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聊聊服务端热更新

随着Devops以及微服务的普及,应用上线周期变短,对于以前那种需要停机升级的忍受度也在不断的降低,话不多说,进入主题。

我们需要解决的

tXcilt.png
对于我们来说,我们所需要解决的是:当我们运行着一个服务进程的时候,我们期望这个进程能够突然之间变成新的(新的代码逻辑),并且外部无感知。至少包含几点:

  • 服务状态不丢失:比如监控状态,正在处理的数据状态
  • 服务不中断:用户不能够感知到服务被中断

抱着这样的目的,我们来看看我们是怎么解决的。

方案一:逻辑热更新

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+-------------------------------------------------+
| |
| 动 态 脚 本 运 行 层 |
| |
+-------------------------------------------------+
+-------------------------------------------------+
| |
| C++/Java/Go 数 据 接 收 层 |
| |
+-------------------------------------------------+

这种方案是比较常见的一种解决方案,由于嵌入到进程里面的脚本语言引擎,本质上是将脚本语言代码翻译成内存中的Opcode来执行,因此这类型服务器实现“热更新”方案很简单:将新的脚本同步到服务器上,然后给服务器发出一个信号,重新读取脚本代码到内存中即可。

tXRJ78.png

注意点

  1. 脚本应该是在测试环境验证过的,如果上传了错误的脚本很容易带来灾难性的后果,笔者的公司对此需要走上线审计流程
  2. 对于长时间运行的请求需要保留旧的脚本,直到处理完成。
  3. 对于运行层本身的升级就需要停机或者是自举的方式了。

例子

其实这种热更新方案是有很多的类似或者是说形变的例子,我们就探讨一两个。

Log4j2 日志系统

对于日志系统来说,我们经常需要动态的更新日志系统的 Level,比如将 Info -> Warn 这样的操作,如果大家记得话,我们在服务器上将 Logback.xml 的文件进行修改,大概在一段时间之后,我们的日志级别就会变成我们想要的。这里就是一个标准的动态能力的形变。

org.apache.logging.log4j.core.LoggerContext

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public void updateLoggers() {
updateLoggers(this.configuration);
}

public void updateLoggers(final Configuration config) {
final Configuration old = this.configuration;
for (final Logger logger : loggerRegistry.getLoggers()) {
logger.updateConfiguration(config);
}
}

对于所有的 Logger 对象来说,都有一个相对应的 Configuration 对象,这就是对 Logger 对象的配置,此配置就是我们在 Logback.xml 中的配置,对于 Logback来说,我们需要监听我们的文件是否有所变动即可,代码在 org.apache.logging.log4j.core.util.WatchManager 不做展开了。

Shardingsphere 动态配置

WIP

方案二:来个网关

软件工程中不能解决的问题就加一个中间层来解决(:doge),来吧我们看看一个中间层的解决方案

tXWfIS.png

基于网关控制新的流量,因为我们启动了2个版本的服务实例,此时我们按照时间线切分,在特定时间之后的请求都转发到新的服务器上去。这样对于用户来说是无感知的,不过我们增加一个需要共享内存的操作,对于简单的业务系统来说,我们可以将所有的数据持久化到数据中作为状态的储存,但是还是有一些,比如 prometheus 这一类型的系统,本身就是很多状态数据的,此时我们势必要加入一个共享内容的机制。

例子

这个实现在很多公司来说叫 灰度发布

isito 灰度发布

现在做灰度发布的方案很多种,我们举一个现在流行的 isito 的解决之道。
tXIoDA.png

比如我们有一个 addedvalues 的服务
txmtIJ.png,在线上已经有了 50%/50% 的对于 V1和V2版本来说,这个时候我们需要上线一个新版,将所有的流量转发到新的服务上。
txmHoQ.png

这个时候,我们所需要做的很简单,直接修改CRD即可

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apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
name: addedvalues
spec:
hosts:
- addedvalues
http:
- route:
- destination:
host: addedvalues
Sub set: v2
weight: 50
- destination:
host: addedvalues
subset: v1
weight: 50
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apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
name: addedvalues
spec:
hosts:
- addedvalues
http:
- route:
- destination:
host: addedvalues
subset: v3
weight: 100

