Copyright @ Lenovo US

Why do we want to build Python2 charms? Charms are claimed to built for Python3. However, the catch is that charms are also built for Ubuntu ecosystems ONLY if you care to examine its code base.

Take __init__.py in charmhelpers/charmhelpers for example:

try:
    import six  # flake8: noqa
except ImportError:
    if sys.version_info.major == 2:
        subprocess.check_call(['apt-get', 'install', '-y', 'python-six'])
    else:
        subprocess.check_call(['apt-get', 'install', '-y', 'python3-six'])
    import six  # flake8: noqa

Command line apt-get is a clue, isn't it? There are many such hardcoded lines who shout out that Ubuntu is the way to go, and of course, charms are developed by Canonical, and you are expected to use them the way they were designed for.

Well, this is fine until you want to deploy them on CentOS.

CentOS challenge

CentOS and RHEL remain to dominate enterprise. CentOS7 is shipped with Python27. We enabled EPEL-RELEASE repo, but then charm install gave us an error no module yum found. The call is made in charmhelpers/fetch.centos.py, and python34 has no yum module!

import yum

And trace it one step further, it came from charm-helpers/charmhelpers/fetch/__init__.py:

if __platform__ == "ubuntu":
    apt_cache = fetch.apt_cache
    apt_install = fetch.install
    apt_update = fetch.update
    apt_upgrade = fetch.upgrade
    apt_purge = fetch.purge
    apt_mark = fetch.apt_mark
    apt_hold = fetch.apt_hold
    apt_unhold = fetch.apt_unhold
    get_upstream_version = fetch.get_upstream_version
elif __platform__ == "centos":
    yum_search = fetch.yum_search

Here we are making a mapping between defined function definitions and the function names that will be used in other places in the lib. Needless to say, CentOS definitions are missing a lot comparing to Ubuntu's. So yes, import yum is just the tip of the iceberg, execution will break anywhere apt_ is called. Take apt_install for example, here is a search result where this function is expected:

-*- mode: grep; default-directory: "~/workspace/wss/hack/charmhelpers-0.15.0/" -*-
Grep started at Sat May 27 22:32:10

