Introduction

You can set billing alerts on CloudWatch, but as a super-worried person, I would like to check the billing amount from the beginning of the month to the day before by email every day. There were many ways to notify Slack channels using AWS Lambda and webhooks, but there weren't many ways to notify by email, so I've summarized them.

Overview

Get the bill from Cost Explorer.

There is also a method to obtain from CloudWatch, but since there was information that there is a difference between the two and the correct value is Cost Explorer, I decided to use Cost Explorer. Did.

The runtime of the Lambda function is Python 3.7, and the AWS SDK (Boto3) for Python is used.
Use the Lambda function with the trigger to get the total billing amount from the beginning of the month to the day before and the billing amount for each service, format the contents, and publish it as a message on the Amazon SNS topic.
The SNS topic that received the message sends the message to the associated endpoint (email address).

Understanding of terms

In particular, the terms that appear in Amazon SNS and their relationships were complicated, so I will summarize them very roughly.

** ARN **: A name that uniquely identifies your AWS resource.
** Topic **: Ability to group multiple endpoints (here email addresses).
** Endpoint **: Delivery destination. This time it will be your email address.
** Subscription **: Associate topics with endpoints

For a deeper understanding, the terminology section of the following article was very helpful, so it is recommended that you read it carefully in advance.

Basic knowledge for sending push notifications on Amazon SNS | UNITRUST

Setting method

Enable Cost Explorer

If you haven't enabled Cost Explorer, enable it from My Billing Dashboard (https://console.aws.amazon.com/billing/home#/costexplorer).

1.Cost Explorer.png

Creating SNS topics

Go to the Amazon SNS service screen.

Available regions are limited. (Supported Regions and Countries-Amazon Simple Notification Service)

From the "Topic" menu, press "Create Topic". 2-1.トピックメニュー.png

Enter "Name" and "Display name" and press "Create topic".

The "display name" set here will be the ** email sender name **.
By the way, as a topic for notifying the administrator, the name is "** sendMailAdmin " and the display name is " Administrator", assuming that it will be used for distribution for other purposes in the future. I have made a general-purpose notification email ** ".

Subscription creation

Create a subscription (+ endpoint).

Click "Create Subscription".

Make a note of the ** ARN ** displayed on the screen.

Enter the following items and press "Create Subscription".

"Topic ARN" should be automatically entered, but if not, enter the topic ARN that you wrote down.

item name	Input value / selection value
Topic ARN	ARN of the topic you wrote down
protocol	Email
end point	Received email address

3-2.サブスクリプションの作成.png

Subscription Approval

A confirmation email will be sent to the email address specified for the endpoint with the subject "AWS Notification --Subscription Confirmation", so press "Confirm subscription".

4-1.認証メール.png 4-2.認証メール.png

The status of the subscription associated with the topic will be "Confirmed". 4-3.認証メール.png

Creating a Lambda function

You have created a topic subscription endpoint.

When you issue a message to the ARN of a topic, the message will be delivered to the endpoint (email address) associated with this topic. So next, create a Lambda function that will generate a message to issue to the topic's ARN. First, press "Create Function" from the AWS Lambda dashboard.

5-1.Lambda関数.png

Confirm that the option is "Create from scratch", enter the following in "Basic information", and press "Create function".

Click "** Select or create execution role " in "Access permissions" and select " Create new role from AWS policy template **".

item name	Input value / selection value
Function name	sendCost (with any name you like)
runtime	Python 3.7
Role name	SNSServiceRoleForLambda (with any name you like)
Policy template	Amazon SNS Issuance Policy

5-2.Lambda関数.png

Lambda function test

Next, we will write the code to acquire the billing information, but to confirm the settings so far, first we will write the process to issue a test message. Enter the following code in the "Function Code" field at the bottom after creating the function.

For TopicArn, set ** ARN ** that you wrote down when creating the SNS topic.

`lambda_function.py`


import boto3

def lambda_handler(event, context):
	sns = boto3.client('sns')
	subject = 'The subject of the test email from Lambda.'
	message = 'This is the body of the test email from Lambda.'

	response = sns.publish(
    	TopicArn = 'arn:aws:sns:*:*:*',
    	Subject = subject,
    	Message = message
	)

	return response

And, in reality, it will be executed periodically with a trigger, but I will try to send it manually.

After pressing "Save" at the top right of the screen, press "Test", enter an appropriate name in "Event Name", and press "Create". Others can be left at their default values.

5-3.Lambda関数.png

When you return to the original screen and click "Test" on the upper right again, the function will be executed and the email should have arrived at the specified incoming email address. 5-4.Lambda関数.png

If you do not receive it, check whether an error message is displayed on the console (Execution results) at the bottom of the code entry field, and whether the entered ARN is correct.

Code creation for billing information notification

Finally, I will write the code to get the billing amount from Cost Explorer and notify it on Amazon SNS. For TopicArn, set the ARN that you wrote down when creating the SNS topic as before.

** * As will be described later, an error will occur even if you test without making additional settings! ** **

The code is based on the Developers.IO article.

