Part of my lambda function executes twice - aws-lambda

Question

I'm writing AWS lambda function that should update daily statistics of a player each time when (s)he performs a drill. Function is being triggered once, with 0 retries configured, on new DynamoDB row event.
I'm testing the function alone, I'm certain I create only one row in DynamoDB that triggers lambda execution. Now to the funny part. My lambda is executed once as a whole, but some part of it is executed twice within the same request.
Here's the lambda code:
const AWS = require('aws-sdk');
var docClient = new AWS.DynamoDB.DocumentClient({region: 'us-west-2'});
const dailyStatsTableName = 'xxx';
const weeklyStatsTableName = 'yyy';
const monthlyStatsPlayerTableName = 'zzz';
const requestsTableName = 'qqq';
exports.handler = async (event, context, callback) => {
//Ensure idempotency of lambda as a whole
let requestID = context.awsRequestId;
let requestAlreadyProcessed = false;
await getRequest(requestsTableName, requestID, (err, data) => {
if (err) {
console.log(err);
} else {
if (data.Item) {
requestAlreadyProcessed = true;
}
}
});
if (requestAlreadyProcessed) {
console.log("This request has already been processed. Aborting.");
return;
}
console.log("Processing new assigned drill performance event. RequestID: " + requestID);
console.log(event);
const record = event.Records[0].dynamodb;
console.log(record);
if (!record || !record.NewImage) {
console.log("New record image undefined");
return;
}
console.log(record.NewImage);
//Get performed touches to count them in statistics
let touches = 0;
try {
touches = parseInt(record.NewImage.touches.N, 10);
} catch (error) {
console.error(error);
}
//Unpack date from record.NewImage.createdAt string
let performanceDate = new Date(Date.parse(record.NewImage.createdAt.S));
console.log("CreatedAt date: " + performanceDate);
//Get daily statistics object from table - I want to update if already exist
let dailyStats = {
drillID: record.NewImage.drillID.S,
targetUserID: record.NewImage.targetUserID.S,
performDay: performanceDate.getDate(),
performMonth: performanceDate.getMonth(),
performYear: performanceDate.getFullYear(),
performDate: performanceDate.toISOString(),
touches: 0,
id: undefined
};
let result = await getDailyStats(dailyStatsTableName, dailyStats.performDay, dailyStats.performMonth, dailyStats.performYear, dailyStats.drillID, dailyStats.targetUserID, (err, data) => {
if (err) {
console.log(err);
} else {
if (data.Items.length !== 0) {
console.log("Found daily stats object"); //this console.log is logged twice. Everything below that line is executed twice.
dailyStats = data.Items[0];
}
}
return "success";
});
//Create or update daily statistics
if (!dailyStats.id) {
console.log("DailyStats ID not found. Creating new with touches " + touches);
dailyStats.touches = touches;
result = await createDailyStats(dailyStatsTableName, dailyStats, requestID, (err, data) => {
if (err) {
console.log(err);
} else {
console.log("Success creating daily stats " + dailyStats.drillID + " " + dailyStats.targetUserID + " " + dailyStats.touches);
}
return "success";
});
} else {
console.log("DailyStats ID found. Updating existing with touches " + touches);
result = await updateDailyStats(dailyStatsTableName, dailyStats.id, touches, requestID, (err, data) => {
if (err) {
console.log(err);
} else {
console.log("Success updating daily stats " + dailyStats.drillID + " " + dailyStats.targetUserID + " " + touches);
}
return "success";
});
}
//Mark this request as processed to ensure idempotency of lambda as a whole
result = await createProcessedRequest(requestsTableName, requestID, (err, data) => {
if (err) {
console.log(err);
} else {
console.log("Success creating processed request " + requestID);
}
return "success";
});
return "success";
};
function createDailyStats(tableName, stats, requestID, callback) {
let now = new Date();
let dateTimeString = now.toISOString();
let params = {
TableName:tableName,
Item:{
"__typename": "PersonalDrillDailyStatistic",
"createdAt": dateTimeString,
"updatedAt": dateTimeString,
"id": stats.id ? stats.id : createUUID(),
"drillID": stats.drillID,
"targetUserID": stats.targetUserID,
"touches": stats.touches,
"performDay": stats.performDay,
"performMonth": stats.performMonth,
"performYear": stats.performYear,
"lastRequestID": requestID
}
};
console.log("Adding a new daily stats (with id) item... " + stats.drillID + " " + stats.targetUserID + " " + stats.touches);
return docClient.put(params, callback).promise();
}
function updateDailyStats(tableName, statsID, touches, requestID, callback) {
var params = {
TableName:tableName,
Key:{
"id": statsID
},
UpdateExpression: "set touches = touches + :val, lastRequestID = :reqID",
ExpressionAttributeValues:{
":val": touches,
":reqID": requestID
},
ConditionExpression: "lastRequestID <> :reqID", //conditional check exception is being thrown during second call, hence Exception in logs output
ReturnValues:"UPDATED_NEW"
};
console.log("Updating daily stats (with id) item... " + statsID + " " + touches);
return docClient.update(params, callback).promise();
}
function getDailyStats(tableName, performDay, performMonth, performYear, drillID, targetUserID, callback) {
console.log("Querying for daily statistics |" + performDay + "." + performMonth + "." + performYear + "| userID: |" + targetUserID + "| drillID: |" + drillID + "| from table " + tableName);
let params = {
TableName: tableName,
FilterExpression: "drillID = :drill_id and targetUserID = :user_id and performDay = :day and performMonth = :month and performYear = :year",
ExpressionAttributeValues: {
":drill_id": drillID,
":user_id": targetUserID,
":day": performDay,
":month": performMonth,
":year": performYear,
}
};
return docClient.scan(params, callback).promise();
}
function createUUID(){
(...)