find . -type d \( -path \*/SCCS -o -path \*/RCS -o -path \*/CVS -o -path \*/MCVS -o -path \*/.src -o -path \*/.svn -o -path \*/.git -o -path \*/.hg -o -path \*/.bzr -o -path \*/_MTN -o -path \*/_darcs -o -path \*/\{arch\} \) -prune -o \! -type d \( -name .\#\* -o -name \*.beam -o -name \*.vee -o -name \*.jam -o -name \*.hi -o -name \*.o -o -name \*\~ -o -name \*.bin -o -name \*.lbin -o -name \*.so -o -name \*.a -o -name \*.ln -o -name \*.blg -o -name \*.bbl -o -name \*.elc -o -name \*.lof -o -name \*.glo -o -name \*.idx -o -name \*.lot -o -name \*.fmt -o -name \*.tfm -o -name \*.class -o -name \*.fas -o -name \*.lib -o -name \*.mem -o -name \*.x86f -o -name \*.sparcf -o -name \*.dfsl -o -name \*.pfsl -o -name \*.d64fsl -o -name \*.p64fsl -o -name \*.lx64fsl -o -name \*.lx32fsl -o -name \*.dx64fsl -o -name \*.dx32fsl -o -name \*.fx64fsl -o -name \*.fx32fsl -o -name \*.sx64fsl -o -name \*.sx32fsl -o -name \*.wx64fsl -o -name \*.wx32fsl -o -name \*.fasl -o -name \*.ufsl -o -name \*.fsl -o -name \*.dxl -o -name \*.lo -o -name \*.la -o -name \*.gmo -o -name \*.mo -o -name \*.toc -o -name \*.aux -o -name \*.cp -o -name \*.fn -o -name \*.ky -o -name \*.pg -o -name \*.tp -o -name \*.vr -o -name \*.cps -o -name \*.fns -o -name \*.kys -o -name \*.pgs -o -name \*.tps -o -name \*.vrs -o -name \*.pyc -o -name \*.pyo \) -prune -o  -type f \( -name \*.py \) -exec grep -i -nH -e apt_install \{\} +
./charmhelpers/contrib/hardening/host/checks/pam.py:26:    apt_install,
./charmhelpers/contrib/hardening/host/checks/pam.py:89:            apt_install(pkg)
./charmhelpers/contrib/hardening/host/checks/pam.py:125:        apt_install('libpam-modules')
./charmhelpers/contrib/hardening/ssh/checks/config.py:27:    apt_install,
./charmhelpers/contrib/hardening/ssh/checks/config.py:199:        apt_install(settings['client']['package'])
./charmhelpers/contrib/hardening/ssh/checks/config.py:277:        apt_install(settings['server']['package'])
./charmhelpers/contrib/hardening/templating.py:27:    from charmhelpers.fetch import apt_install
./charmhelpers/contrib/hardening/templating.py:31:        apt_install('python-jinja2', fatal=True)
./charmhelpers/contrib/hardening/templating.py:33:        apt_install('python3-jinja2', fatal=True)
./charmhelpers/contrib/storage/linux/ceph.py:64:    apt_install,
./charmhelpers/contrib/storage/linux/ceph.py:729:    apt_install('ceph-common', fatal=True)
./charmhelpers/contrib/openstack/context.py:27:    apt_install,
./charmhelpers/contrib/openstack/context.py:106:        apt_install('python-psutil', fatal=True)
./charmhelpers/contrib/openstack/context.py:108:        apt_install('python3-psutil', fatal=True)
./charmhelpers/contrib/openstack/context.py:119:        apt_install(required, fatal=True)
./charmhelpers/contrib/openstack/keystone.py:18:from charmhelpers.fetch import apt_install
./charmhelpers/contrib/openstack/keystone.py:121:                apt_install(["python-keystoneclient"], fatal=True)
./charmhelpers/contrib/openstack/keystone.py:123:                apt_install(["python3-keystoneclient"], fatal=True)
./charmhelpers/contrib/openstack/keystone.py:155:                apt_install(["python-keystoneclient"], fatal=True)
./charmhelpers/contrib/openstack/keystone.py:157:                apt_install(["python3-keystoneclient"], fatal=True)
./charmhelpers/contrib/openstack/templating.py:19:from charmhelpers.fetch import apt_install, apt_update
./charmhelpers/contrib/openstack/templating.py:32:        apt_install('python-jinja2', fatal=True)
./charmhelpers/contrib/openstack/templating.py:34:        apt_install('python3-jinja2', fatal=True)
./charmhelpers/contrib/openstack/templating.py:214:                apt_install('python-jinja2')
./charmhelpers/contrib/openstack/templating.py:216:                apt_install('python3-jinja2')
./charmhelpers/contrib/openstack/utils.py:85:    apt_install,
./charmhelpers/contrib/openstack/utils.py:591:        apt_install('ubuntu-cloud-keyring', fatal=True)
./charmhelpers/contrib/database/mysql.py:43:    apt_install,
