Add test cases, improved error handling & logging of events

The lambda gets local tests we can use to confirm we're handling events
correctly.  In particular, events generated by Log Metrics appear to
have a slightly different format.

Response returned by the script now provides insight into the webhook
response from Slack.

We also have a new env var supported that allows us to enable incoming
event logging for all events.  Even if this is off, failure to handle an
event should still result in the event message being logged.

.gitignore

@@ -3,3 +3,4 @@ terraform.tfstate
 *.tfstate*
 terraform.tfvars
 functions/*.zip
+functions/pytest.ini

README.md

@@ -1,6 +1,6 @@
 # AWS Notify Slack Terraform module
 
-This module creates SNS topic (or use existing one) and a AWS Lambda function which sends notifications to Slack using [incoming webhooks API](https://api.slack.com/incoming-webhooks).
+This module creates an SNS topic (or uses an existing one) and an AWS Lambda function that sends notifications to Slack using the [incoming webhooks API](https://api.slack.com/incoming-webhooks).
 
 Start by setting up an [incoming webhook integration](https://my.slack.com/services/new/incoming-webhook/) in your Slack workspace.
 
@@ -11,8 +11,10 @@ Start by setting up an [incoming webhook integration](https://my.slack.com/servi
 - [x] Support plaintext and encrypted version of Slack webhook URL
 - [x] Most of Slack message options are customizable
 - [x] Support different types of SNS messages:
-  - [x] AWS Cloudwatch
+  - [x] AWS CloudWatch Alarms
+  - [x] AWS CloudWatch LogMetrics Alarms
   - [ ] [Send pull-request to add support of other message types](https://github.com/terraform-aws-modules/terraform-aws-notify-slack/pulls)
+- [x] Local pytest driven testing of the lambda to a Slack sandbox channel
 
 ## Usage
 
@@ -30,14 +32,27 @@ module "notify_slack" {
 
 ## Use existing SNS topic or create new
 
-If you want to subscribe AWS Lambda Function created by this module to an existing SNS topic you should specify `create_sns_topic = false` as argument and specify name of existing SNS topic name in `sns_topic_name`.
+If you want to subscribe the AWS Lambda Function created by this module to an existing SNS topic you should specify `create_sns_topic = false` as an argument and specify the name of existing SNS topic name in `sns_topic_name`.
 
 ## Examples
 
 * [notify-slack-simple](https://github.com/terraform-aws-modules/terraform-aws-notify-slack/tree/master/examples/notify-slack-simple) - Creates SNS topic which sends messages to Slack channel.
 * [notify-slack-kms](https://github.com/terraform-aws-modules/terraform-aws-notify-slack/tree/master/examples/notify-slack-simple) - Creates SNS topic which sends messages to Slack channel (using KMS to encrypt Slack webhook URL).
 * [cloudwatch-alerts-to-slack](https://github.com/terraform-aws-modules/terraform-aws-notify-slack/tree/master/examples/cloudwatch-alerts-to-slack) - End to end example which shows how to send AWS Cloudwatch alerts to Slack channel and use KMS to encrypt webhook URL.
 
+## Testing with pytest
+
+To run the tests:
+
+1. Set up a dedicated slack channel as a test sandbox with it's own webhook.  See [Slack Incoming Webhooks docs](https://api.slack.com/incoming-webhooks) for details.
+2. Make a copy of the sample pytest configuration and edit as needed.
+
+        cp functions/pytest.ini.sample functions/pytest.ini
+
+3. Run the tests:
+
+        pytest functions/notify_slack_test.py
+
 <!-- BEGINNING OF PRE-COMMIT-TERRAFORM DOCS HOOK -->
 
 ## Inputs
@@ -47,13 +62,14 @@ If you want to subscribe AWS Lambda Function created by this module to an existi
 | create | Whether to create all resources | string | `true` | no |
 | create_sns_topic | Whether to create new SNS topic | string | `true` | no |
 | create_with_kms_key | Whether to create resources with KMS encryption | string | `false` | no |
-| kms_key_arn | ARN of the KMS key used for decrypting slack webhook url | string | `` | no |
+| kms_key_arn | ARN of the KMS key used for decrypting slack webhook url | string | -| no |
 | lambda_function_name | The name of the Lambda function to create | string | `notify_slack` | no |
 | slack_channel | The name of the channel in Slack for notifications | string | - | yes |
 | slack_emoji | A custom emoji that will appear on Slack messages | string | `:aws:` | no |
 | slack_username | The username that will appear on Slack messages | string | - | yes |
 | slack_webhook_url | The URL of Slack webhook | string | - | yes |
 | sns_topic_name | The name of the SNS topic to create | string | - | yes |
+| log_events | Boolean flag to enabled/disable logging of incoming events | bool | `false` | no |
 
