AWS SNS，向 slack 发送“连续”通知

Question

On a high level I wrote a lambda that notifies slack when there's an error or not.

From an aws tool-chain perspective, the tech design looks like this:

Acceptance Criteria (in BDD style)

 Scenario: As an engineer I want to get notified if my lambda PASSED or FAILED whenever it executes
    Given I have a lambda function that runs on a schedule (9am everyday)
    Given I have a metric filter that looks for the string "error" in the logs
      And I created an alarm that does the following:
  # +------------------------+--------------+
  # |         ALARM                         |
  # +------------------------+--------------+
  # | Statistic              | Sum          |
  # | Period                 | 5 minutes    |
  # | Threshold type         | Static       |
  # | Alarm condition        | >= threshold |
  # | Threshold value        | 1            |
  # | Datapoints to Alarm    | 1 of 1       |
  # | missing data treatment | ignore       |
  # | Alarm State            | in Alarm     |
  # +------------------------+--------------+
      And I created another alarm that does the following:
  # +------------------------+--------------+
  # |           OK                          |
  # +------------------------+--------------+
  # | Statistic              | Sum          |
  # | Period                 | 5 minutes    |
  # | Threshold type         | Static       |
  # | Alarm condition        | <= threshold |
  # | Threshold value        | 1            |
  # | Datapoints to Alarm    | 1 of 1       |
  # | missing data treatment | good         |
  # | Alarm State            | OK           |
  # +------------------------+--------------+
     Then EVERY TIME time my function executes without "error" Then I should get "OK" 
     Then EVERY TIME time my function executes with "error" then I should get "ALARM"

The actual behavior is it will send out a notification only ONCE, and it will only send again when the alarm type changes ie

  ALARM -> OK
  OK -> ALARM

I don't seem to get notifications for this pattern

  ALARM -> ALRM
  OK -> OK

Ideally I want to receive a notification every time function executes

Answer 1

There's no need to use a CloudWatch alarm. If you want one message every time the Lambda executes, you should just publish the SNS message as the last thing inside your Lambda function.

try {

    // existing code goes here...

    snsClient.publish("my-chatbot-topic", "Some success message");
} catch (Exception e) {
    snsClient.publish("my-chatbot-topic", "Some error message");
    // rethrow the exception so that the lambda still fails for this
    throw e;
}

Answer 2

As per AWS documentations :

Alarms invoke actions for sustained state changes only. CloudWatch alarms don't invoke actions simply because they are in a particular state, the state must have changed and been maintained for a specified number of periods.

One solution is to stream the CW logs to a lambda function that sends the SNS messages. With a fast search I found this code that does exactly this (I didn't try myself): https://github.com/codemonauts/aws-cloudwatch-stream-filter-sns-gateway