Lambda function using paramiko SSH Client unable to connect to EC2 in the same subnet

Question

I am writing this lambda function that uses **paramiko.SSHClient()** to connect to an EC2 instance that is located in the same Account / VPC / subnet.

The connection method is using the old user and password authentication method (no pass key involved) because the EC2 prohibits other authentication methods.

The method call goes as follows:
```
    c = paramiko.SSHClient()
    c.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    c.connect(server, port, username=username, password=password, pkey=None)
```

It works without any error when I run the Python code from my own machine. But when I deploy the code to Lambda, it gives me "[Error 16] Device or resource busy".

```
[ERROR] OSError: [Errno 16] Device or resource busy
Traceback (most recent call last):
  File "/var/task/lambda_function.py", line 36, in lambda_handler
    c.connect(server, port, username=username, password=password, pkey=None)
  File "/var/task/paramiko/client.py", line 377, in connect
    to_try = list(self._families_and_addresses(hostname, port))
  File "/var/task/paramiko/client.py", line 202, in _families_and_addresses
    addrinfos = socket.getaddrinfo(
  File "/var/lang/lib/python3.12/socket.py", line 963, in getaddrinfo
    for res in _socket.getaddrinfo(host, port, family, type, proto, flags):END RequestId: ....
```

The messagem doesn´t seem to be a network error, but rather an OS Error (as the message implies).

It seems to me that when the error raises, the SSHClient hasn´t started the connection processes yet so, it suggests a memory or IO issue inside the lambda machines.

I´ve checked basic stuff (Security Groups, Outbound rules, permissions, etc.) and they are all OK. Also, if I change the "server" parameter and give them a fake server, the message is still the same. So it shows the message is not related to socket connection, but to OS resource.

matthew_d · Answer

Are you writing your function on a Linux system or with Docker? When you do `pip` install, the binaries installed will depend on your machine's OS and Python Lambda functions deployed with zip files use a managed runtime of Amazon Linux.

MTodoric · Answer

I'm having the same issue but with using ldap3, however receiving the same stacktrace. Focus should not be on paramiko or ldap3, but on a lower level at core python module: **socket**, because that's where it's failing - when running `socket.getaddrinfo`.

So why would that be a problem on AWS lambda? Are we receiving network? Is this something configuration related?
In my case, I've added lambda function to a VPC, so it should receive an IP address and everything.

Lambda function using paramiko SSH Client unable to connect to EC2 in the same subnet

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