How to check if SSH connection was established with AWS instance

Question

I'm trying to connect to the Amazon EC2 instance via SSH using `boto`. I know that ssh connection can be established after some time after instance was created. So my questions are: - Can I somehow check if SSH is up on the instance? (if so, how?) - Or how can I check for the output of `boto.manage.cmdshell.sshclient_from_instance()`? I mean for example if the output prints out `Could not establish SSH connection`, than try again. That's what I tried so far, but have no luck: ``` if instance.state == 'running': retry = True while retry: try: print 'Connecting to ssh' key_path = os.path.join(os.path.expanduser('~/.ssh'), 'secret_key.pem') cmd = boto.manage.cmdshell.sshclient_from_instance(instance, key_path, user_name='ec2-user') print instance.update() if cmd: retry = False except: print 'Going to sleep' time.sleep(10) SSH Connection refused, will retry in 5 seconds SSH Connection refused, will retry in 5 seconds SSH Connection refused, will retry in 5 seconds SSH Connection refused,…

Accepted Answer

The message "SSH Connection refused, will retry in 5 seconds" is coming from boto: http://code.google.com/p/boto/source/browse/trunk/boto/manage/cmdshell.py

Initially, 'running' just implicates that the instance has started booting. As long as `sshd` is not up, connections to port 22 are refused. Hence, what you observe is absolutely to be expected if `sshd` does not come up within the first 25 seconds of 'running' state.

Since it is not predictable when `sshd` comes up exactly and in case you do not want to waste time by just defining a constant long waiting period, you could implement your own polling code that in e.g. 1 to 5 second intervals checks if port 22 is reachable. Only if it is invoke `boto.manage.cmdshell.sshclient_from_instance()`.

A simple way to test if a certain TCP port of a certain host is reachable is via the `socket` module:

```
import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
try:
    s.connect(('hostname', 22))
    print "Port 22 reachable"
except socket.error as e:
    print "Error on connect: %s" % e
s.close()
```

How to check if SSH connection was established with AWS instance

Solution

Problem