}
function getRequest(tableName, requestID, callback) {
let params = {
TableName: tableName,
Key: {
"id": requestID
}
};
return docClient.get(params, callback).promise();
}
function createProcessedRequest(tableName, requestID, callback) {
let params = {
TableName:tableName,
Item:{
"id": requestID,
"name": requestID
}
};
return docClient.put(params, callback).promise();
}
Here's CloudWatch output for this lambda execution:
2021-04-16T22:24:49.754+02:00 START RequestId: 8766c005-c1f3-42fb-aee9-9e8352da67ed Version: $LATEST
2021-04-16T22:24:50.464+02:00 2021-04-16T20:24:50.464Z 8766c005-c1f3-42fb-aee9-9e8352da67ed INFO Processing new assigned drill performance event. RequestID: 8766c005-c1f3-42fb-aee9-9e8352da67ed
2021-04-16T22:24:50.523+02:00 2021-04-16T20:24:50.523Z 8766c005-c1f3-42fb-aee9-9e8352da67ed INFO { Records: [ { eventID: 'e09a400894c178ef66840f54e71b6c26', eventName: 'INSERT', eventVersion: '1.1', eventSource: 'aws:dynamodb', awsRegion: 'us-west-2', dynamodb: [Object], eventSourceARN: 'arn:aws:dynamodb:us-west-2:900776852541:table/FDrillPerformance-y22t7izqyvb2xiruvbf4zhadvm-fissiondev/stream/2021-04-15T21:48:06.158' } ] }
2021-04-16T22:24:50.541+02:00 2021-04-16T20:24:50.541Z 8766c005-c1f3-42fb-aee9-9e8352da67ed INFO { ApproximateCreationDateTime: 1618604689, Keys: { id: { S: '7321fcf5-fed2-402a-b1cf-7667e958f73a' } }, NewImage: { createdAt: { S: '2021-04-16T20:24:49.077Z' }, touches: { N: '25' }, __typename: { S: 'FDrillPerformance' }, drillID: { S: '01adc7e6-67be-4bdf-828b-36833cbd7070' }, targetUserID: { S: 'd4a95710-c4fb-4f0f-8355-76082e41c43a' }, id: { S: '7321fcf5-fed2-402a-b1cf-7667e958f73a' }, updatedAt: { S: '2021-04-16T20:24:49.077Z' } }, SequenceNumber: '218143500000000009280556527', SizeBytes: 269, StreamViewType: 'NEW_IMAGE' }
2021-04-16T22:24:50.561+02:00 2021-04-16T20:24:50.561Z 8766c005-c1f3-42fb-aee9-9e8352da67ed INFO { createdAt: { S: '2021-04-16T20:24:49.077Z' }, touches: { N: '25' }, __typename: { S: 'FDrillPerformance' }, drillID: { S: '01adc7e6-67be-4bdf-828b-36833cbd7070' }, targetUserID: { S: 'd4a95710-c4fb-4f0f-8355-76082e41c43a' }, id: { S: '7321fcf5-fed2-402a-b1cf-7667e958f73a' }, updatedAt: { S: '2021-04-16T20:24:49.077Z' } }
2021-04-16T22:24:50.581+02:00 2021-04-16T20:24:50.581Z 8766c005-c1f3-42fb-aee9-9e8352da67ed INFO CreatedAt date: Fri Apr 16 2021 20:24:49 GMT+0000 (Coordinated Universal Time)
2021-04-16T22:24:50.581+02:00 2021-04-16T20:24:50.581Z 8766c005-c1f3-42fb-aee9-9e8352da67ed INFO Querying for daily statistics |16.3.2021| userID: |d4a95710-c4fb-4f0f-8355-76082e41c43a| drillID: |01adc7e6-67be-4bdf-828b-36833cbd7070| from table PersonalDrillDailyStatistic-y22t7izqyvb2xiruvbf4zhadvm-fissiondev
2021-04-16T22:24:50.784+02:00 2021-04-16T20:24:50.783Z 8766c005-c1f3-42fb-aee9-9e8352da67ed INFO Found daily stats object
2021-04-16T22:24:50.784+02:00 2021-04-16T20:24:50.784Z 8766c005-c1f3-42fb-aee9-9e8352da67ed INFO DailyStats ID found. Updating existing with touches 25
