连接池-实践（待补充）

  • 连接池是什么？它的实现原理？
  • 连接池需要自动处理 Connection Reset 这类错误吗？为什么？不需要，上层做
  • When to use connection pool? typical usage?
  • https 有什么区别吗？

一些基础

TCP keep-alive 和 HTTP keep-alive

  • TCP keep-alive: 每隔一段时间，一端发一个会 keep alive 的包，如果收到回复，则认为连接正常。
  • HTTP keep-alive: 超过多少次或者超时才会关闭连接

HTTPS

HTTPS 看起来是在 TCP 和 HTTP 中间加了一层 TLS/SSL

ConnectionPool Overview

关于连接池的几个结论

  1. 当连接出现问题，连接池会废弃掉这个连接
  2. 当出现 Connection Reset 等错误，连接池没有义务自动重试，一般应用应该允许偶然出现的 Connection
  3. 连接池技术大概有 10 年之久了，非常成熟

Connection Reset Simulation

start a server which supports persistent connections.
from werkzeug.serving import WSGIRequestHandler
from flask import Flask

app = Flask(__name__)


@app.route('/')
def index():
    return 'hello world'


WSGIRequestHandler.protocol_version = "HTTP/1.1"
app.run()
capture packet using tcpdump
# capture packet send to/by port 5000(only fin/syn packet)
sudo tcpdump -i lo port 5000 and "tcp[tcpflags] & (tcp-fin|tcp-syn) != 0"
create a client, send one get request (see tcpdump output)
import requests


s = requests.Session()

url = 'http://127.0.0.1:5000/'
s.get(url)
s.get(url)
intercept packet and kill server
    ```shell
    # add an iptables rule:
    #  intercept all packet sended from port 5000
    sudo iptables -A OUTPUT -p tcp --source-port 5000 -j DROP

    # restart server
    # Ctrl-C and start, or use kill

    # lookup all OUTPUT rules
    sudo iptables -L OUTPUT --line-numbers
    # delete iptables rule
    sudo iptables -D OUTPUT 1
    ```
use http client to send another GET request
s.get(url)
# it will raise:
#  ConnectionError: ('Connection aborted.', error(104, 'Connection reset by peer'))

13:22:43.728133 IP localhost.35126 > localhost.5000: Flags [P.], seq 2568123039:2568123183, ack 2754994964, win 359, options [nop,nop,TS val 3406097304 ecr 3405909308], length 144
13:22:43.728157 IP localhost.5000 > localhost.35126: Flags [R], seq 2754994964, win 0, length 0

Updated:

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