AWS Transit Gateway Packet Drop Count Sentinel

id: aws-transit-gateway-packet-drop-sentinel
namespace: company.netops

inputs:
  - id: aws_region
    type: STRING
    defaults: us-east-1
    description: AWS region where the Transit Gateway is deployed.
  - id: transit_gateway_id
    type: STRING
    defaults: tgw-0123456789abcdef0
    description: AWS Transit Gateway identifier to monitor.
  - id: max_packet_drops_threshold
    type: INT
    defaults: 100
    description: Maximum permissible dropped packets in a 15-minute window before alerting.

tasks:
  - id: query_tgw_packet_drops
    type: io.kestra.plugin.aws.cli.AwsCLI
    region: "{{ inputs.aws_region }}"
    accessKeyId: "{{ secret('AWS_ACCESS_KEY_ID') }}"
    secretKeyId: "{{ secret('AWS_SECRET_ACCESS_KEY') }}"
    commands:
      - |
        aws cloudwatch get-metric-statistics           --namespace AWS/TransitGateway           --metric-name PacketDropCount           --dimensions Name=TransitGateway,Value="{{ inputs.transit_gateway_id }}"           --start-time $(date -u -v-15m +%Y-%m-%dT%H:%M:%SZ 2>/dev/null || date -u -d "15 minutes ago" +%Y-%m-%dT%H:%M:%SZ)           --end-time $(date -u +%Y-%m-%dT%H:%M:%SZ)           --period 900           --statistics Sum           --output json > tgw_drops.json
        python3 -c "
        import json
        with open('tgw_drops.json') as f:
            dps = json.load(f).get('Datapoints', [])
        total_drops = int(sum(dp.get('Sum', 0) for dp in dps))
        result = {
            'transit_gateway_id': '{{ inputs.transit_gateway_id }}',
            'packet_drop_count': total_drops,
            'alert_triggered': total_drops > {{ inputs.max_packet_drops_threshold }}
        }
        with open('tgw_summary.json', 'w') as out:
            json.dump(result, out)
        print('Transit Gateway audit:', result)
        "
    outputFiles:
      - tgw_summary.json

  - id: evaluate_packet_drops
    type: io.kestra.plugin.core.flow.If
    condition: "{{
      fromJson(read(outputs.query_tgw_packet_drops.outputFiles['tgw_summary.jso\
      n'])).alert_triggered }}"
    then:
      - id: alert_network_team
        type: io.kestra.plugin.slack.notifications.SlackIncomingWebhook
        url: "{{ secret('SLACK_WEBHOOK') }}"
        payload: |
          {
            "text": ":warning: *AWS Transit Gateway Packet Drop Alert*: Transit Gateway `{{ inputs.transit_gateway_id }}` dropped {{ fromJson(read(outputs.query_tgw_packet_drops.outputFiles['tgw_summary.json'])).packet_drop_count }} packets in the last 15 minutes. Check route table associations, blackhole routes, or MTU mismatches."
          }

errors:
  - id: notify_sentinel_error
    type: io.kestra.plugin.slack.notifications.SlackIncomingWebhook
    url: "{{ secret('SLACK_WEBHOOK') }}"
    payload: |
      {
        "text": ":warning: *TGW Sentinel Failure*: Failed to query CloudWatch metrics for Transit Gateway `{{ inputs.transit_gateway_id }}`."
      }

triggers:
  - id: scheduled_tgw_check
    type: io.kestra.plugin.core.trigger.Schedule
    cron: "*/15 * * * *"
    disabled: true