Create a periodical program with Ruby x AWS Lambda x CloudWatch Events

Configuration aimed at in this article

Launch Lambda triggered by CloudWatch Events and send a message to Slack.

• Set the execution schedule in advance using the Cron formula for CloudWatch Events.

↑ It will be automatically executed regularly like this.

Target audience

--People who want to create a periodical execution program in Ruby --People who want to touch Lambda

specification

Language: Ruby 2.5 series Infrastructure: Lambda, ClowdWatch Events

• Please create your own SlackBot in advance.

See also: Creating a bot for your workspace (https://slack.com/intl/ja-jp/help/articles/115005265703-%E3%83%AF%E3%83%BC%E3%82% AF% E3% 82% B9% E3% 83% 9A% E3% 83% BC% E3% 82% B9% E3% 81% A7% E5% 88% A9% E7% 94% A8% E3% 81% 99% E3% 82% 8B% E3% 83% 9C% E3% 83% 83% E3% 83% 88% E3% 81% AE% E4% BD% 9C% E6% 88% 90)

Completed form

periodic-slack-bot-on-aws-lambda

• If you have trouble making from scratch, please git clone from ↑.

Create a program

Create a program to send messages to Slack.

Create directory

$ mkdir periodic-slack-bot-on-aws-lambda
$ cd periodic-slack-bot-on-aws-lambda

Set Git

$ git init
$ touch .gitignore

:./.gitignore

.bundle
/vendor/bundle

Describe what you don't want to manage with Git.

Specify Ruby version

$ rbenv local 2.5.1 
# 2.5 series recommended

Install Gem

$ bundle init

Create a Gemfile with the ↑ command and edit it as follows.

./Gemfile

# frozen_string_literal: true

source "https://rubygems.org"

git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }

ruby '2.5.1'

gem 'async-websocket'
gem 'slack-ruby-bot'

Then install the required Gem.

$ bundle install --path vendor/bundle

• Since it is necessary to package the Gem in a zip file later, it must be installed under "vendor / bundle" (local) instead of globally.

Create app.rb

$ touch app.rb

ruby:./app.rb

require 'slack-ruby-client'

Slack.configure do |conf|
  conf.token = ENV['SLACK_BOT_TOKEN']
end

def post_to_slack(event:, context:)
  client = Slack::Web::Client.new
  client.chat_postMessage(channel: ENV['SLACK_CHANNEL_NAME'], text: 'Test submission from AWS Lambda', as_user: true)
end

• Note that it will not work unless you pass "(event :, context :)" as an argument. Reference article: AWS Lambda function handler for Python

Deploy to Lambda

After creating the program, prepare to deploy it to Lambda.

Install AWS CLI

This time, we will deploy using a tool called "AWS CLI", so if you haven't installed it yet, install it.

$ brew install awscli

Create an IAM user

Create an IAM user for deployment. First, go to "IAM"-> "Policy"-> "Create Policy" and paste the following statement from the JSON tab.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "apigateway:*",
                "cloudformation:*",
                "dynamodb:*",
                "events:*",
                "iam:*",
                "lambda:*",
                "logs:*",
                "route53:*",
                "s3:*"
             ],
            "Resource": [
                "*"
            ]
        }
    ]
}

See also: Minimal Deploy IAM Policy (https://rubyonjets.com/docs/extras/minimal-deploy-iam/)

Enter the policy name and description as appropriate, and click "Create Policy".

Next, go to "IAM"-> "User"-> "Create User", give it an appropriate name, check "Access by Program", and proceed to the next.

Select the "Minimal Deploy IAM Policy" created earlier from "Attach existing policy directly" and proceed to the next.

(Tags are optional) A confirmation screen will be displayed at the end, so if there are no problems, click "Create User".

Then, two "access key ID" and "secret access key" will be issued, so keep it in a safe place as you download the csv file or make a note of it.

AWS CLI settings

$ aws configure --profile lambda (any profile name is OK)

AWS Access Key ID #Access key ID created earlier
AWS Secret Access Key #The secret access key you created earlier
Default region name # ap-northeast-1 
Default output format # json 

When you type "aws configure" in the terminal, you will be asked various things interactively, so enter the necessary information for each.

Create function

Open "AWS Lambda" from the AWS console screen and click "Create Function".

--Function name (arbitrary name) --Runtime (Ruby2.5)

To create a function. (Others are OK with default values or blanks)

From "Edit environment variables"

• SLACK_BOT_TOKEN
• SLACK_CHANNEL_NAME

Set environment variables for each.

Changed the handler name from "Edit basic settings" to "app.post_to_slack (file name.method name)".

Deploy

Package the created program as a zip file.

$ zip -r function.zip app.rb vendor

Deploy using aws cli.

$ aws lambda update-function-code --function-name PeriodicSlackBotOnAwsLambda --zip-file fileb://function.zip --profile lambda

{
    "FunctionName": "PeriodicSlackBotOnAwsLambda",
    "FunctionArn": "arn:aws:lambda:ap-northeast-1:**************:function:PeriodicSlackBotOnAwsLambda",
    "Runtime": "ruby2.5",
    "Role": "arn:aws:iam::**************:role/service-role/PeriodicSlackBotOnAwsLambda-role-**************",
    "Handler": "app.post_to_slack",
    "CodeSize": 12941753,
    "Description": "",
    "Timeout": 3,
    "MemorySize": 128,
    "LastModified": "2020-10-09T21:08:11.888+0000",
    "CodeSha256": "**************/**************=",
    "Version": "$LATEST",
    "Environment": {
        "Variables": {
            "SLACK_CHANNEL_NAME": "#**************",
            "SLACK_BOT_TOKEN": "xoxb-**************-**************-**************"
        }
    },
    "TracingConfig": {
        "Mode": "PassThrough"
    },
    "RevisionId": "********-****-****-****-********",
    "State": "Active",
    "LastUpdateStatus": "Successful"
}

• Set the function name created earlier in --function-name.

Test run

Create an appropriate test from "Test event settings". (Hash can be left blank)

Click "Test" and if the message is sent to the specified Slack channel, it is successful.

Schedule management with CloudWatch Events

Trigger settings

Click "Add Trigger".

--Trigger name: CloudWatch Events --Rule: Create a new rule --Rule name: test_30minutes (optional) --Rule description: Run once every 30 minutes (optional) --Rule type: Schedule expression --Schedule expression: cron (* / 30 * * *? *)

• Set the execution interval as you like.

The explanation of how to write a cron expression is omitted this time. Reference: Try touching cron

Wait for the passage of time, and if it is executed regularly, it will be successful.

If it doesn't work, the log should be output in the CloudWatch log group, so debug it appropriately.

Afterword

Thank you for your hard work! If you proceed according to the article and there is a part that does not work well, I would appreciate it if you could point it out in the comment orchid.