2021-04-16T22:24:50.784+02:00 2021-04-16T20:24:50.784Z 8766c005-c1f3-42fb-aee9-9e8352da67ed INFO Updating daily stats (with id) item... ab00afe1-ed4b-4895-b1bb-31ac570fe46d 25
2021-04-16T22:24:50.883+02:00 2021-04-16T20:24:50.883Z 8766c005-c1f3-42fb-aee9-9e8352da67ed INFO Found daily stats object
2021-04-16T22:24:51.302+02:00 2021-04-16T20:24:51.302Z 8766c005-c1f3-42fb-aee9-9e8352da67ed INFO Success updating daily stats 01adc7e6-67be-4bdf-828b-36833cbd7070 d4a95710-c4fb-4f0f-8355-76082e41c43a 25
2021-04-16T22:24:51.401+02:00 2021-04-16T20:24:51.384Z 8766c005-c1f3-42fb-aee9-9e8352da67ed INFO ConditionalCheckFailedException: The conditional request failed at Request.extractError (/var/runtime/node_modules/aws-sdk/lib/protocol/json.js:52:27) at Request.callListeners (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:106:20) at Request.emit (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:78:10) at Request.emit (/var/runtime/node_modules/aws-sdk/lib/request.js:688:14) at Request.transition (/var/runtime/node_modules/aws-sdk/lib/request.js:22:10) at AcceptorStateMachine.runTo (/var/runtime/node_modules/aws-sdk/lib/state_machine.js:14:12) at /var/runtime/node_modules/aws-sdk/lib/state_machine.js:26:10 at Request.<anonymous> (/var/runtime/node_modules/aws-sdk/lib/request.js:38:9) at Request.<anonymous> (/var/runtime/node_modules/aws-sdk/lib/request.js:690:12) at Request.callListeners (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:116:18) { code: 'ConditionalCheckFailedException', time: 2021-04-16T20:24:51.383Z, requestId: 'H8PC553OQABGJKR9KFIJMR1EHJVV4KQNSO5AEMVJF66Q9ASUAAJG', statusCode: 400, retryable: false, retryDelay: 36.82252581429517 }
2021-04-16T22:24:51.462+02:00 2021-04-16T20:24:51.462Z 8766c005-c1f3-42fb-aee9-9e8352da67ed INFO Success creating processed request 8766c005-c1f3-42fb-aee9-9e8352da67ed
2021-04-16T22:24:51.482+02:00 END RequestId: 8766c005-c1f3-42fb-aee9-9e8352da67ed
2021-04-16T22:24:51.482+02:00 REPORT RequestId: 8766c005-c1f3-42fb-aee9-9e8352da67ed Duration: 1728.11 ms Billed Duration: 1729 ms Memory Size: 128 MB Max Memory Used: 91 MB Init Duration: 413.89 ms
So, you can see that even though lambda is called once, some parts of it are called twice, and I don't know how to deal with it. I need to update weekly and monthly statistics as well, so the problem will get more complicated. Hack with ConditionExpression on last request ID works, but I'd ensure that code inside my function is not invoked twice rather than try to do such workarounds.

Answer 1

Following comment of #Jason Wadsworth, I changed all function invocations in exports.handler function by removing callback functions. Please note that I left callback parameters in dynamo related functions like updateDailyStats - without it, for some reason code didn't write to database.