一切是如此的简单,CNCF的魅力真是糟糕的藏不住啊。

Spring Cloud 优雅停机

txK3sP.png
对于 Spring Cloud 体系来说,因为我们增加服务发现组件,此时我们并不一定需要网关才能做到这样的事情,我们可以采用一种变形实现方式,其实本质上都是类似的采用所谓的中间层,让外部无感知。如果有兴趣可以参考 Spring的优雅停机

方案三: Socket 所有权转让

我们之前都是通过用户侧的方案来实现,其实还有一种实现方式,笔者也是查阅 Envoy 的实现才发现有这么个机制。

让我们回忆一下远古的 Socket 编程。
txlHoT.png

对于 Socket 编程来说,按照 Linux的 一切皆文件的朴质的哲学思想,对用户体系暴露的是一个 FD,如下图
txlvl9.png

我们在内核用户之间是一个管理关系的,这层就是为了做到我们可以在多个进程之间共享我们打开的FD的句柄,比如我们两个程序同时打开一个文件,其实对于内核来说我们仅仅打开一个文件,只是维护了不同的 sek
tx1iFO.png

因此我们可以发现对于用户态看到的 FD 其实是一个内核 FD 的一个影子代号,那我们是不是可以用一种方式分享我们 ServerSocket 给不同的用户。以达到这样的效果:

tx1a7V.png

例子

转让 ServerSocket: 基于Enovy的简化

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import subprocess
import os
import time

if __name__ == '__main__':
sp = subprocess.Popen(["python3", "children.py"])
time.sleep(3)
sp = subprocess.Popen(["python3", "parent.py"])

time.sleep(99999)
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import socket, select
import array
import sys
import multiprocessing
import os
import time
import pwd
import grp
import logging
import threading

logger = logging.getLogger()
logging.basicConfig(format='%(asctime)-15s pid=%(process)d %(side)s: %(message)s', level=logging.INFO)

EOL1 = b'\n\n'
EOL2 = b'\n\r\n'
response = b'HTTP/1.0 200 OK\r\nDate: Mon, 1 Jan 1996 01:01:01 GMT\r\n'
response += b'Content-Type: text/plain\r\nContent-Length: 13\r\n\r\n'
response += b'Hello, world!'

running = True
shutdonwing = False


# Function from https://docs.python.org/3/library/socket.html#socket.socket.sendmsg
def send_fds(sock, msg, fds):
return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))])


def new_send_fd(socket_filename, send_sock):
sock = socket.socket(family=socket.AF_UNIX)

logger.info("Connecting to socket file '%s'" % socket_filename, extra={"side": "SEND ==>"})
e = None
for _ in range(10):
try:
sock.connect(socket_filename)
break
except OSError as e:
logger.error("Socket file '%s' not available yet, try %d/10 (%s)" % (socket_filename, _, e),
extra={"side": "SEND ==>"})
time.sleep(0.5)
pass
else: # nobreak
raise e

logger.info("Connected", extra={"side": "SEND ==>"})

logger.info("Sender delaying 10s to demonstrate a blocking receiver...", extra={"side": "SEND ==>"})
time.sleep(10)
file_descriptor_int = send_sock.fileno()
logger.info("Sending file descriptors %d" % file_descriptor_int, extra={"side": "SEND ==>"})
send_fds(sock, b"some payload", [file_descriptor_int])

global running
running = False
global shutdonwing
shutdonwing = True

def shutdonw():
time.sleep(5)
global shutdonwing
shutdonwing = False

if __name__ == '__main__':
try:
serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serversocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
serversocket.bind(('0.0.0.0', 8080))
serversocket.listen(1)
serversocket.setblocking(True)

threading.Thread(target=new_send_fd, args=("/tmp/uds_socket", serversocket)).start()

