fn-serverless/docs/lambda/environment.md

Environment

The base images strive to provide the same environment that AWS provides to Lambda functions. This page describes it and any incompatibilities between AWS Lambda and Dockerized Lambda.

Request/Response

Functions has sync/async communication with Request/Response workflows.

• sync: returns the result as the body of the response
• async: returns the task id in the body of the response as a json

The context.succeed() will not do anything with result on node.js, nor will returning anything from a Python function.

Paths

We do not make any compatibility efforts towards running your lambda function in the same working directory as it would run on AWS. If your function makes such assumptions, please rewrite it.

nodejs

• node.js version 0.10.42
• ImageMagick version 6.9.3 and nodejs wrapper 6.9.3
• aws-sdk version 2.2.12

Event

Payloads MUST be a valid JSON object literal.

Context object

• context.fail() does not currently truncate error logs.
• context.functionName is of the form of a docker image, for example username/test-function.
• context.functionVersion is always the string "$LATEST".
• context.invokedFunctionArn is not supported. Value is empty string.
• context.memoryLimitInMB does not reflect reality. Value is always 256.
• context.awsRequestId reflects the environment variable TASK_ID. On local runs from fn tool this is a UUID. On Functions server this is the task ID.
• logGroupName and logStreamName are empty strings.
• identity and clientContext are always null.

Exceptions

If your handler throws an exception, we only log the error message. There is no v8::CallSite compatible stack trace yet.

Python 2.7

• CPython 2.7.11
• boto3 (Python AWS SDK) 1.2.3.

Event

Event is always a __dict__ and the payload MUST be a valid JSON object literal.

Context object

• context.functionName is of the form of a docker image, for example username/test-function.
• context.functionVersion is always the string "$LATEST".
• context.invokedFunctionArn is None.
• context.awsRequestId reflects the environment variable TASK_ID which is set to the task ID on Functions. If TASK_ID is empty, a new UUID is used.
• logGroupName, logStreamName, identity and clientContext are None.

Exceptions

If your Lambda function throws an Exception, it will not currently be logged as a JSON object with trace information.

Java 8

• OpenJDK Java Runtime 1.8.0

The Java8 runtime is significantly lacking at this piont and we do not recommend using it.

Handler types

There are some restrictions on the handler types supported.

Only a void return type is allowed

Since Lambda does not support request/response invocation, we explicitly prohibit a non-void return type on the handler.

JSON parse error stack differences

AWS uses the Jackson parser, this project uses the GSON parser. So JSON parse errors will have different traces.

Single item vs. List

Given a list handler like:

public static void myHandler(List<Double> l) {
    // ...
}

If the payload is a single number, AWS Lambda will succeed and pass the handler a list with a single item. This project will raise an exception.

Collections of POJOs

This project cannot currently deserialize a List or Map containing POJOs. For example:

public class Handler {
  public static MyPOJO {
    private String attribute;
    public void setAttribute(String a) {
      attribute = a;
    }

    public String getAttribute() {
      return attribute;
    }
  }

  public static void myHandler(List<MyPOJO> l) {
    // ...
  }
}

This handler invoked with the below event will fail!

[{ "attribute": "value 1"}, { "attribute": "value 2" }]

Leveraging predefined types is not supported

Using the types in aws-lambda-java-core to implement handlers is untested and unsupported right now. While the package is available in your function, we have not tried it out.

Logging

The log4j and LambdaLogger styles that log to CloudWatch are not supported.

Context object

• context.getFunctionName() returns a String of the form of a docker image, for example username/test-function.
• context.getFunctionVersion() is always the string "$LATEST".
• context.getAwsRequestId() reflects the environment variable TASK_ID which is set to the task ID on Functions. If TASK_ID is empty, a new UUID is used.
• getInvokedFunctionArn(), getLogGroupName(), getLogStreamName(), getIdentity(), getClientContext(), getLogger() return null.