Cloudwatch Alarm to Slack

Basic AWS lambda function use to raise received notifications to Slack.

Notification originates from Cloudwatch Alarm -> SNS -> Lambda

Lambda

Expects either SLACK_WEBHOOK_URL or SLACK_WEBHOOK_SECRET env var to raise notifications:

• SLACK_WEBHOOK_URL - Webook URL value
• SLACK_WEBHOOK_SECRET - AWS SecretsManager Id containing webook URL as plain text.

If not supplied it will print payload that would be sent to Slack. If both supplied SLACK_WEBHOOK_URL takes precedence.

Parses incoming SNS message and POSTs to above webhook url.

See sample.json for example data, this allows the main.py to be run locally.

See package.sh to build zip file with dependencies

Terraform

Terraform creates:

• Lambda function
• SNS Topic
• SNS Topic subscription to Lambda
• SNS Topic policy to allow Cloudwatch Alarms to publish
• if SLACK_WEBHOOK_SECRET provided:
  • AWS Parameters and Secrets Lambda Extension layer is added
  • Permissions for Lambda execution policy to read secret

Variables

Variable	Description	Default
s3_bucket	S3 bucket containing cloudwatch-to-slack Lambda function
s3_key	S3 key for cloudwatch-to-slack Lambda function
sns_topic_arn	ARN of topic that will trigger Lambda
prefix	Prefix for services
slack_webhook_url	Slack webhook URL to call (optional)
slack_webhook_secret	AWS SecretsManager secret storing Slack webhook URL to call (optional)
runtime	Python runtime to use for lambda	python3.11
dead_letter_arn	(Optional) ARN of SNS topic or SQS queue to notify if invocation fails
ssm_layer_account_id	AccountId to use for accessing AWS Parameters and Secrets Lambda Extension	015030872274
ssm_layer_version	Version of AWS Parameters and Secrets Lambda Extension to use	12

AWS Parameters and Secrets Lambda Extension

As noted above, if slack_webhook_secret is provided then AWS Parameters and Secrets Lambda Extension is added to function.

The ssm_layer_account_id and ssm_layer_version variable is defaulted to use values appropriate for eu-west-1 region. If using a different region then these value will need to be updated. See AWS docs for this.

Note

Attempts to use to reference aws_lambda_layer_version to find the above failed.

Outputs

Variable	Description
sns_topic_arn	ARN of SNS topic for handling Cloudwatch Alarm
role_arn	ARN of lambda role