epoll = select.epoll()
epoll.register(serversocket.fileno(), select.EPOLLIN)
connections = {}
requests = {}
responses = {}
while running:
events = epoll.poll(1)
for fileno, event in events:
if fileno == serversocket.fileno():
connection, address = serversocket.accept()
connection.setblocking(0)
epoll.register(connection.fileno(), select.EPOLLIN)
connections[connection.fileno()] = connection
requests[connection.fileno()] = b''
responses[connection.fileno()] = response
elif event & select.EPOLLIN:
requests[fileno] += connections[fileno].recv(1024)
if EOL1 in requests[fileno] or EOL2 in requests[fileno]:
epoll.modify(fileno, select.EPOLLOUT)
#print('-' * 40 + '\n' + requests[fileno].decode()[:-2])
elif event & select.EPOLLOUT:
byteswritten = connections[fileno].send(responses[fileno])
responses[fileno] = responses[fileno][byteswritten:]
if len(responses[fileno]) == 0:
epoll.modify(fileno, 0)
connections[fileno].shutdown(socket.SHUT_RDWR)
elif event & select.EPOLLHUP:
epoll.unregister(fileno)
connections[fileno].close()
del connections[fileno]
threading.Thread(target=shutdonw).start()
while shutdonwing:
events = epoll.poll(1)
for fileno, event in events:
if fileno == serversocket.fileno():
pass
elif event & select.EPOLLIN:
requests[fileno] += connections[fileno].recv(1024)
if EOL1 in requests[fileno] or EOL2 in requests[fileno]:
epoll.modify(fileno, select.EPOLLOUT)
# print('-' * 40 + '\n' + requests[fileno].decode()[:-2])
elif event & select.EPOLLOUT:
byteswritten = connections[fileno].send(responses[fileno])
responses[fileno] = responses[fileno][byteswritten:]
if len(responses[fileno]) == 0:
epoll.modify(fileno, 0)
connections[fileno].shutdown(socket.SHUT_RDWR)
elif event & select.EPOLLHUP:
epoll.unregister(fileno)
connections[fileno].close()
del connections[fileno]
finally:
epoll.unregister(serversocket.fileno())
epoll.close()
# serversocket.close()
print("parent will stopping........")
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import socket, select
import array
import sys
import multiprocessing
import os
import time
import pwd
import grp

import logging

logger = logging.getLogger()
logging.basicConfig(format='%(asctime)-15s pid=%(process)d %(side)s: %(message)s', level=logging.INFO)

EOL1 = b'\n\n'
EOL2 = b'\n\r\n'
response = b'HTTP/1.0 200 OK\r\nDate: Mon, 1 Jan 1996 01:01:01 GMT\r\n'
response += b'Content-Type: text/plain\r\nContent-Length: 13\r\n\r\n'
response += b'Hello, world!'


# Function from https://docs.python.org/3/library/socket.html#socket.socket.recvmsg
def recv_fds(sock, msglen, maxfds):
fds = array.array("i") # Array of ints
msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize))
for cmsg_level, cmsg_type, cmsg_data in ancdata:
if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS):
# Append data, ignoring any truncated integers at the end.
fds.fromstring(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)])
return msg, list(fds)


def new_recv_fd(socket_filename):
try:
os.remove("/tmp/uds_socket")
except OSError:
pass

logger.info('Starting privledges: %d/%d = %s/%s' % \
(os.getuid(),
os.getgid(),
pwd.getpwuid(os.getuid())[0],
grp.getgrgid(os.getgid())[0]), extra={"side": "<== RECV"})

if os.getuid() == 0:
running_uid = pwd.getpwnam("nobody")[2]
running_gid = grp.getgrnam("nogroup")[2]
os.setgid(running_gid)
os.setuid(running_uid)

logger.info('Dropped privledges: currently %d/%d = %s/%s' % \
(os.getuid(),
os.getgid(),
pwd.getpwuid(os.getuid())[0],
grp.getgrgid(os.getgid())[0]), extra={"side": "<== RECV"})

logger.info("Receiver delaying creation of socket to demonstrate sender retries...", extra={"side": "<== RECV"})
logger.info("Binding to (and creating) AF_UNIX socket socket file '%s'" % socket_filename,
extra={"side": "<== RECV"})
sock = socket.socket(family=socket.AF_UNIX)
sock.bind(socket_filename)
sock.listen()
logger.info("Socket listening %s" % sock, extra={"side": "<== RECV"})

