Making a GET request with urllib3 in python 3.5 is failing with the error CERTIFICATE_VERIFY_FAILED on some sites where the certificate is valid.

import certifi
import urllib3
manager = urllib3.PoolManager(cert_reqs='CERT_REQUIRED', ca_certs=certifi.where())
http.request('GET', 'https://google.com')

Gives this error:

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/site-packages/urllib3/connectionpool.py", line 601, in urlopen
    chunked=chunked)
  File "/usr/local/lib/python3.5/site-packages/urllib3/connectionpool.py", line 346, in _make_request
    self._validate_conn(conn)
  File "/usr/local/lib/python3.5/site-packages/urllib3/connectionpool.py", line 850, in _validate_conn
    conn.connect()
  File "/usr/local/lib/python3.5/site-packages/urllib3/connection.py", line 326, in connect
    ssl_context=context)
  File "/usr/local/lib/python3.5/site-packages/urllib3/util/ssl_.py", line 329, in ssl_wrap_socket
    return context.wrap_socket(sock, server_hostname=server_hostname)
  File "/usr/local/lib/python3.5/ssl.py", line 376, in wrap_socket
    _context=self)
  File "/usr/local/lib/python3.5/ssl.py", line 747, in __init__
    self.do_handshake()
  File "/usr/local/lib/python3.5/ssl.py", line 983, in do_handshake
    self._sslobj.do_handshake()
  File "/usr/local/lib/python3.5/ssl.py", line 628, in do_handshake
    self._sslobj.do_handshake()
ssl.SSLError: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:646)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/site-packages/requests/adapters.py", line 440, in send
    timeout=timeout
  File "/usr/local/lib/python3.5/site-packages/urllib3/connectionpool.py", line 639, in urlopen
    _stacktrace=sys.exc_info()[2])
  File "/usr/local/lib/python3.5/site-packages/urllib3/util/retry.py", line 388, in increment
    raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='google.com', port=443): Max retries exceeded with url: / (Caused by SSLError(SSLError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:646)'),))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.5/site-packages/requests/api.py", line 72, in get
    return request('get', url, params=params, **kwargs)
  File "/usr/local/lib/python3.5/site-packages/requests/api.py", line 58, in request
    return session.request(method=method, url=url, **kwargs)
  File "/usr/local/lib/python3.5/site-packages/requests/sessions.py", line 508, in request
    resp = self.send(prep, **send_kwargs)
  File "/usr/local/lib/python3.5/site-packages/requests/sessions.py", line 618, in send
    r = adapter.send(request, **kwargs)
  File "/usr/local/lib/python3.5/site-packages/requests/adapters.py", line 506, in send
    raise SSLError(e, request=request)
requests.exceptions.SSLError: HTTPSConnectionPool(host='google.com', port=443): Max retries exceeded with url: / (Caused by SSLError(SSLError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:646)'),))

Yet the same request made with the openssl command line succeeds.

openssl s_client -showcerts -connect google.com:443 -CAfile /usr/local/lib/python3.5/site-packages/certifi/cacert.pem

Urllib3 fails for some but not all domains. For example the following succeeds.

http.request('GET', 'https://bbc.com')

This is happening on a kubernetes pod running Debian GNU/Linux 8. Using the python3.5 docker image.