Develop Reference

How to determine if remote ESXI Host has booted fully?

I am writing a Python Script to fully boot up a handful of ESXI hosts remotely, and I am having trouble with determining when ESXI has finished booting and is ready to receive commands send over SSH. I am running the script on a windows host that is hardwired to each ESXI host and the system is air-gapped so there is no firewalls in the way and no security software would interfere.
Currently I am doing this: I remote into the chassis through SSH and send the power commands to the ESXI host - this works and has always worked. Then, I attempt to SSH into each blade and send the following command
esxcli system stats uptime get
The command doesn't matter, I just need a response to make sure that the host is up. Below is the function I am using to send the SSH commands in hopes of getting a response
def send_command(ip, port, timeout, retry_interval, cmd, user, password):
ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
retry_interval = float(retry_interval)
timeout = int(timeout)
timeout_start = time.time()
worked = False
while worked == False:
time.sleep(retry_interval)
try:
ssh.connect(ip, port, user, password, timeout=5)
stdin,stdout,stderr=ssh.exec_command(cmd)
outlines=stdout.readlines()
resp=''.join(outlines)
print(resp)
worked = True
return (resp)
except socket_error as e:
worked = False
print(e)
continue
except paramiko.ssh_exception.SSHException as e:
worked = False
# socket is open, but not SSH service responded
print(e)
continue
except TimeoutError as e:
print(e)
worked = False
pass
except socket.timeout as e:
print(e)
worked = False
continue
except paramiko.ssh_exception.NoValidConnectionsError as e:
print(e)
worked = False
continue
except socket.error as serr:
print(serr)
worked = False
continue
except IOError as e:
print(e)
worked = False
continue
except:
print(e)
worked = False
continue
My goal here is to catch all of the exceptions long enough for the host to finish booting and then receive a response. The issue is that sometimes it will loop for several minutes (as expected when booting a system like this), and then it will print
IO error: [Errno 111] Connection refused
And then drop out of the function/try catch block and never establish the connection. I know that this is a fault of my exceptions handling because when this happens, I stop the script, wait a few minutes, run it again without touching anything else and the esxcli command will work perfectly and the script will work great.
How do I prevent the Errno 111 error from breaking my loop? Any help is greatly appreciated
Edit: One possible duct tape solution could be changing the command to "esxcli system hostname get" and checking the response for the word "Domain". This might work because the IOError seems to be a response and not an exception, I'll have to wait until monday to test that solution though.

I solved it. It occured to me that I was handling all possible exceptions that any python code could possibly throw, so my defect wasn't a python error and that would make sense why I wasn't finding anything online about the relationship between Python, SSH and the Errno 111 error.
The print out is in fact a response from the ESXI host, and my code is looking for any response. So I simply changed the esxcli command from requesting the uptime to
esxcli system hostname get
and then through this into the function
substring = "Domain"
if substring not in resp:
print(resp)
continue
I am looking for the word "Domain" because that must be there if that call is successful.
How I figure it out: I installed ESXI 7 on an old Intel Nuc, turned on SSH in the kickstart script, started the script and then turned on the nuc. The reason I used the NUC is because a fresh install on simple hardware boots up much faster and quietly than Dell Blades! Also, I wrapped the resp variable in a print(type(OBJECT)) line and was able to determine that it was infact a string and not an error object.
This may not help someone that has a legitimate Errno 111 error, I knew I was going to run into this error each and everytime I ran the code and I just needed to know how to handle it and hold the loop until I got the response I wanted.
Edit: I suppose it would be easier to just filter for the world "errno" and then continue the loop instead of using a different substring. That would handle all of my use cases and eliminate the need for a different function.