 ## Outputs
 

functions/notify_slack.py

@@ -1,4 +1,5 @@
 from __future__ import print_function
+from urllib.error import HTTPError
 import os, boto3, json, base64
 import urllib.request, urllib.parse
 import logging
@@ -59,6 +60,11 @@ def notify_slack(message, region):
         "icon_emoji": slack_emoji,
         "attachments": []
     }
+
+    if isinstance(message, str):
+        logging.info("message is a string, assuming it's JSON and decoding")
+        message = json.loads(message)
+
     if "AlarmName" in message:
         notification = cloudwatch_notification(message, region)
         payload['text'] = "AWS CloudWatch notification - " + message["AlarmName"]
@@ -69,14 +75,25 @@ def notify_slack(message, region):
 
     data = urllib.parse.urlencode({"payload": json.dumps(payload)}).encode("utf-8")
     req = urllib.request.Request(slack_url)
-    urllib.request.urlopen(req, data)
+
+    try:
+        result = urllib.request.urlopen(req, data)
+        return json.dumps({"code": result.getcode(), "info": result.info().as_string()})
+
+    except HTTPError as e:
+        logging.error("{}: result".format(e))
+        return json.dumps({"code": e.getcode(), "info": e.info().as_string()})
 
 
 def lambda_handler(event, context):
+    if 'LOG_EVENTS' in os.environ and os.environ['LOG_EVENTS'] == 'True':
+        logging.warning('Event logging enabled: `{}`'.format(json.dumps(event)))
+
     message = event['Records'][0]['Sns']['Message']
     region = event['Records'][0]['Sns']['TopicArn'].split(":")[3]
-    notify_slack(message, region)
+    response = notify_slack(message, region)
 
-    return message
+    if json.loads(response)["code"] != 200:
+        logging.error("Error: received status `{}` using event `{}` and context `{}`".format(info, event, context))
 
-#notify_slack({"AlarmName":"Example","AlarmDescription":"Example alarm description.","AWSAccountId":"000000000000","NewStateValue":"ALARM","NewStateReason":"Threshold Crossed","StateChangeTime":"2017-01-12T16:30:42.236+0000","Region":"EU - Ireland","OldStateValue":"OK"}, "eu-west-1")
+    return response

