python - aiohttp并发GET请求导致ClientConnectorError(8, 'nodename nor servname provided, or not known')

Question

我被一个看似与 asyncio + aiohttp 相关的问题难住了，当发送大量并发 GET 请求时，超过 85% 的请求会引发 aiohttp.client_exceptions.ClientConnectorError异常最终源于

socket.gaierror(8, 'nodename nor servname provided, or not known')

发送单个 GET 请求或在主机/端口上进行基础 DNS 解析时不会引发此异常。

虽然在我的真实代码中，我正在做大量的自定义，例如使用自定义 TCPConnector例如，我可以仅使用“默认”aiohttp 类实例和参数重现该问题，如下所示。

我跟踪了回溯，异常的根源与 DNS 解析有关。它来自 _create_direct_connection aiohttp.TCPConnector 的方法，调用 ._resolve_host() .

我也试过:

• 使用(和不使用)aiodns
• sudo killall -HUP mDNSResponder
• 使用 family=socket.AF_INET 作为 TCPConnector 的参数(尽管我很确定这被 aiodns 使用)。这使用 2 而不是该参数的默认 int 0
• 使用 ssl=True 和 ssl=False

一切都无济于事。

---

要重现的完整代码如下。输入 URL 位于 https://gist.github.com/bsolomon1124/fc625b624dd26ad9b5c39ccb9e230f5a。 .

import asyncio
import itertools

import aiohttp
import aiohttp.client_exceptions

from yarl import URL

ua = itertools.cycle(
    (
        "Mozilla/5.0 (X11; Linux i686; rv:64.0) Gecko/20100101 Firefox/64.0",
        "Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.10; rv:62.0) Gecko/20100101 Firefox/62.0",
        "Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.13; ko; rv:1.9.1b2) Gecko/20081201 Firefox/60.0",
        "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36"
    )
)

async def get(url, session) -> str:
    async with await session.request(
        "GET",
        url=url,
        raise_for_status=True,
        headers={'User-Agent': next(ua)},
        ssl=False
    ) as resp:
        text = await resp.text(encoding="utf-8", errors="replace")
        print("Got text for URL", url)
        return text

async def bulk_get(urls) -> list:
    async with aiohttp.ClientSession() as session:
        htmls = await asyncio.gather(
            *(
                get(url=url, session=session)
                for url in urls
            ),
            return_exceptions=True
        )
        return htmls


# See https://gist.github.com/bsolomon1124/fc625b624dd26ad9b5c39ccb9e230f5a
with open("/path/to/urls.txt") as f:
    urls = tuple(URL(i.strip()) for i in f)

res = asyncio.run(bulk_get(urls))  # urls: Tuple[yarl.URL]

c = 0
for i in res:
    if isinstance(i, aiohttp.client_exceptions.ClientConnectorError):
        print(i)
        c += 1

print(c)  # 21205 !!!!! (85% failure rate)
print(len(urls))  # 24934

从 res 打印每个异常字符串看起来像:

Cannot connect to host sigmainvestments.com:80 ssl:False [nodename nor servname provided, or not known]
Cannot connect to host giaoducthoidai.vn:443 ssl:False [nodename nor servname provided, or not known]
Cannot connect to host chauxuannguyen.org:80 ssl:False [nodename nor servname provided, or not known]
Cannot connect to host www.baohomnay.com:443 ssl:False [nodename nor servname provided, or not known]
Cannot connect to host www.soundofhope.org:80 ssl:False [nodename nor servname provided, or not known]
# And so on...

---

令人沮丧的是，我可以毫无问题地ping这些主机，甚至可以调用底层的._resolve_host():

重击/外壳:

 [~/] $ ping -c 5 www.hongkongfp.com
PING www.hongkongfp.com (104.20.232.8): 56 data bytes
64 bytes from 104.20.232.8: icmp_seq=0 ttl=56 time=11.667 ms
64 bytes from 104.20.232.8: icmp_seq=1 ttl=56 time=12.169 ms
64 bytes from 104.20.232.8: icmp_seq=2 ttl=56 time=12.135 ms
64 bytes from 104.20.232.8: icmp_seq=3 ttl=56 time=12.235 ms
64 bytes from 104.20.232.8: icmp_seq=4 ttl=56 time=14.252 ms

--- www.hongkongfp.com ping statistics ---
5 packets transmitted, 5 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 11.667/12.492/14.252/0.903 ms

python :

In [1]: import asyncio 
   ...: from aiohttp.connector import TCPConnector 
   ...: from clipslabapp.ratemgr import default_aiohttp_tcpconnector 
   ...:  
   ...:  
   ...: async def main(): 
   ...:     conn = default_aiohttp_tcpconnector() 
   ...:     i = await asyncio.create_task(conn._resolve_host(host='www.hongkongfp.com', port=443)) 
   ...:     return i 
   ...:  
   ...: i = asyncio.run(main())                                                                                                                               

