CloudFront — alert on rising 5xx error rate

#!/usr/bin/env bash
# 5xx-error-rate over the last 5 minutes.
DIST="${CF_DIST:?must be set}"
THRESHOLD_PCT="${THRESHOLD_PCT:-2}"

NOW=$(date -u -d '5 min ago' +%FT%TZ)
END=$(date -u +%FT%TZ)

PCT=$(aws cloudwatch get-metric-statistics \
  --namespace AWS/CloudFront --metric-name 5xxErrorRate \
  --dimensions Name=DistributionId,Value="$DIST" Name=Region,Value=Global \
  --start-time "$NOW" --end-time "$END" \
  --period 60 --statistics Average \
  --query 'Datapoints[-1].Average' --output text 2>/dev/null)

[ -z "$PCT" ] || [ "$PCT" = "None" ] && { echo "no-data"; exit 0; }
PCT_INT=$(printf "%.0f" "$PCT")
[ "$PCT_INT" -ge "$THRESHOLD_PCT" ] && echo "high ${PCT_INT}%" || echo "ok ${PCT_INT}%"