support for Application ELB target

[rejithcr]

While calling from application ELB, always getting 502 gateway error

[sidoh]

Same here with a VPC endpoint for API gateway. The error internally appears to be because headers flask-lambda is expecting are not set by the upstream:

[ERROR] KeyError: 'HTTP_X_FORWARDED_PORT'
Traceback (most recent call last):
  File "/opt/package/flask_lambda.py", line 102, in __call__
    make_environ(event),
  File "/opt/package/flask_lambda.py", line 58, in make_environ
    environ['HOST'] = '%(HTTP_HOST)s:%(HTTP_X_FORWARDED_PORT)s' % environ

[kubitz]

Yes, @sidoh , having the same issue when deploying the lambda within a VPC.