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Support for CloudWatch Metric Math Alarms #44

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f5a6c3e
Updated CloudWatch Alarm handling to support metric math alarms
bobwilkinson20 Aug 7, 2019
985d519
Added metric math alarm test case
bobwilkinson20 Aug 7, 2019
5e4123c
Addressing Comments on the Pull Request
bobwilkinson20 Aug 8, 2019
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30 changes: 25 additions & 5 deletions index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -233,12 +233,33 @@ var handleCloudWatch = function(event, context) {
var region = event.Records[0].EventSubscriptionArn.split(":")[3];
var subject = "AWS CloudWatch Notification";
var alarmName = message.AlarmName;
var metricName = message.Trigger.MetricName;
var trigger = message.Trigger;
var alarmExpression;
if (typeof trigger.MetricName === "undefined") {
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@quisido quisido Aug 8, 2019

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If trigger.MetricName and trigger.Metrics are mutually exclusive, it may improve readability to say "If this trigger has multiple metrics, use them" instead of "If this trigger doesn't have a single metric, use multiple." if (typeof trigger.Metrics === 'object') will determine if trigger.Metrics is an array.

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@quisido quisido Aug 8, 2019

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There's also Array.isArray(trigger.Metrics) instead of checking typeof. While it is a part of the ES5 spec, older browser has spotty implementations. NodeJS should not have a problem with it. If you find that ES6 is acceptable for this file, Array.isArray should be acceptable as well.

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@bobwilkinson20 bobwilkinson20 Aug 8, 2019

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changed to if (typeof trigger.Metrics === 'object')

// This is a CloudWatch metric math alarm. Instead of a MetricName and
// statistic there is an array of Metrics where the first element is the
// math expression.

// first build a dictionary mapping metric ids to metric name and statistic
var sourceMetrics = {};
for (const metric of trigger.Metrics.slice(1)) {
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const and for...of loops are ES6, but the rest of this file seems to be using ES5 (e.g. var instead of let or const). I'd make sure ES6 is supported and that ES5 is not otherwise a requirement. It is odd to see both in one file.

As ES5, this would be:

var triggerMetricsLength = trigger.Metrics.length;
for (var i = 1; i < triggerMetricsLength; i++) {
  var metric = trigger.Metrics[i];
  // ...
}

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@bobwilkinson20 bobwilkinson20 Aug 8, 2019

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combined this change with below recommendation

sourceMetrics[metric.Id] = metric.MetricStat.Stat + ":"
+ metric.MetricStat.Metric.MetricName;
}

// now replace each instance of the metric id in the alarm expression
alarmExpression = trigger.Metrics[0].Expression;
for (var metricid in sourceMetrics) {
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for...in loops should be avoided. If you are just trying to get the metric.Ids, this loop can probably be a copy of or merged with the previous.

alarmExpression = trigger.Metrics[0].Expression;
var triggerMetricsLength = trigger.Metrics.length;
for (var i = 1; i < triggerMetricsLength; i++) {
  var metric = trigger.Metrics[i];
  alarmExpression = alarmExpression.replace(
    new RegExp(metric.Id, 'g'),
    metric.MetricStat.Stat + ':' + metric.MetricStat.Metric.MetricName
  );
}

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@bobwilkinson20 bobwilkinson20 Aug 8, 2019

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great suggestion - adopted this logic

alarmExpression = alarmExpression.replace(new RegExp(metricid,"g"),sourceMetrics[metricid]);
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@quisido quisido Aug 8, 2019

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If metric.Id is not intended to be a regular expression itself, it should probably be escaped. As is, a malicious user can submit a custom, unsanitized regular expression as input, which may produce undesirable effects if we parse it.

function sanitizeStringForRegExp(str) {
  return str.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
}
alarmExpression = alarmExpression.replace(
  new RegExp(sanitizeStringForRegExp(metricid), 'g'),
  sourceMetrics[metricid]
);

Source: Stack Overflow

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@bobwilkinson20 bobwilkinson20 Aug 8, 2019

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incorporated escape-string-regexp package which implements the equivalent of sanitizeStringForRegExp above.

}
} else {
// This is a standard CloudWatch alarm on a single metric
alarmExpression = trigger.Statistic + ":" + trigger.MetricName;
}
var oldState = message.OldStateValue;
var newState = message.NewStateValue;
var alarmDescription = message.AlarmDescription;
var alarmReason = message.NewStateReason;
var trigger = message.Trigger;
var color = "warning";

if (message.NewStateValue === "ALARM") {
Expand All @@ -257,8 +278,7 @@ var handleCloudWatch = function(event, context) {
{ "title": "Alarm Description", "value": alarmDescription, "short": false},
{
"title": "Trigger",
"value": trigger.Statistic + " "
+ metricName + " "
"value": alarmExpression + " "
+ trigger.ComparisonOperator + " "
+ trigger.Threshold + " for "
+ trigger.EvaluationPeriods + " period(s) of "
Expand Down Expand Up @@ -364,7 +384,7 @@ var processEvent = function(event, context) {
try {
eventSnsMessage = JSON.parse(eventSnsMessageRaw);
}
catch (e) {
catch (e) {
}

