(AWS Lambda) Send ECS Task events to CloudWatch Logs

ecs-task-events-to-cloudwatch-logs.py

# This lambda function can be linked with CloudWatch events to send Task state changes to
# a CloudWatch Logs stream
#
# This is highly recommended as, in my experience, the API does *NOT* return all state change
# events; this is the only way to reliably see them all

import os
import time
import json
import boto3

def handler(event, context):
  if event['source'] != 'aws.ecs':
     raise ValueError("Function only supports input from events with a source type of: aws.ecs")

  group = ''
  stream = ''

  if event['detail-type'] == 'ECS Task State Change':
    group = os.environ['TASK_EVENTS_GROUP']
    stream = event['detail']['group'].replace(':', '/') + '/' + event['detail']['taskArn'].split('/')[1]
  else:
    raise ValueError("Only Task State Change events are supported")

  client = boto3.client('logs')
  response = client.describe_log_streams(logGroupName=group,logStreamNamePrefix=stream)
  logStreams = response['logStreams']
  sequenceToken = None

  if logStreams:
    logStream = logStreams[0]

    if 'uploadSequenceToken' in logStream:
      sequenceToken = logStream['uploadSequenceToken']
  else:
    client.create_log_stream(logGroupName=group,logStreamName=stream)

  logEvents = [
    {
      'timestamp': int(round(time.time() * 1000)),
      'message': json.dumps(event)
    },
  ]

  if sequenceToken:
    client.put_log_events(
      logGroupName=group,
      logStreamName=stream,
      sequenceToken=sequenceToken,
      logEvents=logEvents
    )
  else:
    client.put_log_events(logGroupName=group, logStreamName=stream, logEvents=logEvents)