How to configure dynamodb-to-lambda trigger using amplify framework/cli

The amplify docks here says that we can configure a lambda function as a dynamodb trigger by running **amplify add function** and selecting the "Lambda Trigger" option, but when I run the "amplify add api" (selected Python as runtime language) I am not getting the lambda trigger option, I'm only getting the "Serverless function" and "lambda layer" options.

Please help me to resolve this issue to access the feature.

docs snapshot - showing 4 options

my CLI snapshot - showing only 2 options

I know it works for nodejs runtime lambda, but I want this option for Python Lambda as well.

Upvotes: 4

Answers (4)

maydna

Reputation: 1

just add the following to {YOUR_FUNCTION_NAME}-cloudformation-template.json, remember to replace (YOUR_TABLE_NAME) to your table name.

"LambdaTriggerPolicyPurchase": {
  "DependsOn": [
    "LambdaExecutionRole"
  ],
  "Type": "AWS::IAM::Policy",
  "Properties": {
    "PolicyName": "amplify-lambda-execution-policy-Purchase",
    "Roles": [
      {
        "Ref": "LambdaExecutionRole"
      }
    ],
    "PolicyDocument": {
      "Version": "2012-10-17",
      "Statement": [
        {
          "Effect": "Allow",
          "Action": [
            "dynamodb:DescribeStream",
            "dynamodb:GetRecords",
            "dynamodb:GetShardIterator",
            "dynamodb:ListStreams"
          ],
          "Resource": {
            "Fn::ImportValue": {
              "Fn::Sub": "${apilanguageGraphQLAPIIdOutput}:GetAtt:(YOUR_TABLE_NAME):StreamArn"
            }
          }
        }
      ]
    }
  }
},
"LambdaEventSourceMappingPurchase": {
  "Type": "AWS::Lambda::EventSourceMapping",
  "DependsOn": [
    "LambdaTriggerPolicyPurchase",
    "LambdaExecutionRole"
  ],
  "Properties": {
    "BatchSize": 100,
    "Enabled": true,
    "EventSourceArn": {
      "Fn::ImportValue": {
        "Fn::Sub": "${apilanguageGraphQLAPIIdOutput}:GetAtt:(YOUR_TABLE_NAME):StreamArn"
      }
    },
    "FunctionName": {
      "Fn::GetAtt": [
        "LambdaFunction",
        "Arn"
      ]
    },
    "StartingPosition": "LATEST"
  }
},

i got them by creating a dummy function using the template that shows up after you choose nodejs and checking compare its -cloudformation-template.json with my own function

Upvotes: 0

Sam Jett

Reputation: 831

Just followed these steps with amplify CLI version 4.50.2.

To create a lambda function that is triggered by changes to a DynamoDB table, you can use the following command line actions, which are walked-through inside of the CLI after entering the below command:

amplify add function

Select which capability you want to add:

❯ Lambda function (serverless function)

Provide an AWS Lambda function name:

<YourFunctionsName>

Choose the runtime that you want to use:

> NodeJS # IMPORTANT: Must be NodeJS as of now, you can change this later by manually editing ...-cloudformation-template.json file inside function directory

Choose the function template you want to use

> Lambda Trigger

What event source do you want to associate with the lambda trigger

> Amazon DynamoDB Stream

Choose a DynamoDB event source option

>Use API category graphql @model backend DynamoDB table(s) in the current Amplify project

Choose the graphql @model(s)

<Select any models (using spacebar) you want to trigger the function after editing>

Do you want to trigger advanced settings

Y # IMPORTANT: If you are using a dynamodb event source based on a table defined by graphql schema, you will need to give this function read access to the api resource that contains the graphql schema that defines the table that drives the event

Do you want to access other resources in this project from your Lambda function?

y # See above, select your api that contains the data model and make sure that the function has at least read access.

After this, the other options (layer, call scheduling) are up to you.

After creating the function via the above CLI options, you can change the "Runtime" field inside the -cloudformation-template.json file inside function directory, eg if you want a python lambda function change the runtime to "python3.8". You will also need to create a file called index.py inside your function's directory which has a handler(event, context) function. See example below:

import json

def handler(event, context):
    print("Triggered via DynamoDB")
    print(event)
    return json.dumps({'status_code': 200, "message": "Received from DynamoDB"})

After making these edits, you can run amplify push and, if you open your fxn in the management console online, it should show an attached dynamoDB stream.

Upvotes: 5