# Advanced Charm Development There are a handful of tips that make development and testing of charms a less time-consuming effort. ## Faster Deployments When a charm is deployed, there are several time-consuming steps that are executed by default. 1. Launch an LXD container - download or update the cloud image for the series of charm being deployed 2. Run *apt-get update && apt-get upgrade* 3. Provision the machine with the Juju machine agent 4. Install charm (execute hooks, i.e., install, start) ### Build a custom cloud image Caveat: This is intended only for use in a development environment, to provide faster iteration between deploying VNFs and charms. The script below can be taken as-is We start with the base cloud image that LXD downloads from its [image server](https://us.images.linuxcontainers.org/), update it's installed software, and install the packages required by the reactive charm framework. 1. Launch a container using the latest cloud image 2. Run *apt-get update* and *apt-get upgrade* 3. Install extra packages needed by the reactive framework and your charm(s) 4. Publish the container as an image, under the alias *juju/$series/amd64* **Note**: It's highly recommended to place this script into a nightly or weekly cron, so that you have relatively current updates. ``` #!/bin/bash # # This script will create trusty, xenial and/or bionic lxd images that will be used by the # lxd provider in juju 2.1+ It is for use with the lxd provider for local # development and preinstalls a common set of packages. # # This is important, as between them, basenode and layer-basic install ~111 # packages, before we even get to any packages installed by your charm. # # It also installs some helpful development tools, and pre-downloads some # commonly used packages. # # This dramatically speeds up the install hooks for lxd deploys. On my slow # laptop, average install hook time went from ~7min down to ~1 minute. set -eux # The basic charm layer also installs all the things. 47 packages. LAYER_BASIC="gcc build-essential python3-pip python3-setuptools python3-yaml" # the basic layer also installs virtualenv, but the name changed in xenial. TRUSTY_PACKAGES="python-virtualenv" XENIAL_PACKAGES="virtualenv" BIONIC_PACKAGES="virtualenv" # Predownload common packages used by your charms in development DOWNLOAD_PACKAGES= PACKAGES="$LAYER_BASIC $DOWNLOAD_PACKAGES" function cache() { series=$1 container=juju-${series}-base alias=juju/$series/amd64 lxc delete $container -f || true lxc launch ubuntu:$series $container sleep 15 # wait for network lxc exec $container -- apt update -y lxc exec $container -- apt upgrade -y lxc exec $container -- apt install -y $PACKAGES $2 lxc stop $container lxc image delete $alias || true lxc publish $container --alias $alias description="$series juju dev image ($(date +%Y%m%d))" lxc delete $container -f || true } # Uncomment the series you need pre-cached. By default, this will only # cache the most recent series -- currently bionic. # cache trusty "$TRUSTY_PACKAGES" cache xenial "$XENIAL_PACKAGES" # cache bionic "$BIONIC_PACKAGES" ``` ### Disable OS upgrades Prevent Juju from running *apt-get update && apt-get upgrade* when starting a machine ``` juju model-config enable-os-refresh-update=false enable-os-upgrade=false ``` Please note that any 'juju model-config' command needs to run right aftert you have switched to the juju model of your Network Service, in order to work. ### Using a custom Apt repository You can configure Juju to use a local or regional Apt repository: ``` juju model-config apt-mirror=http://archive.ubuntu.com/ubuntu/ ``` Please note that any 'juju model-config' command needs to run right aftert you have switched to the juju model of your Network Service, in order to work. ### Using a proxy server Due to policy or network bandwidth, you may want to use a proxy server. Juju supports several types of proxy server, including: - http-proxy - https-proxy - apt-http-proxy - apt-https-proxy ``` juju model-config apt-http-proxy=http://squid.internal:3128 apt-https-proxy=https://squid.internal:3128 ``` You can find a complete list of [model configuration](https://docs.jujucharms.com/2.4/en/models-config) keys in the [Juju Documentation](https://docs.jujucharms.com/2.4/en/). ## Debugging [Debugging Charm Hooks](https://docs.jujucharms.com/2.4/en/developer-debugging) is a good place to start to familiarize yourself with the process and available ways of debugging a charm. ### Debug Logs It's useful to watch the debug-logs while deploying a charm, to confirm what hooks are being run and to catch any exceptions that are raised. By default, it will tail the log for all charms: ``` $ juju debug-log unit-charmnative-vnf-a-5: 18:12:11 INFO unit.charmnative-vnf-a/5.juju-log Reactive main running for hook start unit-charmnative-vnf-a-5: 18:12:13 INFO unit.charmnative-vnf-a/5.juju-log Reactive main running for hook test unit-charmnative-vnf-a-5: 18:12:13 INFO unit.charmnative-vnf-a/5.juju-log Invoking reactive handler: reactive/native-ci.py:21:test unit-charmnative-vnf-a-5: 18:12:13 INFO unit.charmnative-vnf-a/5.juju-log Reactive main running for hook test unit-charmnative-vnf-a-5: 18:12:13 INFO unit.charmnative-vnf-a/5.juju-log Invoking reactive handler: reactive/native-ci.py:21:test unit-charmnative-vnf-a-5: 18:12:14 INFO unit.charmnative-vnf-a/5.juju-log Reactive main running for hook testint unit-charmnative-vnf-a-5: 18:12:14 INFO unit.charmnative-vnf-a/5.juju-log Invoking reactive handler: reactive/native-ci.py:33:testint unit-charmnative-vnf-a-5: 18:13:17 WARNING juju.worker.uniter.operation we should run a leader-deposed hook here, but we can't yet unit-charmnative-vnf-a-5: 18:13:18 INFO unit.charmnative-vnf-a/5.juju-log Reactive main running for hook leader-settings-changed unit-charmnative-vnf-a-5: 18:13:18 INFO unit.charmnative-vnf-a/5.juju-log Reactive main running for hook stop ``` ### Interactive Debugging One of the more useful, advanced tools we have is the *juju debug-hook* command, which lets us interact with the charm in a tmux session inside the container. This allows us to edit code and re-run it, use pdb, and inspect configuration and state. Please refer to the [Developer Debugging](https://docs.jujucharms.com/2.4/en/developer-debugging) docs for more information about how to do this.