Error in Lambda Passing SQL to RDS Data API

Question

In following a tutorial, I am trying to set up an AWS Lambda function that will pass a SQL query to an AWS RDS Aurora Serverless MySQL database using the Data API and return the query results (presumably as a JSON).

The code I used is below (where the params are stored as environment variables):

const AWS = require('aws-sdk')
const RDS = new AWS.RDSDataService()

exports.handler = async (event, context) => {
    console.log(JSON.stringify(event, null, 2))  // Log the entire event passed in

    // Get the sqlStatement string value
    // TODO: Implement a more secure way (e.g. "escaping") the string to avoid SQL injection
    var sqlStatement = event.sqlStatement;

    // The Lambda environment variables for the Aurora Cluster Arn, Database Name, and the AWS Secrets Arn hosting the master credentials of the serverless db
    var DBSecretsStoreArn = process.env.DBSecretsStoreArn;
    var DBAuroraClusterArn = process.env.DBAuroraClusterArn;
    var DatabaseName = process.env.DatabaseName;

    const params = {
      awsSecretStoreArn: DBSecretsStoreArn,
      dbClusterOrInstanceArn: DBAuroraClusterArn,
      sqlStatements: sqlStatement,
      database: DatabaseName
    }

    try {
      let dbResponse = await RDS.executeSql(params)
      console.log(JSON.stringify(dbResponse, null, 2))

      return JSON.stringify(dbResponse)

    } catch (error) {
        console.log(error)
      return error
    }
}

I run the following test from the Lambda console (where "Bonds" is the name of an existing table in my database):

{
    "sqlStatement": "SELECT * FROM Bonds"
}

My test is logged as a success, with a blank output {} and the following error information logged:

INFO    TypeError: Converting circular structure to JSON
    --> starting at object with constructor 'Request'
    |     property 'response' -> object with constructor 'Response'
    --- property 'request' closes the circle
    at JSON.stringify (<anonymous>)
    at Runtime.exports.handler (/var/task/index.js:25:24)END

Does anyone know how I can successfully retrieve data with this method, and/or what the above error means?

You can't convert circular object to string using JSON.stringify, to check response you can console directly the dbResponse — Vibha Chosla
– Vibha Chosla, Commented Nov 27, 2019 at 8:14
You can check on stackoverflow.com/questions/11616630/… for reference to convert into json string — Vibha Chosla
– Vibha Chosla, Commented Nov 27, 2019 at 8:18

Noel Llevares · Accepted Answer · 2019-11-28 17:50:09Z

4

RDS.executeSql(params) does not return a promise that you can await. It simply constructs a request object for you.

Replace it instead with await RDS.executeSql(params).promise() so you can get the value that you want.

References:

answered Nov 28, 2019 at 17:50

Noel Llevares

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3 Comments

OJT Over a year ago

Thank you! That seemed to do the trick (for that error) -- I now get errors related to permissions for the lambda role -- I need it to be able to perform SELECT queries on the RDS database and pass on the results as JSON -- any insight into how this might be done?

OJT Over a year ago

*SELECT queries only... no database modifications.

Noel Llevares Over a year ago

@OJT For that you will need to give your Lambda IAM permissions to use executeSql. See this page for details: docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/…

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