`lambda_function.py`


import boto3
from datetime import datetime, timedelta, date

def lambda_handler(event, context):
    ce = boto3.client('ce')
    sns = boto3.client('sns')

    #Get the total bill for this month
    total_billing = get_total_billing(ce)
    #Get the total billing amount for this month (for each service)
    service_billings = get_service_billings(ce)

    #Generate a message to publish to an Amazon SNS topic
    (subject, message) = get_message(total_billing, service_billings)

    response = sns.publish(
        TopicArn = 'arn:aws:sns:*:*:*',
        Subject = subject,
        Message = message
    )

    return response

def get_total_billing(ce):
    (start_date, end_date) = get_total_cost_date_range()

    response = ce.get_cost_and_usage(
        TimePeriod={
            'Start': start_date,
            'End': end_date
        },
        Granularity='MONTHLY',
        Metrics=[
            'AmortizedCost'
        ]
    )

    return {
        'start': response['ResultsByTime'][0]['TimePeriod']['Start'],
        'end': response['ResultsByTime'][0]['TimePeriod']['End'],
        'billing': response['ResultsByTime'][0]['Total']['AmortizedCost']['Amount'],
    }

def get_service_billings(ce):
    (start_date, end_date) = get_total_cost_date_range()

    response = ce.get_cost_and_usage(
        TimePeriod={
            'Start': start_date,
            'End': end_date
        },
        Granularity='MONTHLY',
        Metrics=[
            'AmortizedCost'
        ],
        GroupBy=[
            {
                'Type': 'DIMENSION',
                'Key': 'SERVICE'
            }
        ]
    )

    billings = []

    for item in response['ResultsByTime'][0]['Groups']:
        billings.append({
            'service_name': item['Keys'][0],
            'billing': item['Metrics']['AmortizedCost']['Amount']
        })

    return billings


def get_total_cost_date_range():
    start_date = date.today().replace(day=1).isoformat()
    end_date = date.today().isoformat()

    # get_cost_and_usage()Since the same date cannot be specified for start and end of, if today is 1st, it will be in the range from "1st of last month to 1st of this month (today)"
    if start_date == end_date:
        end_of_month = datetime.strptime(start_date, '%Y-%m-%d') + timedelta(days=-1)
        begin_of_month = end_of_month.replace(day=1)
        return begin_of_month.date().isoformat(), end_date
    return start_date, end_date


def get_message(total_billing, service_billings):
    start = datetime.strptime(total_billing['start'], '%Y-%m-%d').strftime('%Y/%m/%d')

    #Since the End date is not included in the result, it should be the day before on the display.
    end_today = datetime.strptime(total_billing['end'], '%Y-%m-%d')
    end_yesterday = (end_today - timedelta(days=1)).strftime('%Y/%m/%d')

    total = round(float(total_billing['billing']), 2)
    subject = f'{start}～{end_yesterday}Billing amount:${total:.2f}'

    message = []
    message.append('[Breakdown]')
    for item in service_billings:
        service_name = item['service_name']
        billing = round(float(item['billing']), 2)

        if billing == 0.0:
            #If there is no request, the breakdown will not be displayed
            continue
        message.append(f'・{service_name}: ${billing:.2f}')

    return subject, '\n'.join(message)

I think this is complete, but ** the role assigned to Lamda does not have permission to access Cost Explorer **, so the following error occurs.

"errorMessage": "An error occurred (AccessDeniedException) when calling the GetCostAndUsage operation: User: arn:aws:sts::251745928455:assumed-role/SNSServiceRoleForLambda/sendCost is not authorized to perform: ce:GetCostAndUsage on resource: arn:aws:ce:us-east-1:251745928455:/GetCostAndUsage"

Therefore, on the IAM management screen, attach a policy that can access Cost Explorer to the role.

There seems to be a way to select "Create custom role" when creating a function and assign policies at once with json, but as of May 2020, it was not an option.

Create and attach policies

First, display Policy list on IAM management screen and press "Create policy".

6-1.ポリシー作成.png

Enter the following items and press "Confirm Policy".

item name	Input value / selection value
service	Cost Explorer Service
action	Search for "Get Cost And Usage" and check it

6-2ポリシー作成.png

On the policy confirmation screen, enter "Name" and press "Create Policy".

Here, the name is "** AmazonCostExplorerGetCostAccess **".

6-3.ポリシー作成.png

Go to the Role List screen (https://console.aws.amazon.com/iam/home#/roles) and select the role you assigned to Lambda.

6-4.ポリシー作成.png

Click "Attach policy".

6-5.ポリシー作成.png

In "Policy Filter", enter the name you set when creating the policy and search ("AmazonCostExplorerGetCostAccess" in the example of this article), check the hits, and press "Attach Policy".

6-6.ポリシー作成.png

Execution of Lambda function

Now that the function can be executed normally, click "Test" at the top right of the setting screen of the created function.

7-1.Lambda関数.png

If everything is set up correctly, you should receive an email like the one below.

7-2.メール.png

Trigger settings

Finally, set a trigger to notify you by email at a fixed time every day. Press "Add Trigger" on the left side of the function setting screen. 8-1.トリガーの設定.png

Set as follows and press "Add".

item name	Input value / selection value
Select a trigger	CloudWatch Events/EventBridge
rule	新規ruleの作成
Rule name	sendDailyCost (appropriately)
Rule type	Schedule formula
Schedule formula	cron(0 14 ? * * *）
Trigger activation	To check

This time I set it at 23:00. Note that the time is set in UTC, so set the time **, which is obtained by subtracting 9 hours from JST (Japan Standard Time) **. 8-2.トリガーの設定.png

After that, please make sure that you receive the email at the specified time every day.

Now you can sleep with peace of mind every day!

Reference information / citation

Email daily AWS bills on Lambda x Amazon SNS

Introduction

Overview

Understanding of terms

Setting method

Enable Cost Explorer

Creating SNS topics

Subscription creation

Subscription Approval

Creating a Lambda function

Lambda function test

lambda_function.py

Code creation for billing information notification

lambda_function.py

Create and attach policies

Execution of Lambda function

Trigger settings

Reference information / citation

`lambda_function.py`

`lambda_function.py`