---
title: AWS Lambda for Beginners | Codurance
description: Our team of dedicated software craftspeople provides consultancy, software development, and training services to clients seeking high quality development processes and software solutions.
---

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# [AWS Lambda for Beginners | Codurance](https://www.codurance.com/publications/2016/05/11/aws-lambdas)

 Written by [Mashooq Badar](https://www.codurance.com/publications/author/mashooq-badar) | 10 May 2016

AWS Lambda is a compute service from Amazon. It makes deployment and provisioning very simple and fits very well with microservices based architecture. You can find out more about AWS Lambda [here](http://docs.aws.amazon.com/lambda/latest/dg/welcome.html). Currently supported platforms are JVM, Node JS and Python.

The programming model for the lambdas consists of **Handler, Context Object, Logging and Exceptions**. These are described [here](http://docs.aws.amazon.com/lambda/latest/dg/programming-model-v2.html). Lambda must not hold state because they are brought up and down and replicated as needed. Persistent state should be stored in a service that is outside the lifecycle of the lambda such as Amazon DynamoDB, S3 etc.

First of all follow the instructions [here](http://docs.aws.amazon.com/lambda/latest/dg/setup.html) to setup an AWS Account and AWS Command-line Interface and note down your account id. You'll need to add billing information to your account even though this exercise will not incur charges.

### Step 1: The Code

The most basic lambda will look like the following in Python:

```
def lambda_handler(event, context):
  return "Hello World!"
```

or like the following in Java:

```
package example;

import com.amazonaws.services.lambda.runtime.Context; 

public class Hello {
    public String lambdaHandler(String event, Context context) {
        return "Hello World!";
    }
}
```

You can follow the, somewhat lengthy, instructions [here](http://docs.aws.amazon.com/lambda/latest/dg/get-started-create-function.html) to deploy this function … but that’s no fun! Let’s do it devops style ;)

Paste the above Python code in a file called `helloworld.py`. If you want to use the Java version then follow the instructions [here](http://docs.aws.amazon.com/lambda/latest/dg/java-create-jar-pkg-maven-no-ide.html) to build your lambda and create a deployment package using Maven.

### Step 2: The Role

Create a `trust.json` file . The trust allows our function to assume the [role](http://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles.html) of an AWS Lambda.

In `trust.json` we are allowing the function to assume the role of a `lambda.amazonaws.com` service, otherwise the infra will not allow our function to run.

```
{
  "Version": "2012-10-17",
  "Statement": [{
    "Sid": "",
    "Effect": "Allow",
    "Principal": {
      "Service": "lambda.amazonaws.com"
    },
    "Action": "sts:AssumeRole"
  }]
}
```

### Step 3: The Deployment

Create the following script (`deploy.sh`). *Note: the script assumes that you have the `AWS_ACCOUNT_ID` environment variable set.*

```
#!/bin/bash
 ### Ensure the variable AWS_ACCOUNT_ID is set
# http://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash
if [ -z ${AWS_ACCOUNT_ID+x} ]; then
    echo "variable AWS_ACCOUNT_ID is not set"
    exit 1
fi
 ### Create the lambda package
zip -j helloworld.zip *.py
 ### Create the role for the lambda to assume
role="helloworld_exec_role"
trust="trust.json"
aws iam create-role --role-name $role --assume-role-policy-document file://$trust
aws iam update-assume-role-policy --role-name $role --policy-document file://$trust
 ### Create the lambda function
function_name="helloworld"
handler_name="helloworld.lambda_handler"
package_file=helloworld.zip
runtime=python2.7
aws lambda create-function \
  --function-name $function_name \
  --handler $handler_name \
  --runtime $runtime \
  --memory 512 \
  --timeout 60 \
  --role arn:aws:iam::${AWS_ACCOUNT_ID}:role/$role \
  --zip-file fileb://$package_file
```

or for Java:

```
#!/bin/bash
 ### Ensure the variable AWS_ACCOUNT_ID is set
# http://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash
if [ -z ${AWS_ACCOUNT_ID+x} ]; then
    echo "variable AWS_ACCOUNT_ID is not set"
    exit 1
fi
 ### Create the lambda package
mvn package
 ### Create the role for the lambda to assume
role="helloworld_exec_role"
trust="trust.json"
aws iam create-role --role-name $role --assume-role-policy-document file://$trust
aws iam update-assume-role-policy --role-name $role --policy-document file://$trust
 ### Create the lambda function
function_name="helloworld"
handler_name="example.Hello::lambdaHandler"
package_file="target/lambda-java-example-1.0-SNAPSHOT.jar"
runtime="java8"
aws lambda create-function \
  --function-name $function_name \
  --handler $handler_name \
  --runtime $runtime \
  --memory 512 \
  --timeout 60 \
  --role arn:aws:iam::${AWS_ACCOUNT_ID}:role/$role \
  --zip-file fileb://${package_file}
```

Make the script executable `chmod +x deploy.sh` and deploy your lambda `./deploy.sh`. You may get the following error: "The role defined for the function cannot be assumed by Lambda." This is because the role has not been replicated through in the Amazon infra. Just run the deploy script again. It will complain that the role already exists but this time the lambda creation should pass. In the future we will look at a status check to make sure that the role has been fully created before we deploy the function.

### Step 4: The Execution!

Invoke your lambda with the below command. You should see the result in the file called `output.txt`

```
aws lambda invoke --invocation-type RequestResponse --function-name helloworld --payload '[""]' output.txt
```

### Step 5: The Cleanup

To delete the lambda function and then the role paste the following in `delete.sh`

```
#!/bin/bash
role="helloworld_exec_role"
function_name="helloworld"
aws lambda delete-function --function-name $function_name
aws iam delete-role --role-name $role
```

Then make the script executable `chmod +x delete.sh` and execute `./delete.sh`

### Step 6: Relax ... you have arrived ;)

... and wait for the next post on AWS frolics

[View full post](https://www.codurance.com/publications/2016/05/11/aws-lambdas)

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