AWS SDK Lambda: Invoke Functions and Write Handlers in Python, PHP and Node.js

By Ravindra Bagale, trainer · LinkedIn · Last updated: 24 October 2026

1. The big picture: a vending machine

Why do we need this?

You press a button and the vending machine wakes up, makes a coffee and goes back to sleep. You pay per coffee, not for the machine standing there. A Lambda handler is the recipe; an invoke is pressing the button; the event is the button you pressed.

What is it?

A handler receives an event (JSON) and a context (request ID, time left) and returns JSON. Invoke type RequestResponse waits for the result; Event queues it and returns 202 at once.

How to do it (step by step)

2. Write the handler in three languages

Why do we need this?

Hans sells watches in CHF; Neha shows prices in INR. One small function converts amounts for both shops.

What is it?

Python and Node.js are managed runtimes. PHP runs on Lambda with the Bref layer (provided.al2023 runtime). The input and output are the same JSON in all three.

How to do it (step by step)

1. Python handler: app.py.

# app.py
import json, os

RATES = json.loads(os.environ.get("RATES", '{"CHF_INR": 95.2, "EUR_INR": 90.1, "USD_INR": 83.9}'))

def handler(event, context):
    pair = f'{event["from"]}_{event["to"]}'
    amount = round(event["amount"] * RATES[pair], 2)
    print(f"convert {event} -> {amount} req={context.aws_request_id}")
    return {"pair": pair, "amount": amount}

Expected output:

(saved app.py)

2. Node.js handler: index.mjs.

// index.mjs
const RATES = JSON.parse(process.env.RATES ?? '{"CHF_INR":95.2,"EUR_INR":90.1,"USD_INR":83.9}');

export const handler = async (event, context) => {
  const pair = `${event.from}_${event.to}`;
  const amount = Math.round(event.amount * RATES[pair] * 100) / 100;
  console.log("convert", event, "->", amount, "req", context.awsRequestId);
  return { pair, amount };
};

Expected output:

(saved index.mjs)

3. PHP handler with Bref: index.php.

<?php
// composer require bref/bref
// index.php
require __DIR__ . "/vendor/autoload.php";

return function (array $event, $context) {
    $rates = json_decode(getenv("RATES") ?: '{"CHF_INR":95.2,"EUR_INR":90.1,"USD_INR":83.9}', true);
    $pair = $event["from"] . "_" . $event["to"];
    $amount = round($event["amount"] * $rates[$pair], 2);
    error_log("convert $pair -> $amount");
    return ["pair" => $pair, "amount" => $amount];
};

Expected output:

(saved index.php)

4. Test the Python handler locally before deploying.

python -c "import app,types;print(app.handler({'from':'CHF','to':'INR','amount':250},types.SimpleNamespace(aws_request_id='local')))"

Expected output:

convert {'from': 'CHF', 'to': 'INR', 'amount': 250} -> 23800.0 req=local
{'pair': 'CHF_INR', 'amount': 23800.0}

3. Create the function from code

Why do we need this?

Your deploy script or CI job should create or update the function, not a person clicking the console.

What is it?

CreateFunction needs a name, runtime, handler, execution role ARN and the zip bytes. UpdateFunctionCode replaces the code later. Wait for the function to be Active.

How to do it (step by step)

1. Zip the Python handler.

zip fx.zip app.py
unzip -l fx.zip | tail -1

Expected output:

      412                     1 file

2. Python: create_function and wait.

import boto3

lam = boto3.client("lambda", region_name="eu-central-2")
with open("fx.zip", "rb") as f:
    lam.create_function(
        FunctionName="fx-convert", Runtime="python3.12", Handler="app.handler",
        Role="arn:aws:iam::111122223333:role/lambda-basic-exec", Code={"ZipFile": f.read()},
        Timeout=10, MemorySize=256, Environment={"Variables": {"RATES": '{"CHF_INR": 95.2, "EUR_INR": 90.1, "USD_INR": 83.9}'}},
    )
lam.get_waiter("function_active_v2").wait(FunctionName="fx-convert")
print(lam.get_function(FunctionName="fx-convert")["Configuration"]["State"])

Expected output:

Active

3. Node.js: update the code later.

import { LambdaClient, UpdateFunctionCodeCommand, waitUntilFunctionUpdatedV2 } from "@aws-sdk/client-lambda";
import { readFileSync } from "node:fs";

const lam = new LambdaClient({ region: "eu-central-2" });
const r = await lam.send(new UpdateFunctionCodeCommand({ FunctionName: "fx-convert", ZipFile: readFileSync("fx.zip") }));
await waitUntilFunctionUpdatedV2({ client: lam, maxWaitTime: 60 }, { FunctionName: "fx-convert" });
console.log("CodeSha256:", r.CodeSha256);

Expected output:

CodeSha256: q2b3c4d5e6f7g8h9i0j1k2l3m4n5o6p7q8r9s0t1u2v=

4. Verify.

aws lambda get-function-configuration --function-name fx-convert --region eu-central-2 --query "[Runtime,State,LastUpdateStatus]" --output text

Expected output:

python3.12	Active	Successful

4. Invoke synchronously

Why do we need this?