./charmhelpers/contrib/database/mysql.py:54:        apt_install(filter_installed_packages(['python-mysqldb']), fatal=True)
./charmhelpers/contrib/database/mysql.py:56:        apt_install(filter_installed_packages(['python3-mysqldb']), fatal=True)
./charmhelpers/contrib/network/ovs/__init__.py:20:from charmhelpers.fetch import apt_install
./charmhelpers/contrib/network/ovs/__init__.py:90:            apt_install('python-netifaces', fatal=True)
./charmhelpers/contrib/network/ovs/__init__.py:92:            apt_install('python3-netifaces', fatal=True)
./charmhelpers/contrib/network/ip.py:23:from charmhelpers.fetch import apt_install, apt_update
./charmhelpers/contrib/network/ip.py:42:        apt_install('python-netifaces', fatal=True)
./charmhelpers/contrib/network/ip.py:44:        apt_install('python3-netifaces', fatal=True)
./charmhelpers/contrib/network/ip.py:52:        apt_install('python-netaddr', fatal=True)
./charmhelpers/contrib/network/ip.py:54:        apt_install('python3-netaddr', fatal=True)
./charmhelpers/contrib/network/ip.py:447:            apt_install('python-dnspython', fatal=True)
./charmhelpers/contrib/network/ip.py:449:            apt_install('python3-dnspython', fatal=True)
./charmhelpers/contrib/network/ip.py:498:                apt_install("python-dnspython", fatal=True)
./charmhelpers/contrib/network/ip.py:500:                apt_install("python3-dnspython", fatal=True)
./charmhelpers/contrib/ansible/__init__.py:135:    charmhelpers.fetch.apt_install('ansible')
./charmhelpers/contrib/templating/jinja.py:19:from charmhelpers.fetch import apt_install, apt_update
./charmhelpers/contrib/templating/jinja.py:25:        apt_install(["python3-jinja2"], fatal=True)
./charmhelpers/contrib/templating/jinja.py:27:        apt_install(["python-jinja2"], fatal=True)
./charmhelpers/contrib/python/packages.py:23:from charmhelpers.fetch import apt_install, apt_update
./charmhelpers/contrib/python/packages.py:44:                apt_install('python-pip')
./charmhelpers/contrib/python/packages.py:46:                apt_install('python3-pip')
./charmhelpers/contrib/python/packages.py:144:        apt_install('python-virtualenv')
./charmhelpers/contrib/python/packages.py:146:        apt_install('python3-virtualenv')
./charmhelpers/contrib/mellanox/infiniband.py:23:    apt_install,
./charmhelpers/contrib/mellanox/infiniband.py:36:        apt_install('python-netifaces')
./charmhelpers/contrib/mellanox/infiniband.py:38:        apt_install('python3-netifaces')
./charmhelpers/contrib/mellanox/infiniband.py:88:    apt_install(REQUIRED_PACKAGES, fatal=True)
./charmhelpers/contrib/saltstack/__init__.py:104:    charmhelpers.fetch.apt_install('salt-common')
./charmhelpers/fetch/__init__.py:88:    apt_install = fetch.install
./charmhelpers/fetch/__init__.py:100:    apt_install = fetch.install
./charmhelpers/core/templating.py:43:    installed, calling this will attempt to use charmhelpers.fetch.apt_install
./charmhelpers/core/templating.py:50:            from charmhelpers.fetch import apt_install
./charmhelpers/core/templating.py:57:            apt_install('python-jinja2', fatal=True)
./charmhelpers/core/templating.py:59:            apt_install('python3-jinja2', fatal=True)
./tests/contrib/storage/test_linux_ceph.py:612:    @patch.object(ceph_utils, 'apt_install')
./tests/contrib/openstack/test_os_contexts.py:2106:    @patch.object(context, 'apt_install')
./tests/contrib/openstack/test_os_templating.py:59:        self.addCleanup(patch.object(templating, 'apt_install').start().stop())
./tests/contrib/openstack/test_os_templating.py:69:    @patch.object(templating, 'apt_install')
./tests/contrib/openstack/test_keystone_utils.py:10:    'apt_install',
./tests/contrib/openstack/test_openstack_utils.py:496:    @patch('charmhelpers.contrib.openstack.utils.apt_install')
./tests/contrib/network/test_ip.py:618:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:619:    def test_get_host_ip_with_hostname(self, apt_install):
./tests/contrib/network/test_ip.py:627:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:628:    def test_get_host_ip_with_hostname_no_dns(self, apt_install, socket,
