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Best practices for contributing to Tengu

Always use the reactive framework and layers when creating a new Charm. Create a separate repository for each layer and bundle. Create a submodule in /bundles pointing to the bundle repo and create a submodule in /charms/layers pointing to the layer repo. Build the charm to /charms/builds and commit the built charm to this repo.

General

Be lazy

Use the charmhelpers library, use existing layers, use existing python libraries.

Be nice to upstream

When you patch existing code, submit the patches upstream so we can throw away our fork when the patches are merged. Every fork you avoid is time we save.

Let the users be lazy

Less config options is better. Remove unimportant config options such as the installation directory. If the Charm can find out what the best option is at runtime, do that.

Say why you do something

Don't bother writing comments about what you're doing. We can all read the code.

Did you just spend the last 4 hours finding the source of a strange intermittent bug? Write a small comment next to the fix to say why that line is critical because if you don't, you'll forget and remove the line in 5 months.

Charming

Change config non-destructively (avoid using templates)

Instead of using templates that completely overwrite existing config files, change them inline. This has a few advantages:

  1. Multiple handlers, layers and users can change a config file. As long as they don't change the same values, this won't be a problem. Some users want to tweak config files that are managed by a Charm manually. This isn't possible if you use templates.
  2. It's more robust. We don't have to update the template when a new version of the application has different default config values.

A handy function for non-destructive editing of config files is the re_edit_in_place function of jujubigdata utils

More rules

  • NO PEP8 ERRORS!!! The pycodestyle linter checks these
  • No Linter errors and no charm proof errors.
  • Always use the check_.. subprocess functions. If error exit code doesn't matter, catch the exception.
  • Don't use shell=True for subprocess commands.
  • Use upstart on trusty and systemd on xenial to start and stop services.
  • use format instead of % for formatting strings. Source

Setting up your dev environment

Install Atom and dependencies

Atom is a good open-source text editor that can be turned into a fully fledged Charming IDE. Following are instructions on how to do that on Ubuntu.

Install Atom

sudo add-apt-repository ppa:webupd8team/atom
sudo apt-get update
sudo apt-get install atom

Install the python package manager and the python packages we need.

# python package manager and dependencies
sudo apt install python-pip python3-pip python-setuptools python3-setuptools\
                 charm-tools juju-deployer

# Dependencies of Charms so linter can check them
sudo pip3 install charms.reactive netifaces amulet click Flask charmhelpers crontab

# Properly display jinja2 templates
apm install atom-jinja2

Show active Juju model in bash prompt

This one is very handy, it show the active Juju model and controller in the bash prompt. (Thanks James Beedy!)

[sojobo:mesebrec/merlijntest] merlijn@travers:~$

Instructions to setup:

cd ~
wget https://gist.githubusercontent.com/jamesbeedy/a5816a6ecd9f64e4bb96c8ba4a153ade/raw/14f255db3172519504e52d8a33ec81e995e8ef66/.juju_context.py
chmod u+x .juju_context.py

And add the following code at the end of .bashrc.

function show_juju_env {
  local currentEnv
  currentEnv=`~/.juju_context.py`
  printf "%s" "$currentEnv"
}

export PS1="[\[\e[38;5;70m\]\$(show_juju_env)\[\e[0m\]] ${PS1}";

Setup Python 2 and Python 3 linting

Pyton linting (code checking) for both python 2 and python 3. We need both pylint and pycodestyle (formerly pep8).

  • Pep8 is the official python style guide. The pycodestyle linter checks this. We should adhere to this without question. pep8 linting is also checked by default by bundletester so we need to be compatible with this.
  • Pylint is incredibly awesome and helps you write good, clean code. However, it can be a bit pedantic at times. You can disable specific warnings by writing #pylint: disable=<code> either at the top of your file or at the line you want to ignore.

Install linting packages.

sudo pip2 install pylint
sudo pip3 install pylint
sudo apt install pycodestyle
apm install linter linter-pylint python-indent linter-pycodestyle

We also want pylint to search the charm's lib directory for python dependencies. Add the following string to the pylint path in the config of the linter-pylint Atom package: %f/../lib.

