feat: set up basic charm functionality

[florentianayuwono]

Applicable spec: ISD249 - Aproxy Subordinate Charm

Overview

Introduces the implementation of the Aproxy Charm, a subordinate charm designed to manage the aproxy snap. The charm configures and applies nftables rules to intercept outbound HTTP/HTTPS traffic and forward it through the aproxy service. It includes event handlers for lifecycle events (install, start, config_changed, and stop) and ensures proper configuration and cleanup of the aproxy service.

Rationale

To provide transparent proxying capabilities for applications. It ensures that outbound traffic is intercepted and routed through a proxy, enabling centralized traffic management and monitoring.

Juju Events Changes

Added Observers:

• on.install: Handles the installation of the aproxy snap.
• on.start: Configures nftables rules and starts the interception service.
• on.config_changed: Reconfigures the aproxy snap and updates nftables rules when charm configuration changes.
• on.stop: Cleans up nftables rules and removes the aproxy snap during charm removal.

Module Changes

Service Module:

• Introduced _on_install, _on_start, _on_config_changed, and _on_stop methods to handle Juju lifecycle events.
• Added helper methods to encapsulate logic for configuring the aproxy snap and managing nftables rules.
• Implemented logging for better traceability of charm operations.

Observer Module:
Observers for Juju events were added to manage the charm's lifecycle.

Library Changes

No external charm libraries were introduced or modified in this implementation. The charm relies on the ops framework and standard Python libraries subprocess, socket, logging to implement its functionality.

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation for charmhub is updated
• The PR is tagged with appropriate label (urgent, trivial, senior-review-required, documentation)
• The docs/changelog.md is updated with user-relevant changes.

Full documentation will be done in a separate PR.

[gregory-schiano]

Good progress, still some small fixes to do

[gregory-schiano]

Last round of comment I think 👍

[gregory-schiano]

LGTM