Tidbit: The basics are Kinda Important, see also: Being Dumb with napalm-ansible

Hello friends!

This is a tiny post to remind you that the basics (and the obvious stuff!) is kinda important, or so it turns out! I was messing around using napalm-ansible to push templatized (templetized? template-ized?) configurations to some devices. Everything was going great until it wasn’t. Using Ansible template my configurations were looking good, but for whatever reason napalm-ansible kept timing out and leaving me with a nasty-gram like this:

"msg": "cannot install config: Search pattern never detected in send_command_expect: [>##]\\s*$"

Well then… that isn’t ideal clearly. The extra fun part was that if I ran the exact same Playbook again immediately after failure it would complete and everything would be great. I hate when you reboot a switch (or anything) and the thing you were troubleshooting works… this is kinda how this felt for me. So determined to get to the bottom of it I cloned my CSR a bajillion times and started testing.

I found this GitHub issue: https://github.com/ktbyers/netmiko/issues/555 where Kirk suggested setting the global delay factor. As I understand it this is there to basically just delay timeouts for things so that if the underlying napalm config merge was taking a long time for one or more configs we could gain some buffer time. I did this and originally set it to 2 as Kirk suggested, then I tried 4, and when that didn’t work I tried 20. Needless to say that took a *really* long time, but still eventually failed 😦

Doing as Kirk suggested in that same issue and manually doing the config replace didn’t really work since 1) I wasn’t doing a config replace, and 2) my configuration template did not contain management access stuff, so doing a merge would gut my connectivity (because it was a CSR I still had access via console but still).

Eventually, I realized I was just being a noob and not paying attention to the little obvious stuff we always overlook (because you would think it would just work). Turns out that the router I was poking had no public interweb access — why would this matter you may ask yourself? Of course if napalm/ansible can get to it, shouldn’t life be all rainbows and puppy dogs? Oh, one would think, but yours truly was doing a dumb thing and setting not one, but FOUR NTP servers to a DNS name. Yeah… without internet access that whole resolving DNS thing doesn’t work out so well. I have no idea what the timeouts were (and w/ the global delay set to 20 or whatever I used it took forever to timeout), but it clearly was angering things! Flipping those NTP servers to dummy IPs immediately solved my problem, duh 🙂

This has been your friendly public service reminder that it’s always something obvious and simple!

 

Advertisements

Python (relative) Imports and Unittests – Derp!

Been far too long since I wrote something. Spent way longer than I feel good about talking about derping around getting my ass kicked by some obvious shit so figured I should write it up as a reminder for me and to hopefully save some anonymous Internet person some heartache! Anyway, I’ve been meaning to put on my big boy pants and start actually writing test cases for all the Python code I write… I’ve been terrible at this and figured it’s time to get my life together with it. Rather than have a bunch of code that won’t really matter, I’ll just use ridiculously dumb examples here to get the issue and the “fix” (not being dumb!) across.

A pretty standard structure for a python project would look something like this:

mycoolproject/
├── mycoolproject
│   ├── __init__.py
│   ├── my_module_1.py
│   └── my_module_2.py
└── tests
 ├── __init__.py
 └── test_basics.py

You can see that we have our “project” — in this case named “mycoolproject” and within that directory we have a folder for our tests and a folder for the actual project code. In the root directory for our project we would probably have other stuff like a setup.py or a requirements.txt or whatever, but those things don’t matter for us at the moment. One last bit — we need those “__init__.py” files in there to make this a “project” — from the real Python docs:

“The __init__.py files are required to make Python treat the directories as containing packages; this is done to prevent directories with a common name, such as string, from unintentionally hiding valid modules that occur later on the module search path. In the simplest case, __init__.py can just be an empty file, but it can also execute initialization code for the package or set the __all__ variable, described later.”

You can find that doc here if you want to read some more about it.

Ok so now that we have the overall gist of things down, let’s take a look at our ridiculously over simplified “module”. Here is the contents of our file “my_module_1.py”:

my_string = 'whoa, this is so kewl'
print(my_string)

Pretty serious code 🙂

Our other script “my_module_2.py” is also pretty simple, but this one refers back to the first module to use the variable “my_string” — we’ll get to why this tripped me up in a bit:

import my_module_1
my_new_string = f'carl said: {my_module_1.my_string}'
print(f'carl said: {my_module_1.my_string}')

Alrighty, so if we run “my_module_1.py” it will simply print “whoa, this is so kewl” — no surprise there. If we run “my_module_2.py” it will *also* print “whoa, this is so kewl” because it is importing/loading the first script, and then of course it will also print “carl said: whoa, this is so kewl” as expected. Great, so our super fancy project works as desired. Now, because we are trying to be better about testing, let’s write a super simple test to validate this code works as expected.

In our test folder, we’ll create a new script called “test_basics.py” that looks like this:

import unittest
import my_module_1


class TestMe(unittest.TestCase):
   def test_stuff(self):
       assert my_module_1.my_string == 'whoa, this is so kewl'


if __name__ == '__main__':
    unittest.main()

At the top we’ll import the unittest library to use for our testing, and we’ll also import our script “my_module_1” so that we can validate (assert) that our variable “my_string” is actual equal to what we think it should be (“whoa, this is so kewl”).

