Problems accessing storage from Lambda function in Amplify - amazon-web-services

Question

What I want to do?
I want to create REST API that returns data from my DynamoDB table which is being created by GraphQL model.
What I've done
Create GraphQL model
type Public #model {
id: ID!
name: String!
}
Create REST API with Lambda Function with access to my PublicTable
$ amplify add api
? Please select from one of the below mentioned services: REST
? Provide a friendly name for your resource to be used as a label for this category in the project: rest
? Provide a path (e.g., /book/{isbn}): /items
? Choose a Lambda source Create a new Lambda function
? Provide an AWS Lambda function name: listPublic
? Choose the runtime that you want to use: NodeJS
? Choose the function template that you want to use: Hello World
Available advanced settings:
- Resource access permissions
- Scheduled recurring invocation
- Lambda layers configuration
? Do you want to configure advanced settings? Yes
? Do you want to access other resources in this project from your Lambda function? Yes
? Select the category storage
? Storage has 8 resources in this project. Select the one you would like your Lambda to access Public:#model(appsync)
? Select the operations you want to permit for Public:#model(appsync) create, read, update, delete
You can access the following resource attributes as environment variables from your Lambda function
API_MYPROJECT_GRAPHQLAPIIDOUTPUT
API_MYPROJECT_PUBLICTABLE_ARN
API_MYPROJECT_PUBLICTABLE_NAME
ENV
REGION
? Do you want to invoke this function on a recurring schedule? No
? Do you want to configure Lambda layers for this function? No
? Do you want to edit the local lambda function now? No
Successfully added resource listPublic locally.
Next steps:
Check out sample function code generated in <project-dir>/amplify/backend/function/listPublic/src
"amplify function build" builds all of your functions currently in the project
"amplify mock function <functionName>" runs your function locally
"amplify push" builds all of your local backend resources and provisions them in the cloud
"amplify publish" builds all of your local backend and front-end resources (if you added hosting category) and provisions them in the cloud
Succesfully added the Lambda function locally
? Restrict API access No
? Do you want to add another path? No
Successfully added resource rest locally
Edit my Lambda function
/* Amplify Params - DO NOT EDIT
API_MYPROJECT_GRAPHQLAPIIDOUTPUT
API_MYPROJECT_PUBLICTABLE_ARN
API_MYPROJECT_PUBLICTABLE_NAME
ENV
REGION
Amplify Params - DO NOT EDIT */
const AWS = require("aws-sdk");
const region = process.env.REGION
AWS.config.update({ region });
const docClient = new AWS.DynamoDB.DocumentClient();
const params = {
TableName: "PublicTable"
}
async function listItems(){
try {
const data = await docClient.scan(params).promise()
return data
} catch (err) {
return err
}
}
exports.handler = async (event) => {
try {
const data = await listItems()
return { body: JSON.stringify(data) }
} catch (err) {
return { error: err }
}
};
Push my updates
$ amplify push
Open my REST API endpoint /items
{
"message": "User: arn:aws:sts::829736458236:assumed-role/myprojectLambdaRolef4f571b-dev/listPublic-dev is not authorized to perform: dynamodb:Scan on resource: arn:aws:dynamodb:us-east-1:8297345848236:table/Public-ssrh52tnjvcdrp5h7evy3zdldsd-dev",
"code": "AccessDeniedException",
"time": "2021-04-21T21:21:32.778Z",
"requestId": "JOA5KO3GVS3QG7RQ2V824NGFVV4KQNSO5AEMVJF66Q9ASUAAJG",
"statusCode": 400,
"retryable": false,
"retryDelay": 28.689093010346657
}
Problems
What I did wrong?
How do I access my table and why I didn't get it when I created it?
Why API_MYPROJECT_PUBLICTABLE_NAME and other constants are needed?

Answer 1

Decision
The problem turned out to be either the NodeJS version or the amplify-cli version. After updating amplify-cli and installing the node on the 14.16.0 version, everything worked.
I also changed the name of the table to what Amplify creates for us, although this code did not work before. The code became like this:
/* Amplify Params - DO NOT EDIT
API_MYPROJECT_GRAPHQLAPIIDOUTPUT
API_MYPROJECT_PUBLICTABLE_ARN
API_MYPROJECT_PUBLICTABLE_NAME
ENV
REGION
Amplify Params - DO NOT EDIT */
const AWS = require("aws-sdk");
const region = process.env.REGION
const tableName = process.env.API_MYPROJECT_PUBLICTABLE_NAME
AWS.config.update({ region });
const docClient = new AWS.DynamoDB.DocumentClient();
const params = {
TableName: tableName
}
async function listItems(){
try {
const data = await docClient.scan(params).promise()
return data
} catch (err) {
return err
}
}
exports.handler = async (event) => {
try {
const data = await listItems()
return { body: JSON.stringify(data) }
} catch (err) {
return { error: err }
}
};