Python AWS function failing to return ELB data through Lambda - works on console

Question

This should be simple so I'm hoping some can help with this quite quickly.

I have the following basic python script:

import boto3
elb = boto3.client('elb')
print(elb.describe_load_balancers())

When I execute this via a python script on the command line it works perfectly, returning all information for all load balancers.

The CLI command also works perfectly from the command line:

aws elb describe-load-balancers

However when I add the script into AWS's Lambda function it fails. This is how the script looks in AWS lambda:

import boto3

def lambda_handler(event, context):
    elb = boto3.client('elb')
    return elb.describe_load_balancers()

Which should work like the others returning all the load balancers data, however it returns this error:

{
  "stackTrace": [
    [
      "/usr/lib64/python2.7/json/__init__.py",
      250,
      "dumps",
      "sort_keys=sort_keys, **kw).encode(obj)"
    ],
    [
      "/usr/lib64/python2.7/json/encoder.py",
      207,
      "encode",
      "chunks = self.iterencode(o, _one_shot=True)"
    ],
    [
      "/usr/lib64/python2.7/json/encoder.py",
      270,
      "iterencode",
      "return _iterencode(o, 0)"
    ],
    [
      "/var/runtime/awslambda/bootstrap.py",
      41,
      "decimal_serializer",
      "raise TypeError(repr(o) + \" is not JSON serializable\")"
    ]
  ],
  "errorType": "TypeError",
  "errorMessage": "datetime.datetime(2013, 7, 26, 15, 35, 57, 690000, tzinfo=tzlocal()) is not JSON serializable"
}

I have been pulling my hair out all day with this so far and can't work out what is wrong, so any help would be appreciated.

As an extra note I was able to get this function working in AWS lambda just fine:

import boto3

def lambda_handler(event, context):
    elb = boto3.client('elb')
    return elb.describe_tags(LoadBalancerNames=[event['loadBalancer']])

As you may notice in the above command I have specifed the load balancer instead of all of them, I have tried this with the other function too but with no luck.

Answer 1

I was digging same references with Jim.P's and trying on my account. this answer gave me the correct result with proper implementation:

import boto3
import json
import datetime
from time import mktime

class MyEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, datetime.datetime):
            return int(mktime(obj.timetuple()))
        return json.JSONEncoder.default(self, obj)

def lambda_handler(event, context):
    elb = boto3.client('elb')
    return json.dumps(elb.describe_load_balancers(), cls = MyEncoder)

Answer 2

This looks like it may be "python" specific, and the reason it probably works on your local machine is you have a python library that is not included in your lambda function.

Several articles describing your error:

StackOverflow - 455580

StackOverflow - 11875770

And documentation on creating a deployment package for Lambda Python:

Creating a Deployment Package (Python)