Neha's checkout page needs the INR price right now, before it renders.

What is it?

RequestResponse returns StatusCode 200 and a Payload. If the handler throws, StatusCode is still 200 but FunctionError is set — always check it.

How to do it (step by step)

1. Python.

import boto3, json

lam = boto3.client("lambda", region_name="eu-central-2")
r = lam.invoke(FunctionName="fx-convert", Payload=json.dumps({"from": "CHF", "to": "INR", "amount": 250}))
if "FunctionError" in r:
    raise RuntimeError(r["Payload"].read())
print(r["StatusCode"], json.loads(r["Payload"].read()))

Expected output:

200 {'pair': 'CHF_INR', 'amount': 23800.0}

2. PHP.

<?php
require "vendor/autoload.php";
$lam = new Aws\Lambda\LambdaClient(["region" => "eu-central-2"]);
$r = $lam->invoke(["FunctionName" => "fx-convert", "Payload" => json_encode(["from" => "EUR", "to" => "INR", "amount" => 40])]);
if (!empty($r["FunctionError"])) { throw new RuntimeException((string) $r["Payload"]); }
echo $r["StatusCode"], " ", (string) $r["Payload"], PHP_EOL;

Expected output:

200 {"pair": "EUR_INR", "amount": 3604.0}

3. Node.js: decode the Uint8Array payload.

import { LambdaClient, InvokeCommand } from "@aws-sdk/client-lambda";

const lam = new LambdaClient({ region: "eu-central-2" });
const r = await lam.send(new InvokeCommand({ FunctionName: "fx-convert", Payload: JSON.stringify({ from: "USD", to: "INR", amount: 19.99 }) }));
if (r.FunctionError) throw new Error(new TextDecoder().decode(r.Payload));
console.log(r.StatusCode, JSON.parse(new TextDecoder().decode(r.Payload)));

Expected output:

200 { pair: 'USD_INR', amount: 1677.16 }

4. Verify: a bad pair shows FunctionError.

aws lambda invoke --function-name fx-convert --region eu-central-2 --cli-binary-format raw-in-base64-out --payload '{"from":"GBP","to":"JPY","amount":1}' out.json --query FunctionError --output text
cat out.json

Expected output:

Unhandled
{"errorMessage": "'GBP_JPY'", "errorType": "KeyError", ...}

5. Invoke asynchronously and read logs

Why do we need this?

After an order, sending a receipt can happen in the background. The customer should not wait for it.

What is it?

InvocationType Event returns 202 immediately; Lambda retries twice on errors. LogType Tail on a sync call returns the last 4 KB of logs, base64 encoded.

How to do it (step by step)

1. Python: fire and forget.

import boto3, json
lam = boto3.client("lambda", region_name="eu-central-2")
r = lam.invoke(FunctionName="fx-convert", InvocationType="Event", Payload=json.dumps({"from": "CHF", "to": "INR", "amount": 99}))
print(r["StatusCode"])

Expected output:

202

2. Node.js: tail the logs of one call.

import { LambdaClient, InvokeCommand } from "@aws-sdk/client-lambda";
const lam = new LambdaClient({ region: "eu-central-2" });
const r = await lam.send(new InvokeCommand({ FunctionName: "fx-convert", LogType: "Tail", Payload: JSON.stringify({ from: "EUR", to: "INR", amount: 10 }) }));
console.log(Buffer.from(r.LogResult, "base64").toString().split("\n").filter(l => l.startsWith("convert")));

Expected output:

[ "convert {'from': 'EUR', 'to': 'INR', 'amount': 10} -> 901.0 req=3f1c..." ]

3. PHP: async invoke.

<?php
require "vendor/autoload.php";
$lam = new Aws\Lambda\LambdaClient(["region" => "eu-central-2"]);
$r = $lam->invoke(["FunctionName" => "fx-convert", "InvocationType" => "Event", "Payload" => json_encode(["from" => "USD", "to" => "INR", "amount" => 5])]);
echo $r["StatusCode"], PHP_EOL;

Expected output:

202

4. Verify: logs show all calls.

aws logs tail /aws/lambda/fx-convert --region eu-central-2 --since 10m | grep -c convert

Expected output:

5

6. The same call in Java, Go, .NET and the CLI

Why do we need this?

Teams often mix languages. Once you know the call in Python, PHP and Node.js, the other SDKs are the same API with different syntax.

What is it?

All of them call the Invoke API. Use the CLI line to test it quickly from a terminal.

How to do it (step by step)

7. Clean up so nothing keeps costing

Why do we need this?

Lab resources left running cost money and can be a security risk.

What is it?

Delete in reverse order: children first, then parents.

How to do it (step by step)

1. Delete the function and its log group.

aws lambda delete-function --function-name fx-convert --region eu-central-2
aws logs delete-log-group --log-group-name /aws/lambda/fx-convert --region eu-central-2

Expected output:

(no output means success)

8. Interview questions and answers

Revision, comparison and interview cards

Revise this lesson in a few minutes. Save the cards on your phone or download them as PNG files. The QR code on each card opens this lesson.

More cards: Ravi Sir's Cards.