Canary: Post-Deploy monitoring

Watch a live application after deployment. Alert on errors and regressions. Compare against a pre-deploy baseline.

Two modes:

--baseline: capture the current state BEFORE deploying
(default): monitor AFTER deploying and compare against baseline

Instructions

Phase 1: Setup

Parse the user's arguments and detect the deployment context.

# Detect current branch and recent deploy commit
git branch --show-current
git log --oneline -5

# Auto-detect platform from config files
[ -f fly.toml ]         && echo "PLATFORM: fly"
[ -f render.yaml ]      && echo "PLATFORM: render"
[ -f vercel.json ]      && echo "PLATFORM: vercel"
[ -f netlify.toml ]     && echo "PLATFORM: netlify"
[ -f Procfile ]         && echo "PLATFORM: heroku"
[ -f railway.toml ]     && echo "PLATFORM: railway"

# Check for health endpoint
curl -sf "${URL}/health" -w "\n%{http_code}" 2>/dev/null | tail -1
curl -sf "${URL}/api/health" -w "\n%{http_code}" 2>/dev/null | tail -1

Create the working directory:

mkdir -p .canary/baselines .canary/reports .canary/screenshots

Phase 2: Baseline Capture (`--baseline` mode)

Run this BEFORE deploying to capture the current healthy state.

For each page to monitor, record:

HTTP status: is the page returning 200?
Response time: how long does it take to load?
Content snapshot: key text content to detect blank pages later

# For each page URL
for PAGE_PATH in "/" "/dashboard" "/settings" "/api/health"; do
  SLUG=$(echo "$PAGE_PATH" | tr '/' '_' | tr -d '?&=')
  RESULT=$(curl -sf -o /dev/null -w "%{http_code}|%{time_total}" "${BASE_URL}${PAGE_PATH}" 2>/dev/null)
  STATUS=$(echo "$RESULT" | cut -d'|' -f1)
  TIME_MS=$(echo "$RESULT" | awk -F'|' '{printf "%.0f", $2 * 1000}')
  echo "  ${PAGE_PATH}: HTTP ${STATUS}, ${TIME_MS}ms"
done

Save baseline to .canary/baselines/baseline.json:

{
  "url": "<base-url>",
  "timestamp": "<ISO-8601>",
  "branch": "<branch-name>",
  "commit": "<git-SHA>",
  "pages": {
    "/": { "status": 200, "time_ms": 450 },
    "/dashboard": { "status": 200, "time_ms": 680 },
    "/api/health": { "status": 200, "time_ms": 45 }
  }
}

Then STOP and tell the user: "Baseline captured. Deploy your changes, then run /canary <url> to monitor."

Phase 3: Page discovery

If no pages were specified, auto-discover pages to monitor.

From the application:

# Check sitemap if available
curl -sf "${URL}/sitemap.xml" 2>/dev/null | grep -oP '(?<=<loc>)[^<]+' | head -10

# Check robots.txt for known paths
curl -sf "${URL}/robots.txt" 2>/dev/null | grep -i "allow\|disallow" | head -10

# Common paths to always check
echo "Always check: / /login /dashboard /settings /api/health"

Default pages to monitor if nothing found: /, and the homepage only.

Phase 4: Monitoring loop

Monitor for the specified duration (default: 10 minutes). Run a check every 60 seconds.

Each check cycle:

TIMESTAMP=$(date -u +%Y-%m-%dT%H:%M:%SZ)
CHECK_NUM=$((CHECK_NUM + 1))

for PAGE_PATH in "${PAGES[@]}"; do
  # Check HTTP status and response time
  RESULT=$(curl -sf -o /dev/null -w "%{http_code}|%{time_total}" \
    --max-time 10 "${BASE_URL}${PAGE_PATH}" 2>/dev/null || echo "0|0")
  STATUS=$(echo "$RESULT" | cut -d'|' -f1)
  TIME_MS=$(echo "$RESULT" | awk -F'|' '{printf "%.0f", $2 * 1000}')

