docker中python smtplib發送郵件的延遲問題

最近切換公用的發送郵箱服務到docker中發現了一些超時問題,建聯過程發現容器內比在物理機上時間損耗大約在幾百倍以上;

1. 通過在抓包發現.
   
   通過抓包工具發現實際上整個連接建立過程實際耗時很短，但是等到發送郵件時中間大約間隔了2s左右的時間；server已經響應，問題應該出在client端；
2. 排查smtplib源碼，查找原因。

class SMTP:
    """This class manages a connection to an SMTP or ESMTP server.
    SMTP Objects:
        SMTP objects have the following attributes:
            helo_resp
                This is the message given by the server in response to the
                most recent HELO command.

            ehlo_resp
                This is the message given by the server in response to the
                most recent EHLO command. This is usually multiline.

            does_esmtp
                This is a True value _after you do an EHLO command_, if the
                server supports ESMTP.

            esmtp_features
                This is a dictionary, which, if the server supports ESMTP,
                will _after you do an EHLO command_, contain the names of the
                SMTP service extensions this server supports, and their
                parameters (if any).

                Note, all extension names are mapped to lower case in the
                dictionary.

        See each method's docstrings for details.  In general, there is a
        method of the same name to perform each SMTP command.  There is also a
        method called 'sendmail' that will do an entire mail transaction.
        """
    debuglevel = 0
    file = None
    helo_resp = None
    ehlo_msg = "ehlo"
    ehlo_resp = None
    does_esmtp = 0
    default_port = SMTP_PORT

    def __init__(self, host='', port=0, local_hostname=None,
                 timeout=socket._GLOBAL_DEFAULT_TIMEOUT,
                 source_address=None):
        """Initialize a new instance.

        If specified, `host' is the name of the remote host to which to
        connect.  If specified, `port' specifies the port to which to connect.
        By default, smtplib.SMTP_PORT is used.  If a host is specified the
        connect method is called, and if it returns anything other than a
        success code an SMTPConnectError is raised.  If specified,
        `local_hostname` is used as the FQDN of the local host in the HELO/EHLO
        command.  Otherwise, the local hostname is found using
        socket.getfqdn(). The `source_address` parameter takes a 2-tuple (host,
        port) for the socket to bind to as its source address before
        connecting. If the host is '' and port is 0, the OS default behavior
        will be used.

        """
        self._host = host
        self.timeout = timeout
        self.esmtp_features = {}
        self.command_encoding = 'ascii'
        self.source_address = source_address

        if host:
            (code, msg) = self.connect(host, port)
            if code != 220:
                raise SMTPConnectError(code, msg)
        # 問題出在這
        if local_hostname is not None:
            self.local_hostname = local_hostname
        else:
            # RFC 2821 says we should use the fqdn in the EHLO/HELO verb, and
            # if that can't be calculated, that we should use a domain literal
            # instead (essentially an encoded IP address like [A.B.C.D]).
            fqdn = socket.getfqdn()
            if '.' in fqdn:
                self.local_hostname = fqdn
            else:
                # We can't find an fqdn hostname, so use a domain literal
                addr = '127.0.0.1'
                try:
                    addr = socket.gethostbyname(socket.gethostname())
                except socket.gaierror:
                    pass
                self.local_hostname = '[%s]' % addr

既然連接建立完了,爲什麼還卡在這呢,分析源碼發現,如果不傳local_hostname會嘗試取本機的ip,由於容器採用的網絡模式爲host模式,在這個地方獲取本機花費了很久的時間,因此只要傳入一個本機ip就可以解決.諮詢架構的同學在每個容器的環境變量中有保存本機ip,取出來傳入即可,解決問題,發送郵件又像物理機上一樣快了.