In [2]: i                                                                                                                                                     
Out[2]: 
[{'hostname': 'www.hongkongfp.com',
  'host': '104.20.232.8',
  'port': 443,
  'family': <AddressFamily.AF_INET: 2>,
  'proto': 6,
  'flags': <AddressInfo.AI_NUMERICHOST: 4>},
 {'hostname': 'www.hongkongfp.com',
  'host': '104.20.233.8',
  'port': 443,
  'family': <AddressFamily.AF_INET: 2>,
  'proto': 6,
  'flags': <AddressInfo.AI_NUMERICHOST: 4>}]

---

我的设置:

• python 3.7.1
• aiohttp 3.5.4
• 发生在 Mac OSX High Sierra 和 Ubuntu 18.04 上

---

关于异常本身的信息:

异常是 aiohttp.client_exceptions.ClientConnectorError，它将 socket.gaierror 包装为底层 OSError。

因为我在 asyncio.gather() 中有 return_exceptions=True，所以我可以自己获取异常实例以供检查。这是一个例子:

In [18]: i
Out[18]:
aiohttp.client_exceptions.ClientConnectorError(8,
                                               'nodename nor servname provided, or not known')

In [19]: i.host, i.port
Out[19]: ('www.hongkongfp.com', 443)

In [20]: i._conn_key
Out[20]: ConnectionKey(host='www.hongkongfp.com', port=443, is_ssl=True, ssl=False, proxy=None, proxy_auth=None, proxy_headers_hash=None)

In [21]: i._os_error
Out[21]: socket.gaierror(8, 'nodename nor servname provided, or not known')

In [22]: raise i.with_traceback(i.__traceback__)
---------------------------------------------------------------------------
gaierror                                  Traceback (most recent call last)
~/Scripts/python/projects/clab/lib/python3.7/site-packages/aiohttp/connector.py in _create_direct_connection(self, req, traces, timeout, client_error)
    954                 port,
--> 955                 traces=traces), loop=self._loop)
    956         except OSError as exc:

~/Scripts/python/projects/clab/lib/python3.7/site-packages/aiohttp/connector.py in _resolve_host(self, host, port, traces)
    824                 addrs = await \
--> 825                     self._resolver.resolve(host, port, family=self._family)
    826                 if traces:

~/Scripts/python/projects/clab/lib/python3.7/site-packages/aiohttp/resolver.py in resolve(self, host, port, family)
     29         infos = await self._loop.getaddrinfo(
---> 30             host, port, type=socket.SOCK_STREAM, family=family)
     31

/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/asyncio/base_events.py in getaddrinfo(self, host, port, family, type, proto, flags)
    772         return await self.run_in_executor(
--> 773             None, getaddr_func, host, port, family, type, proto, flags)
    774

/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/concurrent/futures/thread.py in run(self)
     56         try:
---> 57             result = self.fn(*self.args, **self.kwargs)
     58         except BaseException as exc:

/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/socket.py in getaddrinfo(host, port, family, type, proto, flags)
    747     addrlist = []
--> 748     for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
    749         af, socktype, proto, canonname, sa = res

gaierror: [Errno 8] nodename nor servname provided, or not known

The above exception was the direct cause of the following exception:

ClientConnectorError                      Traceback (most recent call last)
<ipython-input-22-72402d8c3b31> in <module>
----> 1 raise i.with_traceback(i.__traceback__)

<ipython-input-1-2bc0f5172de7> in get(url, session)
     19         raise_for_status=True,
     20         headers={'User-Agent': next(ua)},
---> 21         ssl=False
     22     ) as resp:
     23         return await resp.text(encoding="utf-8", errors="replace")

~/Scripts/python/projects/clab/lib/python3.7/site-packages/aiohttp/client.py in _request(self, method, str_or_url, params, data, json, cookies, headers, skip_auto_headers, auth, allow_redirects, max_redirects, compress, chunked, expect100, raise_for_status, read_until_eof, proxy, proxy_auth, timeout, verify_ssl, fingerprint, ssl_context, ssl, proxy_headers, trace_request_ctx)
    474                                 req,
    475                                 traces=traces,
--> 476                                 timeout=real_timeout
    477                             )
    478                     except asyncio.TimeoutError as exc:

~/Scripts/python/projects/clab/lib/python3.7/site-packages/aiohttp/connector.py in connect(self, req, traces, timeout)
    520
    521             try:
--> 522                 proto = await self._create_connection(req, traces, timeout)
    523                 if self._closed:
    524                     proto.close()

~/Scripts/python/projects/clab/lib/python3.7/site-packages/aiohttp/connector.py in _create_connection(self, req, traces, timeout)
    852         else:
    853             _, proto = await self._create_direct_connection(
--> 854                 req, traces, timeout)
    855
    856         return proto

