Failing to get EC2 instance metadata from the IMDSv2 API when running on EC2 instances

Start in codeguru_profiler_agent/agent_metadata/aws_ec2_instance.py at the token lookup, then inspect codeguru_profiler_agent/agent_metadata/fleet_info.py and the corresponding test mentioned in the issue. Reproduce the IMDSv2 request behavior and update the test mock to match the documented response. Done means EC2 metadata is retrieved through IMDSv2 without the HTTP 405 failure.

The amazon-codeguru-profiler-python-agent fails to get EC2 instance metadata from the IMDSv2 api when running on EC2 instances due to using a GET request to fetch the token when a PUT request is required. I don't really know what the impact is because as the logs note: Unable to get Ec2 instance metadata, this is normal when running in a different environment (e.g. Fargate), profiler will still work. So the profiler seems to still work on EC2 instances but just doesn't have the EC2 instance metadata.

Simplified program to reproduce issue:

import logging
import time

from codeguru_profiler_agent import Profiler

if __name__ == '__main__':
    logging.basicConfig(level=logging.DEBUG)
    Profiler(profiling_group_name='MyProfilingGroup').start()
    time.sleep(30)

Relevant logs from running the program on an EC2 instance with IMDSv2 with python 3.7 and codeguru-profiler-agent 1.2.4:

...
DEBUG:codeguru_profiler_agent.agent_metadata.fleet_info:Making a request to http://169.254.169.254/latest/api/token with headers set for these keys: dict_keys(['X-aws-ec2-metadata-token-ttl-seconds'])
INFO:codeguru_profiler_agent.agent_metadata.aws_ec2_instance:Unable to get Ec2 instance metadata, this is normal when running in a different environment (e.g. Fargate), profiler will still work
DEBUG:codeguru_profiler_agent.agent_metadata.aws_ec2_instance:Caught exception: 
Traceback (most recent call last):
  File "/opt/env/lib/python3.7/site-packages/codeguru_profiler_agent/agent_metadata/aws_ec2_instance.py", line 68, in look_up_metadata
    token = cls.__look_up_ec2_api_token()
  File "/opt/env/lib/python3.7/site-packages/codeguru_profiler_agent/agent_metadata/aws_ec2_instance.py", line 62, in __look_up_ec2_api_token
    headers={EC2_METADATA_TOKEN_TTL_HEADER_KEY: EC2_METADATA_TOKEN_TTL_HEADER_VALUE}) \
  File "/opt/env/lib/python3.7/site-packages/codeguru_profiler_agent/agent_metadata/fleet_info.py", line 26, in http_get
    return request.urlopen(req, timeout=METADATA_URI_TIMEOUT_SECONDS)  # nosec
  File "/usr/local/lib/python3.7/urllib/request.py", line 222, in urlopen
    return opener.open(url, data, timeout)
  File "/usr/local/lib/python3.7/urllib/request.py", line 531, in open
    response = meth(req, response)
  File "/usr/local/lib/python3.7/urllib/request.py", line 641, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/local/lib/python3.7/urllib/request.py", line 569, in error
    return self._call_chain(*args)
  File "/usr/local/lib/python3.7/urllib/request.py", line 503, in _call_chain
    result = func(*args)
  File "/usr/local/lib/python3.7/urllib/request.py", line 649, in http_error_default
    raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 405: Not Allowed
...

Looks like the issue was introduced in this PR here: https://github.com/aws/amazon-codeguru-profiler-python-agent/pull/24 and the test didn't catch it because the mock doesn't doesn't match the IMDSv2 API responses.

For the instance metadata docs see https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/configuring-instance-metadata-service.html#instance-metadata-v2-how-it-works and https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/instancedata-data-retrieval.html where it notes only a PUT request is allowed for fetching the token while the agent uses a GET request: https://github.com/aws/amazon-codeguru-profiler-python-agent/blob/main/codeguru_profiler_agent/agent_metadata/aws_ec2_instance.py#L61 which is why the request fails and returns HTTP Error 405: Not Allowed.

So the fix looks to be change the agent to use a PUT request to get the token and fix the corresponding test.