Serverless: Lambda + DynamoDB

How to deploy

Create Lambda function

1. Open the Functions page on the lambda console
2. Creat funciton -> Author from scratch.
3. Choose a name, e.g. telegramBotTengeEuro.
4. Runtime: Python 3.8.
5. Keep rest at default for now and press Create fundtion.

Create a web API with an HTTP endpoint for the Lambda function

Reference: https://docs.aws.amazon.com/lambda/latest/dg/services-apigateway.html

1. Open the Functions page on the Lambda console.
2. Choose the function.
3. Under Functional overview, choose Add trigger.
4. Select API Gateway.
5. For API, choose Create an API.
6. For API Type, choose HTTP API.
7. For Security, choose Open.
8. Choose Add.
9. Copy API endpoint for later use.

Preparing the lambda layer

This code uses external modules: requests and boto3. boto3 is already supported by lambda runtime. When creating a lambda function in AWS that requires external modules, one of the options is to use a lambda layer that contains all these modules. That way, the lambda is independent of those modules, can be updated by itself, and also you can share that layer between lambdas that use the same modules, thus making it easier to maintain.

Layer with requests is included as lambda-layer.zip. However, in case more external modules are needed, you can follow instruction below.

Create lambda layer (optional)

Before starting, make sure you're using python3.8 since lambda runtime is python3.8. First create a folder structure for the modules that need to be installed.

mkdir -p lambda-layer/python/lib/python3.8/site-packages

Once the folder is created we can install requests and any other module in that folder.

pip3 install requests --target lambda-layer/python/lib/python3.8/site-packages

That folder structure is important because that is where Python expects to find the modules.

Now we can go into the lambda-layer folder and create a zip file for the layer that will be uploaded using the console.

cd lambda-layer
zip -r9 lambda-layer.zip .

Creating the layer

1. Go to Services -> Lambda -> Layers and choose Create layer.
2. Name (ex: telegramBotRequestsLayer).
3. Upload lambda-layer.zip.
4. For runtime choose Python 3.8 and choose Create.

Connecting the layer to lambda

1. Go to Services -> Lambda -> Functions and select the lambda function.
2. Under Layers choose Add a layer.
3. Choose Custom layers and select the layer.
4. Press Add.

Create telegram bot

Reference: https://core.telegram.org/bots/api

1. Talk to BotFather to create a new bot and get your bot token.
2. Set webhook by sending following request with your TELEGRAM_BOT_TOKEN and LAMBDA_HTTP_API_ENDPOINT (you can use browser): https://api.telegram.org/bot{TELEGRAM_BOT_TOKEN}/setWebhook?url={LAMBDA_HTTP_API_ENDPOINT}

Setup lambda function

1. Go to Lambda -> Functions and choose the lambda function.
2. Copy and paste code from lambda_function.py code source box and deploy.
3. In Configuration -> Environment variables set following values:

• ADMIN_CHAT_ID: admin's chat id (you can find this by texting the bot and printing the event)
• TELEGRAM_BOT_TOKEN: bot token you got fron BotFather
• CURRENCY_A: name of currency A in english (e.g. tenge)
• CURRENCY_A_RUS: name of currency A in russian (e.g. тенге)
• CURRENCY_B: name of currency B in english (e.g. euro)
• CURRENCY_B_RUS: name of currency B in russian (e.g. евро)

4. In Configuration -> General configuration set memory to 256MB and timeout to 30secs.

Setup DynamoDB

Go to DynamoDB and create following tables:

1. name: {CURRENCY_A}2{CURRENCY_B} (e.g. tenge2euro); partition key name: user_id, type: number; no sort key
2. name: {CURRENCY_B}2{CURRENCY_A} (e.g. euro2tenge); partition key name: user_id, type: number; no sort key
3. name: {CURRENCY_A}2{CURRENCY_B}_telegram_hist (e.g. tenge2euro_telegram_hist); partition key name: user_id, type: number; sort key name: date, type: number
4. name: {CURRENCY_A}2{CURRENCY_B}_transaction_history (e.g. tenge2euro_transaction_history); partition key name: date, type: number; no sort key

Configure IAM Role for lambda

Lambda need to access DynamoDB.

1. Go to IAM -> Roles.
2. Choose default role used by the lambda.
3. Choose Add inline policy.
4. For service choose DynamoDB.
5. Actions: PutItem, DeleteItem, GetItem, Scan, Query.
6. Resources: All resources.
7. Choose Review policy.
8. Set name to DynamoDBReadWrite.

How to run tests

Install pipenv

python3 -m pip install pipenv

Install from Pipfile

python3 -m pipenv install

Activate environment and run tests

python3 -m pipenv shell
python -m unittest test_lambda_function.py