./tests/contrib/network/test_ip.py:640:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:641:    def test_get_host_ip_with_hostname_fallback(self, apt_install, socket,
./tests/contrib/network/test_ip.py:654:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:655:    def test_get_host_ip_with_ip(self, apt_install):
./tests/contrib/network/test_ip.py:661:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:662:    def test_ns_query_trigger_apt_install(self, apt_install):
./tests/contrib/network/test_ip.py:667:                apt_install.assert_called_with('python-dnspython', fatal=True)
./tests/contrib/network/test_ip.py:669:                apt_install.assert_called_with('python3-dnspython', fatal=True)
./tests/contrib/network/test_ip.py:672:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:673:    def test_ns_query_ptr_record(self, apt_install):
./tests/contrib/network/test_ip.py:679:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:680:    def test_ns_query_a_record(self, apt_install):
./tests/contrib/network/test_ip.py:687:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:688:    def test_ns_query_blank_record(self, apt_install):
./tests/contrib/network/test_ip.py:694:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:695:    def test_ns_query_lookup_fail(self, apt_install):
./tests/contrib/network/test_ip.py:701:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:702:    def test_get_hostname_with_ip(self, apt_install):
./tests/contrib/network/test_ip.py:708:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:709:    def test_get_hostname_with_ip_not_fqdn(self, apt_install):
./tests/contrib/network/test_ip.py:715:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:716:    def test_get_hostname_with_hostname(self, apt_install):
./tests/contrib/network/test_ip.py:720:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:721:    def test_get_hostname_with_hostname_trailingdot(self, apt_install):
./tests/contrib/network/test_ip.py:725:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:726:    def test_get_hostname_with_hostname_not_fqdn(self, apt_install):
./tests/contrib/network/test_ip.py:730:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:731:    def test_get_hostname_trigger_apt_install(self, apt_install):
./tests/contrib/network/test_ip.py:737:                apt_install.assert_called_with('python-dnspython', fatal=True)
./tests/contrib/network/test_ip.py:739:                apt_install.assert_called_with('python3-dnspython', fatal=True)
./tests/contrib/network/test_ip.py:745:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:746:    def test_get_hostname_lookup_fail(self, apt_install, ns_query, socket):
./tests/contrib/network/test_ip.py:756:    @patch('charmhelpers.contrib.network.ip.apt_install')
./tests/contrib/network/test_ip.py:758:            self, apt_install, ns_query, socket):
./tests/contrib/network/test_ovs.py:110:    "apt_install",
./tests/contrib/ansible/test_ansible.py:46:        self.mock_fetch.apt_install.assert_called_once_with(
./tests/contrib/ansible/test_ansible.py:54:        self.mock_fetch.apt_install.assert_called_once_with(
./tests/contrib/python/test_packages.py:13:    "apt_install",
./tests/contrib/python/test_packages.py:27:        self.apt_install.return_value = True
./tests/contrib/python/test_packages.py:174:            self.apt_install.assert_called_with('python-virtualenv')
./tests/contrib/python/test_packages.py:176:            self.apt_install.assert_called_with('python3-virtualenv')
./tests/contrib/saltstack/test_saltstates.py:34:        self.mock_charmhelpers_fetch.apt_install.assert_called_once_with(
./tests/contrib/saltstack/test_saltstates.py:42:        self.mock_charmhelpers_fetch.apt_install.assert_called_once_with(
./tests/fetch/test_fetch.py:804:        fetch.apt_install(packages, options)
./tests/fetch/test_fetch.py:821:        fetch.apt_install(packages)
./tests/fetch/test_fetch.py:839:        fetch.apt_install(packages, options)
./tests/fetch/test_fetch.py:857:        fetch.apt_install(packages, options, fatal=True)

