on GCE: connection failed because connected host has failed to respond

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I've been working on a project that requires a bit of networking between a server (hosted on GCE) and multiple clients. I created a Compute Engine Instance to run a Python script as shown in this video: https://www.youtube.com/watch?v=5OL7fu2R4M8.

Here is my server-side script:

server = socket.gethostbyname(socket.gethostname()) # 10.128.X.XXX which is the Internal IP
print(server)
port = 5555
clients = 0

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((server, port))

s.listen(2)
print("Waiting for connection...")

while True:
    conn, addr = s.accept()
    print("Connected to: ", addr)

    conn.send(str.encode(f"{clients}"))
    clients += 1

and here is my client side-script:

class Network:
    def __init__(self):
        self.client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.server = "10.128.0.2"
        self.port = 5555
        self.addr = (self.server, self.port)
        self.id = int(self.connect())

    def connect(self):
        self.client.connect(self.addr)
        return self.client.recv(2048).decode()

network = Network()
print(f"Connected as client {network.id}")

I know this script works because I have tested it with my computer being the server and 1 client, and another computer being the 2nd client. But when I use the GCE as the server, I get this error in the client script:

TimeoutError: [WinError 10060] A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond

Could this be because I am using the internal IP address and not the external?

After this, I tried changing the firewall settings (added 'python-socket') of the GCE and this is what they look like:

enter image description here

But the error still persists...

As answered by W_B, I tried to run these commands on my VM and got the following outputs:

enter image description here enter image description here

enter image description here

google-compute-engine firewall sockets networking python
1 Answers

From your description it's evident it's the connection problem.

First of all you have to check if the firewall rule you created is still there. If it's "too broad" and allows for very wide access then it might be removed automatically even without you knowing it. It's on you'r screenshot but check it again just to be sure.

If it's there select the protocol you're goint to be using (I assume it's TCP) - some protocols are always blocked by default by GCP (you can't change this) so creating a rule with "any protocol" allowed is risky. Also - put one or two target IP's (not all inside this VPC) - this is not a must but improves security of your network.

Second - make sure port 5555 you're trying to connect to is accessible from other computers. You can scan the target host with nmap -p 5554 put.server.ip.here

You can scan it from the Internet or other VM's in the same VPC network.

You should get something like this:

root@localhost:~$ nmap -p 443 192.168.1.6
Starting Nmap 7.70 ( https://nmap.org ) at 2020-06-25 17:12 UTC
Nmap scan report for 192.168.1.6
Host is up (0.00091s latency).

PORT    STATE SERVICE
443/tcp open  https

Nmap done: 1 IP address (1 host up) scanned in 0.04 seconds

If you see 5555/tcp filtered freeciv this means that something blocks the port.

Run nmap on the server (I assume you run some version of Linux) and if you don't want to install any non-essencial software you can use sudo netstat -tulpn | grep LISTEN to get a list of open ports (5555 should be on the list).

Also make sure firewall on your server doesn't block this port. You can use iptables for that.

user_122572500
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