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access s3 objects with ALB using lambda
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import os | |
import json | |
import boto3 | |
from botocore.exceptions import ClientError | |
def lambda_handler(event, context): | |
# use 'AWS_REGION' environment variable from lambda built-in variables | |
aws_region = os.environ['AWS_REGION'] | |
bucket_name = os.environ['BUCKET_NAME'] | |
path = event['path'].split('/') | |
file_path = '/'.join(path[2:]) | |
output = { | |
"isBase64Encoded": False, | |
"statusCode": 200, | |
"statusDescription": "200 OK", | |
"headers": { | |
"Content-Type": 'text/html' | |
}, | |
} | |
if event['headers']['user-agent'] == 'ELB-HealthChecker/2.0': | |
output['body'] = 'Response to HealthCheck' | |
return output | |
s3 = boto3.resource('s3', region_name=aws_region) | |
obj = s3.Object(bucket_name, file_path) | |
try: | |
# Lambda output is limited to 1Mb when invoked from ALB. | |
object_size = obj.get()['ContentLength'] | |
object_size_in_mb = '{:.2f}'.format(object_size / 1024 / 1024) | |
if obj.get()['ContentLength'] >= 1000000: | |
output['body'] = json.dumps({'status': 'error', 'message': f'object size is {object_size_in_mb}Mb, lambda with alb is limited to 1Mb'}, indent=4) | |
return output | |
metadata = obj.get()['ResponseMetadata']['HTTPHeaders'] | |
# Extract s3 mimetype (http headers) | |
output['headers']['Content_Language'] = metadata.get('content-language') | |
output['headers']['Cache_Control'] = metadata.get('cache-control') | |
output['headers']['Content_Disposition'] = metadata.get('content-disposition') | |
output['headers']['Content_Encoding'] = metadata.get('content-encoding') | |
output['headers']['Content_Language'] = metadata.get('content-language') | |
output['headers']['Content-Type'] = metadata['content-type'] | |
# Remove empty headers to avoid 502 errors from ALB. | |
output['headers'] = {k: v for k, v in output['headers'].items() if v is not None} | |
output['body'] = obj.get()['Body'].read().encode('latin-1') | |
except ClientError as e: | |
output['body'] = json.dumps({'status': 'error', 'message': [str(e)]}, indent=4) | |
except Exception as e: | |
output['body'] = json.dumps({'status': 'unknown exception', 'message': [str(e)]}, indent=4) | |
return output |
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