title: AWS Cloudwatch Metric Alarm not triggering after first time
body: <p>I have a alarm looking for <code>error</code> message in logs and it does trigger alarm state. But it doesn't get reset and remains in <code>In Alarm</code> state. I have the alarm action as SNS topic which in turn triggers email. So basically after first error I don't see any subsequent email. What's going wrong with the following template config?</p>
  
  <pre><code>"AppErrorMetric": {
    "Type": "AWS::Logs::MetricFilter",
    "Properties": {
      "LogGroupName": {
        "Ref": "AppServerLG"
      },
      "FilterPattern": "[error]",
      "MetricTransformations": [
        {
          "MetricValue": "1",
          "MetricNamespace": {
            "Fn::Join": [
              "",
              [
                {
                  "Ref": "ApplicationEndpoint"
                },
                "/metrics/AppError"
              ]
            ]
          },
          "MetricName": "AppError"
        }
      ]
    }
  },
  "AppErrorAlarm": {
          "Type": "AWS::CloudWatch::Alarm",
          "Properties": {
      "ActionsEnabled": "true",
              "AlarmName": {
                  "Fn::Join": [
                      "",
                      [
                          {
                              "Ref": "AppId"
                          },
                          ",",
                          {
                              "Ref": "AppServerAG"
                          },
                          ":",
                          "AppError",
                          ",",
                          "MINOR"
                      ]
                  ]
              },
              "AlarmDescription": {
                  "Fn::Join": [
                      "",
                      [
                          "service is throwing error. Please check logs.",
                          {
                              "Ref": "AppServerAG"
                          },
                          "-",
                          {
                              "Ref": "AppId"
                          }
                      ]
                  ]
              },
              "MetricName": "AppError",
              "Namespace": {
                  "Fn::Join": [
                      "",
                      [
                          {
                              "Ref": "ApplicationEndpoint"
                          },
                          "metrics/AppError"
                      ]
                  ]
              },
              "Statistic": "Sum",
              "Period": "300",
              "EvaluationPeriods": "1",
              "Threshold": "1",
              "AlarmActions": [{
                "Fn::GetAtt": [
                  "VPCInfo",
                  "SNSTopic"
                ]
              }],
              "ComparisonOperator": "GreaterThanOrEqualToThreshold"
          }
  }
  </code></pre>