Skip to content

Lab — Python Slack Notification Bot

Lab Overview

Purpose: Post structured operational alerts to Slack Incoming Webhooks with dry-run safety.

Scenario: Cert monitor and health checks need a shared notifier. Tokens must never be committed.

Expected outcome: CLI builds a Slack payload; --dry-run (default) prints JSON; --send posts only if SLACK_WEBHOOK_URL is set.

This is a lab, not a tutorial

Apply REST APIs — requests, auth, and resilience and Configuration Management and Secrets.

Business Scenario

On-call misses email. Slack #ops-alerts is the team inbox — but pasting secrets into scripts caused an incident.

Learning Objectives

  • Build Block Kit or simple text payloads
  • Default dry-run; explicit --send
  • Read webhook from env only
  • Timeouts on HTTP POST

Prerequisites

Knowledge

Software

httpx/requests. Optional real webhook. Estimated cost: £0.

Environment

mkdir -p ~/rebash-lab-python-slack/out
cd ~/rebash-lab-python-slack
python3 -m venv .venv && source .venv/bin/activate
pip install 'httpx>=0.27,<1'

Initial State

No webhook required. Optionally export a test webhook for live send.

Task

Create slack_notify.py:

python slack_notify.py --title "Disk warning" --text "/ at 92%" --severity warning
# default dry-run writes out/payload.json
python slack_notify.py --title "Disk warning" --text "/ at 92%" --send  # needs SLACK_WEBHOOK_URL

Refuse --send without env var (exit 2). Redact webhook in logs (show only last 4 chars if you must log).

Validation

python slack_notify.py --title "Test" --text "hello"
test -f out/payload.json
SLACK_WEBHOOK_URL= python slack_notify.py --title t --text x --send; echo $?  # 2
  • Dry-run writes payload without network
  • --send without URL exits 2
  • HTTP client uses a timeout

Troubleshooting

Symptom Fix
403 from Slack Webhook revoked — rotate; stay on dry-run for the lab
Leaked URL in git Use env; add secret scanning (next labs)

Cleanup

deactivate 2>/dev/null || true
rm -rf ~/rebash-lab-python-slack
unset SLACK_WEBHOOK_URL

Production Discussion

Prefer Slack apps with granular scopes over immortal webhooks where possible; rate-limit noisy alerts; route by severity.