Grep finished (matches found) at Sat May 27 22:32:10

Enough proof that default charms will break. Let's see how to fix it.

Python2 fix

Strategy: make a charm Python2 compatible.

This can be broken down to the following steps:

Use python27 (in hooks).
Change python search path in hooks.
Map apt_ function for CentOS in charmhelpers.
Update RelationBase class definition charms.reactive lib to use Python2 syntax.
Update layer-basic.

Python27 in hooks

If you run charm build and search python3 in dist folder, the first offender are hooks:

#!/usr/bin/env python3

change to:

#!/usr/bin/env python

The root cause is actually the hook.template, which is used in a copy-paste fashion to create the list of default hooks if user didn't define one. Remember, the hooks are hardcoded, and certain hooks will always be created!

`sys.path` in hooks

Update Python search path used in all hooks:

# Load modules from $JUJU_CHARM_DIR/lib
import sys
sys.path.append('lib')

change to:

# Load modules from $JUJU_CHARM_DIR/lib
import sys
import os
sys.path.append(os.path.join(os.getcwd(),'lib'))

Btw, don't be fooled by the comment line $JUJU_CHARM_DIR, there isn't one. Otherwise, there is no need to make this change.

Function mapping in `charmhelpers`

Update charmhelpers/fetch/__init__.py to add CentOS function mappings:

if __platform__ == "ubuntu":
    apt_cache = fetch.apt_cache
    apt_install = fetch.install
    apt_update = fetch.update
    apt_upgrade = fetch.upgrade
    apt_purge = fetch.purge
    apt_mark = fetch.apt_mark
    apt_hold = fetch.apt_hold
    apt_unhold = fetch.apt_unhold
    get_upstream_version = fetch.get_upstream_version
elif __platform__ == "centos":
    yum_search = fetch.yum_search

    # ADD: centos mapping
    apt_install = fetch.install
    apt_upgrade = fetch.upgrade
    apt_update = fetch.update
    apt_purge = fetch.purge
    apt_cache = fetch.yum_search

`RelationBase` in `charms.reactive`

Update class RelationBase in charms.reactive/charms/reactive/relations.py:

class RelationBase(object, metaclass=AutoAccessors):
    """
    The base class for all relation implementations.
    """

change to:

class RelationBase(object):
    __metaclass__=AutoAccessors

`layer-basic`

layer-basic is inherited in all charms. We will have a separate analysis on this lib alone. For now, let's take it for granted and work around the issues to make Python2 charms.

Diff file list:

Files layer-basic/bin/layer_option
Only in /home/fengxia/workspace/wss/charms/layer-basic/lib/charms: __init__.py
Files layer-basic/lib/charms/layer/basic.py 
Files layer-basic/lib/charms/layer/execd.py

`sys.path` in `layer_option`

Update layer-basic/bin/layer-optioin. This is the same change made in hooks.

import sys
sys.path.append('lib')

change to:

import sys
import os
sys.path.append(os.path.join(os.getcwd(),'lib'))

Python import path

Touch an empty file layer-basic/lib/charms/__init__.py → make Python2 search path work.

`basic.py`

Changes to this file look intimidating (showing diff -r old new). However, the theme is quite straightforward:

Install python2 modules, eg python-setuptools, as prerequisite to prepare the environment (bug #97).
The correct binary path for your pip.
Use platform.linux_distribution()[0] to determine host platform.
apt uses --assume-yes, where yum uses --assumeyes.

There are mixed apt_install (bug #98) using the mapped function and direct check_call shell calls. Moving forward, we should consolidate all package functions to mapped version.