So let’s go ahead and run our test suite and see what happens:

Carls-MacBook-Pro-2:mycoolproject Carl$ python3 -m unittest tests/test_basics.py
E
======================================================================
ERROR: test_basics (unittest.loader._FailedTest)
----------------------------------------------------------------------
ImportError: Failed to import test module: test_basics
Traceback (most recent call last):
 File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/loader.py", line 153, in loadTestsFromName
 module = __import__(module_name)
 File "/Users/Carl/Desktop/mycoolproject/tests/test_basics.py", line 2, in <module>
 import my_module_1
ModuleNotFoundError: No module named 'my_module_1'


----------------------------------------------------------------------
Ran 1 test in 0.000s

 

Well… not ideal eh? Obviously we have some kind of import error since Python is complaining it can’t find our module “my_module_1”. What gives? Well, we know that Python is mad at the line where we import “my_module_1” so obviously we need to start there. We also know that our modules actually run fine within their directory — they do exactly what we think they should. So with this information we can understand that Python — when ran from the tests directory has no idea how and where to find the module we are trying to run. This makes sense because when you think about it Python will search for modules in the local folder and the system path(s) — we can see where Python is looking by importing sys and printing out the path, let’s see what that looks like in our tests folder:

Carls-MacBook-Pro-2:tests Carl$ python3
 Python 3.6.4 (v3.6.4:d48ecebad5, Dec 18 2017, 21:07:28)
 [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
 Type "help", "copyright", "credits" or "license" for more information.
 >>> import sys
 >>> sys.path
 ['', '/Library/Frameworks/Python.framework/Versions/3.6/lib/python36.zip', '/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6', '/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/lib-dynload', '/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages']
 >>>

Ok, so we know it’s looking in the normal paths, and that very first entry (”) shows us its going to look for stuff locally too, but obviously nowhere to be seen is the module we’ve been building. So somehow we need to tell Python to look there, what happens if we ask Python to import “my_module_1” *from* “mycoolproject” like so:

from mycoolproject import my_module_1

Let’s run it and see what happens:

Carls-MacBook-Pro-2:mycoolproject Carl$ python3 -m unittest tests/test_basics.py
whoa, this is so kewl
.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

Hey that seems a lot better huh? Up to this point everything has been super straight forward and if you’ve done any amount of Python stuff you’ll be more than familiar with import errors as you’ve undoubtedly forgotten to import something and had this happen to you. The next bit is where I got tripped up… let’s add a quick test case to test our other Python file:

import unittest
from mycoolproject import my_module_1
from mycoolproject import my_module_2


class TestMe(unittest.TestCase):
   def test_stuff(self):
       assert my_module_1.my_string == 'whoa, this is so kewl'

  def test_other_stuff(self):
      assert my_module_2.my_new_string == 'carl said: whoa, this is so kewl'


if __name__ == '__main__':
    unittest.main()

Pretty straight forward stuff here too — we simply imported the other module and added a test case to assert that the string is what we think it should be. So what happens if we run our unit tests again?

Carls-MacBook-Pro-2:mycoolproject Carl$ python3 -m unittest tests/test_basics.py
whoa, this is so kewl
E
======================================================================
ERROR: test_basics (unittest.loader._FailedTest)
----------------------------------------------------------------------
ImportError: Failed to import test module: test_basics
Traceback (most recent call last):
 File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/loader.py", line 153, in loadTestsFromName
 module = __import__(module_name)
 File "/Users/Carl/Desktop/mycoolproject/tests/test_basics.py", line 3, in <module>
 from mycoolproject import my_module_2
 File "/Users/Carl/Desktop/mycoolproject/mycoolproject/my_module_2.py", line 1, in <module>
 import my_module_1
ModuleNotFoundError: No module named 'my_module_1'


----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (errors=1)

Annnnnnd we’re back to not working. So what gives? We get kinda the same error as before — complaining about import errors and whatnot. Not cool, especially since we basically did the same thing we did for “my_module_2” as we already did (and got working) for “my_module_1”. This time we can see that Python is upset about not finding a module called “my_module_1” — pretty ridiculous given the fact that importing that module is the second line of our test file right? BUT this is not failing *in* our test file — and here is what tripped me up. The issue is (and I’ll probably butcher the exact technical reasoning for this but you can check out this super handy SO post) that Python is confused about where that module is because the path for the execution (via unittest) is not *in* the same folder as the modules themselves. So we can address this by ensuring that the imports in our modules are not relative, but instead fully qualified if you will. Changing our “my_module_2” file to look like this:

from mycoolproject import my_module_1

my_new_string = f'carl said: {my_module_1.my_string}'
print(my_new_string)

Instead of importing from our local file we are now specifying the project that we are importing from, running our test again we get the following (good) results:

Carls-MacBook-Pro-2:mycoolproject Carl$ python3 -m unittest tests/test_basics.py
whoa, this is so kewl
carl said: whoa, this is so kewl
..
----------------------------------------------------------------------
Ran 2 tests in 0.000s

OK

TL;DR — pay attention to your imports, easy thing to fix but easy to miss it, run it locally and have everything run great and then be dumb like me and get angry at tests for not behaving the way you think they should 🙂