mxnet error encountered in Lambda Function

Question

I trained and deployed a semantic segmentation network (mlp2.xlarge) using SageMaker. I wanted to use an AWS Lambda function to send an image to this endpoint and get a mask in return however when I use invoke_endpoint it gives an mxnet error in the logs. Funnily when I use the deployed model from a transformer object from inside the SageMaker notebook the mask is returned properly.
Here is my Lambda function code:

```
import json
import boto3

s3r = boto3.resource('s3')

def lambda_handler(event, context):
    # TODO implement
    
    bucket = event["body"]
    key = 'image.jpg'
    local_file_name = '/tmp/'+key
    s3r.Bucket(bucket).download_file(key, local_file_name)

runtime = boto3.Session().client('sagemaker-runtime')

with open('/tmp/image.jpg', 'rb') as imfile:
        imbytes = imfile.read()

# Now we use the SageMaker runtime to invoke our endpoint, sending the review we were given
    response = runtime.invoke_endpoint(
    EndpointName='semseg-2021-12-03-10-05-58-495', 
    ContentType='application/x-image', 
    Body=bytearray(imbytes))                       # The actual image

# The response is an HTTP response whose body contains the result of our inference
    result = response['Body'].read()
    
    return {
        'statusCode': 200,
        'body': json.dumps(result)
    }
```

Here are the errors I see in the logs:
mxnet.base.MXNetError: [10:26:14] /opt/brazil-pkg-cache/packages/AIAlgorithmsMXNet/AIAlgorithmsMXNet-1.4.x.4276.0/AL2_x86_64/generic-flavor/src/3rdparty/dmlc-core/src/recordio.cc:12: Check failed: size < (1 << 29U) RecordIO only accept record less than 2^29 bytes

Answer

If you are using the built-in Sagemaker algorithm for Semantic Segmentation , the content type must be "image/jpeg" for inference to accept images. For more details, see https://docs.aws.amazon.com/sagemaker/latest/dg/semantic-segmentation.html

mxnet error encountered in Lambda Function

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