  # Compare against baseline
  BASELINE_STATUS=$(jq -r ".pages[\"${PAGE_PATH}\"].status // 200" .canary/baselines/baseline.json 2>/dev/null)
  BASELINE_TIME=$(jq -r ".pages[\"${PAGE_PATH}\"].time_ms // 1000" .canary/baselines/baseline.json 2>/dev/null)

  echo "  [Check #${CHECK_NUM}] ${PAGE_PATH}: HTTP ${STATUS} (${TIME_MS}ms)"
done

Alert levels:

Level	Condition	Trigger
CRITICAL	Page load failure	HTTP status is not 2xx, curl timeout, DNS failure
HIGH	New errors	Error rate increased vs baseline (console errors, 5xx responses)
MEDIUM	Performance regression	Response time exceeds 2x baseline
LOW	New broken links	Previously-working routes now return 404

Key principles:

Alert on changes, not absolutes. A page with 3 errors in baseline is fine if still 3. One NEW error is an alert.
Transient tolerance. Only alert on patterns persisting across 2+ consecutive checks. A single network blip is not an alert.

When a CRITICAL or HIGH alert fires (2 consecutive checks):

CANARY ALERT
=====================================
Time:     [check #N at Xs elapsed]
Page:     [URL]
Level:    [CRITICAL / HIGH / MEDIUM / LOW]
Finding:  [what changed, be specific]
Baseline: [baseline value]
Current:  [current value]
=====================================
Options:
  A) Investigate now: stop monitoring, focus on this issue
  B) Continue monitoring: wait for next check to confirm
  C) Rollback: revert the deploy
  D) Dismiss: known issue, continue monitoring

Phase 5: Health report

After monitoring completes (or user stops), produce a summary.

CANARY REPORT: [url]
=========================================
Duration:    [X minutes]
Checks:      [N total per page]
Pages:       [N pages monitored]
Commit:      [deployed SHA]
Status:      [HEALTHY / DEGRADED / BROKEN]

Per-Page Results:
-----------------------------------------
  Page           Status      Avg Time   Alerts
  /              HEALTHY     450ms      0
  /dashboard     DEGRADED    1100ms     1 medium (was 450ms)
  /settings      HEALTHY     380ms      0
  /api/health    HEALTHY     45ms       0

Alerts Fired: [N] (X critical, Y high, Z medium, W low)

VERDICT: [DEPLOY HEALTHY / DEPLOY HAS ISSUES (see alerts above)]
=========================================

Save report to .canary/reports/<date>-canary.md.

Phase 6: Baseline update

If the deploy is healthy and the user wants to update the baseline:

cp .canary/reports/latest-snapshot.json .canary/baselines/baseline.json
echo "Baseline updated to commit $(git rev-parse --short HEAD)"

Output format

See Phase 5 above for the full CANARY REPORT template.

Inline alert format (during monitoring):

[08:42:15] Check #3: /dashboard: ALERT HIGH, response time 1250ms (baseline: 420ms)
[08:43:15] Check #4: /dashboard: ALERT HIGH, response time 1180ms (baseline: 420ms)
-> Consistent across 2 checks. Firing alert.

Usage

/canary https://app.example.com                # Monitor homepage for 10 min
/canary https://app.example.com --baseline     # Capture baseline before deploying
/canary https://app.example.com --duration 5m  # Monitor for 5 minutes
/canary https://app.example.com --quick        # Single-pass health check (no loop)
/canary https://app.example.com --pages /,/dashboard,/api/health

Tips

Always capture a baseline before deploying to production: run /canary <url> --baseline
Start monitoring immediately after deploy; the first 5 minutes catch 90% of regressions
CRITICAL alerts require immediate investigation; don't wait for the monitoring to finish
MEDIUM alerts (performance) may be cache warming; give it 2-3 more checks before acting
Keep .canary/baselines/ in git so any team member can run canary against the same baseline

Related commands

/ship: pre-deploy checklist (run before deploying)
/land-and-deploy: full merge-to-verify pipeline (runs canary automatically)
/qa: interactive QA testing before shipping

$ARGUMENTS

canary