~/Scripts/python/projects/clab/lib/python3.7/site-packages/aiohttp/connector.py in _create_direct_connection(self, req, traces, timeout, client_error)
    957             # in case of proxy it is not ClientProxyConnectionError
    958             # it is problem of resolving proxy ip itself
--> 959             raise ClientConnectorError(req.connection_key, exc) from exc
    960
    961         last_exc = None  # type: Optional[Exception]

ClientConnectorError: Cannot connect to host www.hongkongfp.com:443 ssl:False [nodename nor servname provided, or not known

---

为什么我认为这不是操作系统级别本身的 DNS 解析问题？

我可以成功 ping 我的 ISP 的 DNS 服务器的 IP 地址，该地址在 (Mac OSX) 系统偏好设置 > 网络 > DNS 中给出:

 [~/] $ ping -c 2 75.75.75.75
PING 75.75.75.75 (75.75.75.75): 56 data bytes
64 bytes from 75.75.75.75: icmp_seq=0 ttl=57 time=16.478 ms
64 bytes from 75.75.75.75: icmp_seq=1 ttl=57 time=21.042 ms

--- 75.75.75.75 ping statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 16.478/18.760/21.042/2.282 ms
 [~/] $ ping -c 2 75.75.76.76
PING 75.75.76.76 (75.75.76.76): 56 data bytes
64 bytes from 75.75.76.76: icmp_seq=0 ttl=54 time=33.904 ms
64 bytes from 75.75.76.76: icmp_seq=1 ttl=54 time=32.788 ms

--- 75.75.76.76 ping statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 32.788/33.346/33.904/0.558 ms

 [~/] $ ping6 -c 2 2001:558:feed::1
PING6(56=40+8+8 bytes) 2601:14d:8b00:7d0:6587:7cfc:e2cc:82a0 --> 2001:558:feed::1
16 bytes from 2001:558:feed::1, icmp_seq=0 hlim=57 time=14.927 ms
16 bytes from 2001:558:feed::1, icmp_seq=1 hlim=57 time=14.585 ms

--- 2001:558:feed::1 ping6 statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/std-dev = 14.585/14.756/14.927/0.171 ms
 [~/] $ ping6 -c 2 2001:558:feed::2
PING6(56=40+8+8 bytes) 2601:14d:8b00:7d0:6587:7cfc:e2cc:82a0 --> 2001:558:feed::2
16 bytes from 2001:558:feed::2, icmp_seq=0 hlim=54 time=12.694 ms
16 bytes from 2001:558:feed::2, icmp_seq=1 hlim=54 time=11.555 ms

--- 2001:558:feed::2 ping6 statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/std-dev = 11.555/12.125/12.694/0.569 ms

Answer 1

经过进一步调查，这个问题似乎不是由 aiohttp/asyncio 直接引起的，而是两者的限制/限制:

• 您的 DNS 服务器的容量/速率限制
• 系统级打开文件的最大数量。

首先，对于那些希望获得一些增强型 DNS 服务器的人(我可能不会走那条路)，大牌选项似乎是:

• 1.1.1.1(云 torch )
• 8.8.8.8(谷歌公共(public) DNS)
• 亚马逊 53 号公路

(Good intro to DNS 适合像我这样缺乏网络概念的人。)

我做的第一件事是在增强的 AWS EC2 实例上运行上面的内容 - h1.16xlarge 运行 Ubuntu，它是 IO 优化的。我不能说这本身有帮助，但肯定不会造成伤害。我不太熟悉 EC2 实例使用的默认 DNS 服务器，但是在复制上述脚本时，上面带有 errno == 8 的 OSError 消失了。

但是，它出现了一个新的异常，代码为 24 的 OSError，“打开的文件太多”。我的修补程序解决方案(不是说这是最可持续或最安全的)是增加最大文件限制。我这样做是通过:

sudo vim /etc/security/limits.conf
# Add these lines
root    soft    nofile  100000
root    hard    nofile  100000
ubuntu    soft    nofile  100000
ubuntu    hard    nofile  100000

sudo vim /etc/sysctl.conf
# Add this line
fs.file-max = 2097152

sudo sysctl -p

sudo vim /etc/pam.d/commmon_session
# Add this line
session required pam_limits.so

sudo reboot

诚然，我感觉自己在黑暗中徘徊，但将其与 asyncio.Semaphore(1024)(示例 here)结合使用，导致上述两个异常中的 0 个异常被引发:

# Then call this from bulk_get with asyncio.Sempahore(n)
async def bounded_get(sem, url, session) -> str:
    async with sem:
        return await get(url, session)

在约 25000 个输入 URL 中，只有约 100 个 GET 请求返回异常，主要是因为这些网站被合法破坏，完成的总时间在几分钟内，我认为可以接受。