Setup automatic detection of python2/python3.

mkdir ~/bin

nano ~/bin/pylint and add:

#!/bin/bash
if [[ $(head -n 1 "${@: -1}") == *python3* || $(head -n 1 "${@: -1}" | head -n 1) != *python* ]]
then
  pylint3 --extension-pkg-whitelist=lxml,netifaces "$@"
else
  pylint2 --extension-pkg-whitelist=lxml,netifaces "$@"
fi

nano ~/bin/pylint2 and add:

#!/usr/bin/python2
# EASY-INSTALL-ENTRY-SCRIPT: 'pylint','console_scripts','pylint'
__requires__ = 'pylint'
import sys
from pkg_resources import load_entry_point

if __name__ == '__main__':
    sys.exit(
        load_entry_point('pylint', 'console_scripts', 'pylint')()
    )

nano ~/bin/pylint3 and add:

#!/usr/bin/python3
# EASY-INSTALL-ENTRY-SCRIPT: 'pylint','console_scripts','pylint'
__requires__ = 'pylint'
import sys
from pkg_resources import load_entry_point

if __name__ == '__main__':
    sys.exit(
        load_entry_point('pylint', 'console_scripts', 'pylint')()
    )

and finally: chmod u+x ~/bin/pylint ~/bin/pylint2 ~/bin/pylint3. Log out and log back in to save the changes.

Pylint is a bit to pedantic for us. The following config file tells pylint to ignore some warnings. nano ~/.pylintrc and add the following.

[MASTER]

# Use multiple processes to speed up Pylint.
jobs=2

# Allow loading of arbitrary C extensions. Extensions are imported into the
# active Python interpreter and may run arbitrary code.
unsafe-load-any-extension=no

# A comma-separated list of package or module names from where C extensions may
# be loaded. Extensions are loading into the active Python interpreter and may
# run arbitrary code
extension-pkg-whitelist=lxml,netifaces,pygments


[MESSAGES CONTROL]

# Enable the message, report, category or checker with the given id(s). You can
# either give multiple identifier separated by comma (,) or put this option
# multiple time (only on the command line, not in the configuration file where
# it should appear only once). See also the "--disable" option for examples.
#enable=

max-line-length=99

# Disable the message, report, category or checker with the given id(s). You
# can either give multiple identifiers separated by comma (,) or put this
# option multiple times (only on the command line, not in the configuration
# file where it should appear only once).You can also use "--disable=all" to
# disable everything first and then reenable specific checks. For example, if
# you want to run only the similarities checker, you can use "--disable=all
# --enable=similarities". If you want to run only the classes checker, but have
# no Warning level messages displayed, use"--disable=all --enable=classes
# --disable=W"
disable=c0103,c0111,w1202,r0902,r0903,r0904,r0914,c0325,r0201,w0603,import-star-module-level,old-octal-literal,oct-method,print-statement,unpacking-in-except,parameter-unpacking,backtick,old-raise-syntax,old-ne-operator,long-suffix,dict-view-method,dict-iter-method,metaclass-assignment,next-method-called,raising-string,indexing-exception,raw_input-builtin,long-builtin,file-builtin,execfile-builtin,coerce-builtin,cmp-builtin,buffer-builtin,basestring-builtin,apply-builtin,filter-builtin-not-iterating,using-cmp-argument,useless-suppression,range-builtin-not-iterating,suppressed-message,no-absolute-import,old-division,cmp-method,reload-builtin,zip-builtin-not-iterating,intern-builtin,unichr-builtin,reduce-builtin,standarderror-builtin,unicode-builtin,xrange-builtin,coerce-method,delslice-method,getslice-method,setslice-method,input-builtin,round-builtin,hex-method,nonzero-method,map-builtin-not-iterating

Handy commands and tips

When running juju debug-hooks, you enter a tmux session. The default tmux bindings on Ubuntu are a bit strange. ctrl-a is the default command. To enable sane mouse scrolling set set-window-option -g mode-mouse on in ~/.tmux.conf of the server.

Debug reactive framework

charms.reactive -p get_states

pull PR from github

git pull origin pull/$PR_NUM/head

add submodule as directory

git submodule add <git@github ...> <dirname>

prettyprint json output

| python -m json.tool

grep and get text around match

cat log | grep -A10 <searchterm> # Next 10 lines
cat log | grep -B10 <searchterm> # Previous 10 lines

Debug IP traffic:

iptables -t mangle -I PREROUTING -p icmp --icmp-type 8 -j LOG --log-prefix "ICMP ON MANGLE: "

Mongo

show dbs
use db demo
show collections
coll = db['imec']
coll.find().skip(coll.count() - 20)
coll.find({"subscriptionId": { $exists : true }}).limit(1).sort({$natural:-1})
ObjectId("5714784653628548824c18de").getTimestamp()

Analyse disk space

# Show all folders from `/var` that contain more than a gig of data
sudo du -h /var | grep '[0-9\.]\+G'

# Show the ZFS pools (the disks of the container are part of the zfs pools)
zpool list

# Change the disk quota of a container
lxc config device set juju-f88e04-1-lxd-9 root size 80GB

reconnect to screen

    screen -r

Get DNS name of MAAS server

IPMI_IP=10.2.17.83
dig -x $IPMI_IP  @ns.wall1.ilabt.iminds.be