if(eventSubscriptionArn.indexOf(config.services.codepipeline.match_text) > -1 || eventSnsSubject.indexOf(config.services.codepipeline.match_text) > -1 || eventSnsMessageRaw.indexOf(config.services.codepipeline.match_text) > -1){
Expand Down
2 changes: 1 addition & 1 deletion package.json
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Expand Up @@ -2,7 +2,7 @@
"name": "lambda-cloudwatch-slack",
"version": "0.3.0",
"description": "Better Slack notifications for AWS CloudWatch",
"authors": [
"authors": [
"Christopher Reichert <creichert07@gmail.com>",
"Cody Reichert <codyreichert@gmail.com>",
"Alexandr Promakh <s-promakh@ya.ru>"
Expand Down
3 changes: 2 additions & 1 deletion scripts/test.sh
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Expand Up @@ -5,9 +5,10 @@ $NODE_LAMBDA run -x test/context.json -j test/sns-codepipeline-event-stage-start
$NODE_LAMBDA run -x test/context.json -j test/sns-codepipeline-event-stage-succeeded.json
$NODE_LAMBDA run -x test/context.json -j test/sns-codepipeline-event-stage-failed.json
$NODE_LAMBDA run -x test/context.json -j test/sns-cloudwatch-event.json
$NODE_LAMBDA run -x test/context.json -j test/sns-cloudwatch-event-metricmath.json
$NODE_LAMBDA run -x test/context.json -j test/sns-event.json
$NODE_LAMBDA run -x test/context.json -j test/sns-elastic-beanstalk-event.json
$NODE_LAMBDA run -x test/context.json -j test/sns-codedeploy-event.json
$NODE_LAMBDA run -x test/context.json -j test/sns-codedeploy-configuration.json
$NODE_LAMBDA run -x test/context.json -j test/sns-elasticache-event.json
$NODE_LAMBDA run -x test/context.json -j test/sns-autoscaling-event.json
$NODE_LAMBDA run -x test/context.json -j test/sns-autoscaling-event.json
18 changes: 18 additions & 0 deletions test/sns-cloudwatch-event-metricmath.json
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@@ -0,0 +1,18 @@
{
"Records": [
{
"EventSource": "aws:sns",
"EventVersion": "1.0",
"EventSubscriptionArn": "arn:aws:sns:us-east-1:123456789123:cloudwatch-alarms:00000000-0000-0000-0000-000000000000",
"Sns": {
"Type": "Notification",
"MessageId": "00000000-0000-0000-0000-000000000000",
"TopicArn": "arn:aws:sns:us-east-1:123456789123:cloudwatch-alarms",
"Subject": "ALARM: \"Sample Metric Math Alert\" in US East (N. Virginia)",
"Message": "{\"AlarmName\":\"Sample Metric Math Alert\",\"AlarmDescription\":null,\"AWSAccountId\":\"946184294613\",\"NewStateValue\":\"ALARM\",\"NewStateReason\":\"Threshold Crossed: 1 out of the last 1 datapoints [8133.333333333447 (07/08/19 18:43:00)] was greater than the threshold (1000.0) (minimum 1 datapoint for OK -> ALARM transition).\",\"StateChangeTime\":\"2019-08-07T18:45:24.269+0000\",\"Region\":\"US East (N. Virginia)\",\"OldStateValue\":\"OK\",\"Trigger\":{\"Period\":60,\"EvaluationPeriods\":1,\"ComparisonOperator\":\"GreaterThanThreshold\",\"Threshold\":1000.0,\"TreatMissingData\":\"- TreatMissingData: missing\",\"EvaluateLowSampleCountPercentile\":\"\",\"Metrics\":[{\"Expression\":\"m1*100*m2 - MIN(m1)\",\"Id\":\"e2\",\"Label\":\"Expression2\",\"ReturnData\":true},{\"Id\":\"m1\",\"MetricStat\":{\"Metric\":{\"Dimensions\":[{\"value\":\"i-0a5c8ea70646e7b05\",\"name\":\"InstanceId\"}],\"MetricName\":\"CPUUtilization\",\"Namespace\":\"AWS/EC2\"},\"Period\":60,\"Stat\":\"Average\"},\"ReturnData\":false},{\"Id\":\"m2\",\"MetricStat\":{\"Metric\":{\"Dimensions\":[{\"value\":\"i-0a5c8ea70646e7b05\",\"name\":\"InstanceId\"}],\"MetricName\":\"NetworkOut\",\"Namespace\":\"AWS/EC2\"},\"Period\":60,\"Stat\":\"Average\"},\"ReturnData\":false}]}}",
"Timestamp": "2019-08-07T18:45:24.355Z",
"MessageAttributes": {}
}
}
]
}