6a7
> import platform
51,56c52,77
<         apt_install([
<             'python3-pip',
<             'python3-setuptools',
<             'python3-yaml',
<             'python3-dev',
<         ])
---
>         me = platform.linux_distribution()[0]
>         if 'ubuntu' in me.lower():
>             apt_install([
>                 'python3-pip',
>                 'python3-setuptools',
>                 'python3-yaml',
>                 'python3-dev',
>             ])
>         elif 'cent' in me.lower():
>             # if using python3
>             #apt_install([
>             #    'redhat-lsb-core',
>             #    'python34-setuptools',
>             #    'python34-pip',
>             #    'python34-yaml',
>             #    'python34-devel',
>             #])
>             apt_install([
>                 'epel-release', # must
>                 'redhat-lsb-core',
>                 'python-setuptools',
>                 'python-pip',
>                 'python-yaml',
>                 'python-devel',
>             ])
> 
64c85,88
<                 series = lsb_release()['DISTRIB_CODENAME']
---
>                 try:
>                     series = lsb_release()['DISTRIB_CODENAME']
>                 except:
>                     series = 'centos7'
66a91
>                     pip = vpip
68c93,96
<                     apt_install(['virtualenv'])
---
>                     # pip = 'pip3' # if using python3
>                     pip = 'pip'
>                     check_call([pip, 'install', '-U', '--no-index', '-f', 'wheelhouse','pip'])
>                     check_call([pip, 'install', 'virtualenv'])
74d101
<             pip = vpip
76c103,104
<             pip = 'pip3'
---
>             # pip = 'pip3' # if using python3
>             pip = vpip
83,84c111,114
<         check_call([pip, 'install', '-U', '--no-index', '-f', 'wheelhouse',
<                     'pip'])
---
>     
>         # TODO: feng
>         pip = 'pip' # this is a hack to use Python2
>         check_call([pip, 'install', '-U', '--no-index', '-f', 'wheelhouse','pip'])
86,87c116
<         check_call([pip, 'install', '-U', '--no-index', '-f', 'wheelhouse'] +
<                    glob('wheelhouse/*'))
---
>         check_call([pip, 'install', '-U', '--no-index', '-f', 'wheelhouse'] + glob('wheelhouse/*'))
113c142,143
<         sys.path.append('lib')
---
>         import os
>         sys.path.append(os.path.join(os.getcwd(),'lib'))
157c187,190
<     cmd = ['apt-get',
---
>     me = platform.linux_distribution()[0]
>     if 'ubuntu' in me.lower():
>         my_cmd = 'apt-get'
>         cmd = [my_cmd,
160a194,199
>     elif 'cent' in me.lower():
>         my_cmd = 'yum'
>         cmd = [my_cmd,
>            '--assumeyes',
>            'install']
>

`execd.py`

A formatting error?

17a18
> from __future__ import print_function
114,115c115
<             print("ERROR ({}) running {}".format(e.returncode, e.cmd),
<                   file=stderr)
---
>             print("ERROR ({}) running {}".format(e.returncode, e.cmd),file=stderr)

How to build

git clone http://hpcgitlab.labs.lenovo.com/WSS/wss.git.
Copy (or symlink) wss/hack/layer-basic to LAYER_PATH.
charm build your charm as usual.
Copy wss/hack/charmhelpers....tar.gz and charms.reactive....tar.gz to dist/trusty(or centos)/yourcharm/wheelhouse.
Copy wss/hack/hooks to dist/.../hooks. However, if you have customized hooks, you need to make modifications manually.

Have fun with CentOS.

— by Feng Xia

Juju charm Python2

CentOS challenge

Python2 fix

Python27 in hooks

`sys.path` in hooks

Function mapping in `charmhelpers`

`RelationBase` in `charms.reactive`

`layer-basic`

`sys.path` in `layer_option`

Python import path

`basic.py`

`execd.py`

How to build

Related:

Juju GUI nginx proxy

Juju local LXD

Charm Ansible integration

Juju charm Python2

CentOS challenge

Python2 fix

Python27 in hooks

sys.path in hooks

Function mapping in charmhelpers

RelationBase in charms.reactive

layer-basic

sys.path in layer_option

Python import path

basic.py

execd.py

How to build

Related:

Juju GUI nginx proxy

Juju local LXD

Charm Ansible integration

`sys.path` in hooks

Function mapping in `charmhelpers`

`RelationBase` in `charms.reactive`

`layer-basic`

`sys.path` in `layer_option`

`basic.py`

`execd.py`