psycopg2.OperationalError: SSL SYSCALL error: EOF detected

I was using psycopg2 in python script to connect to Redshift database and occasionally I receive the error as below:
psycopg2.OperationalError: SSL SYSCALL error: EOF detected
This error only happened once awhile and 90% of the time the script worked.
I tried to put it into a try and except block to catch the error, but it seems like the catching didn't work. For example, I try to capture the error so that it will automatically send me an email if this happens. However, the email was not sent when error happened. Below are my code for try except:
try:
conn2 = psycopg2.connect(host="localhost", port = '5439',
database="testing", user="admin", password="admin")
except psycopg2.Error as e:
print ("Unable to connect!")
print (e.pgerror)
print (e.diag.message_detail)
# Call check_row_count function to check today's number of rows and send
mail to notify issue
print("Trigger send mail now")
import status_mail
print (status_mail.redshift_failed(YtdDate))
sys.exit(1)
else:
print("RedShift Database Connected")
cur2 = conn2.cursor()
rowcount = cur2.rowcount
Errors I received in my log:
Traceback (most recent call last):
File "/home/ec2-user/dradis/dradisetl-daily.py", line 579, in
load_from_redshift_to_s3()
File "/home/ec2-user/dradis/dradisetl-daily.py", line 106, in load_from_redshift_to_s3
delimiter as ','; """.format(YtdDate, s3location))
psycopg2.OperationalError: SSL SYSCALL error: EOF detected
So the question is, what causes this error and why isn't my try except block catching it?

From the docs:
exception psycopg2.OperationalError
Exception raised for errors that are related to the database’s
operation and not necessarily under the control of the programmer,
e.g. an unexpected disconnect occurs, the data source name is not
found, a transaction could not be processed, a memory allocation error
occurred during processing, etc.
This is an error which can be a result of many different things.
slow query
the process is running out of memory
other queries running causing tables to be locked indefinitely
running out of disk space
firewall
(You should definitely provide more information about these factors and more code.)
You were connected successfully but the OperationalError happened later.
Try to handle these disconnects in your script:
Put the command you want to execute into a try-catch block and try to reconnect if the connection is lost.

Recently encountered this error. The cause in my case was the network instability while working with database. If network will became down for enough time that the socket detect the timeout you will see this error. If down time is not so long you wont see any errors.
You may control timeouts of Keepalive and RTO features using this code sample
s = socket.fromfd(conn.fileno(), socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
s.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPIDLE, 6)
s.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPINTVL, 2)
s.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPCNT, 2)
s.setsockopt(socket.IPPROTO_TCP, socket.TCP_USER_TIMEOUT, 10000)
More information you can find in this post

If you attach the actual code that you are trying to except it would be helpful. In your attached stack trace its : " File "/home/ec2-user/dradis/dradisetl-daily.py", line 106"
Similar except code works fine for me. mind you, e.pgerror will be empty if the error occurred on the client side, such as the error in my example. the e.diag object will also be useless in this case.
try:
conn = psycopg2.connect('')
except psycopg2.Error as e:
print('Unable to connect!\n{0}'.format(e))
else:
print('Connected!')

Maybe it will be helpful for someone but I had such an error when I've tried to restore backup to the database which has not sufficient space for it.

Python 3 Read data from URL [duplicate]

I have this simple minimal 'working' example below that opens a connection to google every two seconds. When I run this script when I have a working internet connection, I get the Success message, and when I then disconnect, I get the Fail message and when I reconnect again I get the Success again. So far, so good.
However, when I start the script when the internet is disconnected, I get the Fail messages, and when I connect later, I never get the Success message. I keep getting the error:
urlopen error [Errno -2] Name or service not known
What is going on?
import urllib2, time
while True:
try:
print('Trying')
response = urllib2.urlopen('http://www.google.com')
print('Success')
time.sleep(2)
except Exception, e:
print('Fail ' + str(e))
time.sleep(2)

This happens because the DNS name "www.google.com" cannot be resolved. If there is no internet connection the DNS server is probably not reachable to resolve this entry.
It seems I misread your question the first time. The behaviour you describe is, on Linux, a peculiarity of glibc. It only reads "/etc/resolv.conf" once, when loading. glibc can be forced to re-read "/etc/resolv.conf" via the res_init() function.
One solution would be to wrap the res_init() function and call it before calling getaddrinfo() (which is indirectly used by urllib2.urlopen().
You might try the following (still assuming you're using Linux):
import ctypes
libc = ctypes.cdll.LoadLibrary('libc.so.6')
res_init = libc.__res_init
# ...
res_init()
response = urllib2.urlopen('http://www.google.com')
This might of course be optimized by waiting until "/etc/resolv.conf" is modified before calling res_init().
Another solution would be to install e.g. nscd (name service cache daemon).

