This charm is a demonstration machine charm written with the Charmed Operator Framework.
It deploys a simple Python Flask web application. The application itself is simple, and counts the number of times the root URL has been requested and stores the count in a database. With no database relation defined, this information is stored in a SQLite database.
This charm also supports a relation to the PostgreSQL charm. When this relation is established the Flask application is automatically configured to use the PostgreSQL database to store its count.
Assuming you already have Juju installed and bootstrapped on a cloud, such as LXD:
# Create a model
$ juju add-model dev
# Deploy the charm
$ juju deploy hello-juju
# Wait for the deployment to complete
$ juju status
Model Controller Cloud/Region Version SLA Timestamp
dev lxd localhost/localhost 2.9.1 unsupported 14:46:51+01:00
App Version Status Scale Charm Store Channel Rev OS Message
hello-juju active 1 hello-juju local 0 ubuntu
Unit Workload Agent Machine Public address Ports Message
hello-juju/0* active idle 0 10.14.25.117 80/tcp
Machine State DNS Inst id Series AZ Message
0 started 10.14.25.117 juju-9f46aa-0 focal RunningWith the example above, the page would be available at http://10.14.25.117 in a browser. Once visited/refreshed a couple of times, the URL http://10.14.25.117/greetings would display a count of how many times the page has been requested.
To use PostgreSQL as the backing database, deploy the charm, then deploy PostgreSQL
and relate the two applications, specifying the db interface.
Assuming you already have the hello-juju charm deployed, you can start using
PostgreSQL like so:
# Deploy PostgreSQL
$ juju deploy postgresql
# Relate the two applications
$ juju relate hello-juju postgresql:db
# Check the status:
$ juju status --relations
Model Controller Cloud/Region Version SLA Timestamp
dev lxd localhost/localhost 2.9.1 unsupported 14:55:47+01:00
App Version Status Scale Charm Store Channel Rev OS Message
hello-juju active 1 hello-juju local 1 ubuntu
postgresql 12.6 active 1 postgresql charmhub stable 233 ubuntu Live master (12.6)
Unit Workload Agent Machine Public address Ports Message
hello-juju/0* active idle 2 10.14.25.117 80/tcp
postgresql/0* active idle 1 10.14.25.157 5432/tcp Live master (12.6)
Machine State DNS Inst id Series AZ Message
1 started 10.14.25.157 juju-9f46aa-1 focal Running
2 started 10.14.25.117 juju-9f46aa-2 focal Running
Relation provider Requirer Interface Type Message
postgresql:coordinator postgresql:coordinator coordinator peer
postgresql:db hello-juju:db pgsql regular
postgresql:replication postgresql:replication pgpeer peerThe application will behave exactly as before, but now the request store will be stored in the PostgreSQL database
To set up a local test environment with LXD:
# Install LXD
$ sudo snap install --classic lxd
# Configure LXD with defaults
$ sudo lxd init --auto
# (Optional) Add your user to the LXD group
$ newgrp lxd
$ sudo adduser $(whoami) lxd
# Install Charmcraft
$ sudo snap install charmcraft
# Install juju
$ sudo snap install --classic juju
# Bootstrap the Juju controller on lxd
$ juju bootstrap localhost lxd
# Add a new model to Juju
$ juju add-model dev# Clone the charm code
$ git clone https://github.com/juju/hello-juju && cd hello-juju
# Build the charm package
$ charmcraft pack
# Deploy!
$ juju deploy ./hello-juju.charm
# Wait for the deployment to complete
$ watch -n1 --color juju status --color# Clone the charm code
$ git clone https://github.com/juju/hello-juju && cd hello-juju
# Install python3-virtualenv
$ sudo apt update && sudo apt install -y python3-virtualenv
# Create a virtualenv for the charm code
$ virtualenv venv
# Activate the venv
$ source ./venv/bin/activate
# Install dependencies
$ pip install -r requirements-dev.txt
# Run the tests
$ ./run_testsIf you get stuck deploying this charm, or would like help with charming generally, come and join the charming community!
Below are some links related to this demo charm: