cloudwatch_log_based_alarm.tf

# metric creation for the cloudwatch logs
resource "aws_cloudwatch_log_metric_filter" "cloudwatch_filter" {
  name           = "MyLogFilter"
  log_group_name = "/aws/ecs/my-service"
  pattern        = "This text should trigger alarm"
  metric_transformation {
    name      = "MyLogMetric"
    namespace = "MyLogNamespace"
    value     = "1"
  }
}

# cloudwatch alarm for the metric
resource "aws_cloudwatch_metric_alarm" "cloudwatch_logs_alarm" {

  alarm_name         = "MyLogBasedAlarm"
  alarm_description  = "Alarm triggered by Cloudwatch Log ..."
  alarm_actions      = var.alarm_actions
  treat_missing_data = "missing"

  metric_name         = lookup(aws_cloudwatch_log_metric_filter.cloudwatch_filter.metric_transformation[0], "name")
  threshold           = "10"
  statistic           = "Sum"
  comparison_operator = "GreaterThanThreshold"
  datapoints_to_alarm = "1"
  evaluation_periods  = "1"
  period              = "300"
  namespace           = lookup(aws_cloudwatch_log_metric_filter.cloudwatch_filter.metric_transformation[0], "namespace")

  tags = var.tags
}