For me, it was a proxy problem.
Running the following before import urllib.request helped
import os
os.environ['http_proxy']=''
response = urllib.request.urlopen('http://www.google.com')

Skip Connection Interruptions (Site & BeautifulSoup)

I'm currently doing this with my script:
Get the body (from sourcecode) and search for a string, it does it until the string is found. (If the site updates.)
Altough, if the connection is lost, the script stops.
My 'connection' code looks something like this (This keeps repeating in a while loop every 20 seconds):
opener = urllib2.build_opener()
opener.addheaders = [('User-agent', 'Mozilla/5.0')]
url = ('url')
openUrl = opener.open(url).read()
soup = BeautifulSoup(openUrl)
I've used urllib2 & BeautifulSoup.
Can anyone tell me how I could tell the script to "freeze" if the connection is lost and look to see if the internet connection is alive? Then continue based on the answer.(So, to check if the script CAN connect, not to see if the site is up. If it does checkings this way, the script will stop with a bunch of errors.)
Thank you!

Found the solution!
So, I need to check the connection every LOOP, before actually doing stuff.
So I created this function:
def check_internet(self):
try:
header = {"pragma" : "no-cache"}
req = urllib2.Request("http://www.google.ro", headers=header)
response = urllib2.urlopen(req,timeout=2)
return True
except urllib2.URLError as err:
return False
And it works, tested it with my connection down & up!
For the other newbies wodering:
while True:
conn = check_internet('Site or just Google, just checking for connection.')
try:
if conn is True:
#code
else:
#need to make it wait and re-do the while.
time.sleep(30)
except: urllib2.URLError as err:
#need to wait
time.sleep(20)
Works perfectly, the script has been running for about 10 hours now and it handles errors perfectly! It also works with my connection off and shows proper messages.
Open to suggestions for optimization!

Rather than "freeze" the script, I would have the script continue to run only if the connection is alive. If it's alive, run your code. If it's not alive, either attempt to reconnect, or halt execution.
while keepRunning:
if connectionIsAlive():
run_your_code()
else:
reconnect_maybe()
One way to check whether the connection is alive is described here Checking if a website is up via Python
If your program "stops with a bunch of errors" then that is likely because you're not properly handling the situation where you're unable to connect to the site (for various reasons such as you not having internet, their website is down, etc.).
You need to use a try/except block to make sure that you catch any errors that occur because you were unable to open a live connection.
try:
openUrl = opener.open(url).read()
except urllib2.URLError:
# something went wrong, how to respond?

Python - try statement breaking urllib2.urlopen

I'm writing a program in Python that has to make a http request while being forced onto a direct connection in order to avoid a proxy. Here is the code I use which successfully manages this:
print "INFO: Testing API..."
proxy = urllib2.ProxyHandler({})
opener = urllib2.build_opener(proxy)
urllib2.install_opener(opener)
req = urllib2.urlopen('http://maps.googleapis.com/maps/api/geocode/json?address=blahblah&sensor=true')
returneddata = json.loads(req.read())
I then want to add a try statement around 'req', in order to handle a situation where the user is not connected to the internet, which I have tried like so:
try:
req = urllib2.urlopen('http://maps.googleapis.com/maps/api/geocode/json?address=blahblah&sensor=true')
except urllib2.URLError:
print "Unable to connect etc etc"
The trouble is that by doing that, it always throws the exception, even though the address is perfectly accessible & the code works without it.
Any ideas? Cheers.