Hello, Juju! Charm

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.

Quickstart

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       Running

With 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.

Using PostgreSQL

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       peer

The application will behave exactly as before, but now the request store will be stored in the PostgreSQL database

Development Setup

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

Build and Deploy Locally

# 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

Testing

# 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_tests

Get Help & Community

If you get stuck deploying this charm, or would like help with charming generally, come and join the charming community!

More Information/Related

Below are some links related to this demo charm:

juju/hello-juju-charm