functions/notify_slack_test.py

@@ -0,0 +1,69 @@
+#!/usr/bin/env pytest
+
+import notify_slack
+import pytest
+from json import loads
+from os import environ
+
+events = (
+    (
+        {
+            "Records": [
+                {
+                    "EventSource": "aws:sns",
+                    "EventVersion": "1.0",
+                    "EventSubscriptionArn": "arn:aws:sns:eu-west-2:735598076380:service-updates:d29b4e2c-6840-9c4e-ceac-17128efcc337",
+                    "Sns": {
+                        "Type": "Notification",
+                        "MessageId": "f86e3c5b-cd17-1ab8-80e9-c0776d4f1e7a",
+                        "TopicArn": "arn:aws:sns:eu-west-2:735598076380:service-updates",
+                        "Subject": "OK: \"DBMigrationRequired\" in EU (London)",
+                        "Message": "{\"AlarmName\":\"DBMigrationRequired\",\"AlarmDescription\":\"App is reporting \\\"A JPA error occurred (Unable to build EntityManagerFactory)\\\"\",\"AWSAccountId\":\"735598076380\",\"NewStateValue\":\"OK\",\"NewStateReason\":\"Threshold Crossed: 1 datapoint [1.0 (12/02/19 15:44:00)] was not less than the threshold (1.0).\",\"StateChangeTime\":\"2019-02-12T15:45:24.006+0000\",\"Region\":\"EU (London)\",\"OldStateValue\":\"ALARM\",\"Trigger\":{\"MetricName\":\"DBMigrationRequired\",\"Namespace\":\"LogMetrics\",\"StatisticType\":\"Statistic\",\"Statistic\":\"SUM\",\"Unit\":null,\"Dimensions\":[],\"Period\":60,\"EvaluationPeriods\":1,\"ComparisonOperator\":\"LessThanThreshold\",\"Threshold\":1.0,\"TreatMissingData\":\"- TreatMissingData:                    NonBreaching\",\"EvaluateLowSampleCountPercentile\":\"\"}}",
+                        "Timestamp": "2019-02-12T15:45:24.091Z",
+                        "SignatureVersion": "1",
+                        "Signature": "WMYdVRN7ECNXMWZ0faRDD4fSfALW5MISB6O//LMd/LeSQYNQ/1eKYEE0PM1SHcH+73T/f/eVHbID/F203VZaGECQTD4LVA4B0DGAEY39LVbWdPTCHIDC6QCBV5ScGFZcROBXMe3UBWWMQAVTSWTE0eP526BFUTecaDFM4b9HMT4NEHWa4A2TA7d888JaVKKdSVNTd4bGS6Q2XFG1MOb652BRAHdARO7A6//2/47JZ5COM6LR0/V7TcOYCBZ20CRF6L5XLU46YYL3I1PNGKbEC1PIeVDVJVPcA17NfUbFXWYBX8LHfM4O7ZbGAPaGffDYLFWM6TX1Y6fQ01OSMc21OdUGV6HQR01e%==",
+                        "SigningCertUrl": "https://sns.eu-west-2.amazonaws.com/SimpleNotificationService-7dd85a2b76adaa8dd603b7a0c9150589.pem",
+                        "UnsubscribeUrl": "https://sns.eu-west-2.amazonaws.com/?Action=Unsubscribe&SubscriptionArn=arn:aws:sns:eu-west-2:735598076380:service-updates:d29b4e2c-6840-9c4e-ceac-17128efcc337",
+                        "MessageAttributes": {}
+                    }
+                }
+            ]
+        }
+    ),
+    (
+        {
+            "AlarmName": "Example",
+            "AlarmDescription": "Example alarm description.",
+            "AWSAccountId": "000000000000",
+            "NewStateValue": "ALARM",
+            "NewStateReason": "Threshold Crossed",
+            "StateChangeTime": "2017-01-12T16:30:42.236+0000",
+            "Region": "EU - Ireland",
+            "OldStateValue": "OK"
+        }
+    )
+)
+
+
+@pytest.fixture(scope='module', autouse=True)
+def check_environment_variables():
+    required_environment_variables = ("SLACK_CHANNEL", "SLACK_EMOJI", "SLACK_USERNAME", "SLACK_WEBHOOK_URL")
+    missing_environment_variables = []
+    for k in required_environment_variables:
+        if k not in environ:
+            missing_environment_variables.append(k)
+
+    if len(missing_environment_variables) > 0:
+        pytest.exit('Missing environment variables: {}'.format(", ".join(missing_environment_variables)))
+
+
+@pytest.mark.parametrize("event", events)
+def test_lambda_handler(event):
+    if 'Records' in event:
+        response = notify_slack.lambda_handler(event, 'self-context')
+
+    else:
+        response = notify_slack.notify_slack(event, 'eu-west-1')
+
+    response = loads(response)
+    assert response['code'] == 200

functions/pytest.ini.sample

@@ -0,0 +1,8 @@
+[pytest]
+addopts = --disable-pytest-warnings
+env =
+  SLACK_CHANNEL=slack_testing_sandbox
+  SLACK_EMOJI=:aws:
+  SLACK_USERNAME=notify_slack_test
+  SLACK_WEBHOOK_URL=https://hooks.slack.com/services/YOUR/WEBOOK/URL
+

functions/requirements.txt

@@ -0,0 +1,4 @@
+boto3
+
+pytest
+pytest-env

main.tf

@@ -60,6 +60,7 @@ resource "aws_lambda_function" "notify_slack" {
       SLACK_CHANNEL     = "${var.slack_channel}"
       SLACK_USERNAME    = "${var.slack_username}"
       SLACK_EMOJI       = "${var.slack_emoji}"
+      LOG_EVENTS        = "${var.log_events ? "True" : "False"}"
     }
   }
 

variables.tf

@@ -44,6 +44,11 @@ variable "kms_key_arn" {
   default     = ""
 }
 
+variable "log_events" {
+  description = "Boolean flag to enabled/disable logging of incoming events"
+  default     = false
+}
+
 locals {
   module_relpath = "${substr(path.module, length(path.cwd) + 1, -1)}"
 }