# Waste a file descriptor, so the fd numbers on source and receive sides don't match (they'll be both 6 by default)
leak_a_file_descriptor = open("/etc/hosts")

if not hasattr(sock, "recvmsg"):
raise RuntimeError(
"We don't have a `Socket.recvmsg` in this implementation of python (eg, system python 2.7 on OSX")

# Accept exactly 1 connection
client, info = sock.accept()
logger.info("Connected, client=%s" % client, extra={"side": "<== RECV"})

logger.info("Blocking until message is received", extra={"side": "<== RECV"})
msg, fds = recv_fds(client, 100, 4)
logger.info("Received message msg=%s fds=%s" % (msg, fds), extra={"side": "<== RECV"})
return fds[0]


if __name__ == '__main__':

fdno = new_recv_fd("/tmp/uds_socket")
logger.info("got from parent fd %d" % (fdno), extra={"side": "<== RECV"})
serversocket = socket.socket(fileno=fdno)
# serversocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
# serversocket.bind(('0.0.0.0', 8080))
# serversocket.listen(1)
# serversocket.setblocking(True)

epoll = select.epoll()
epoll.register(serversocket.fileno(), select.EPOLLIN)
try:
connections = {}
requests = {}
responses = {}
while True:
events = epoll.poll(1)
for fileno, event in events:
if fileno == serversocket.fileno():
connection, address = serversocket.accept()
connection.setblocking(0)
epoll.register(connection.fileno(), select.EPOLLIN)
connections[connection.fileno()] = connection
requests[connection.fileno()] = b''
responses[connection.fileno()] = response
elif event & select.EPOLLIN:
requests[fileno] += connections[fileno].recv(1024)
if EOL1 in requests[fileno] or EOL2 in requests[fileno]:
epoll.modify(fileno, select.EPOLLOUT)
#print('-' * 40 + '\n' + requests[fileno].decode()[:-2])
elif event & select.EPOLLOUT:
byteswritten = connections[fileno].send(responses[fileno])
responses[fileno] = responses[fileno][byteswritten:]
if len(responses[fileno]) == 0:
epoll.modify(fileno, 0)
connections[fileno].shutdown(socket.SHUT_RDWR)
elif event & select.EPOLLHUP:
epoll.unregister(fileno)
connections[fileno].close()
del connections[fileno]
finally:
epoll.unregister(serversocket.fileno())
epoll.close()
serversocket.close()

运行结果如下:

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✗ python3 main.py
2020-06-13 23:54:28,647 pid=114797 <== RECV: Starting privledges: 1000/1000 = yanick/yanick
2020-06-13 23:54:28,647 pid=114797 <== RECV: Receiver delaying creation of socket to demonstrate sender retries...
2020-06-13 23:54:28,647 pid=114797 <== RECV: Binding to (and creating) AF_UNIX socket socket file '/tmp/uds_socket'
2020-06-13 23:54:28,647 pid=114797 <== RECV: Socket listening <socket.socket fd=3, family=AddressFamily.AF_UNIX, type=SocketKind.SOCK_STREAM, proto=0, laddr=/tmp/uds_socket>
2020-06-13 23:54:31,657 pid=114804 SEND ==>: Connecting to socket file '/tmp/uds_socket'
2020-06-13 23:54:31,657 pid=114804 SEND ==>: Connected
2020-06-13 23:54:31,657 pid=114804 SEND ==>: Sender delaying 10s to demonstrate a blocking receiver...
2020-06-13 23:54:31,657 pid=114797 <== RECV: Connected, client=<socket.socket fd=5, family=AddressFamily.AF_UNIX, type=SocketKind.SOCK_STREAM, proto=0, laddr=/tmp/uds_socket>
2020-06-13 23:54:31,657 pid=114797 <== RECV: Blocking until message is received
2020-06-13 23:54:41,667 pid=114804 SEND ==>: Sending file descriptors 3
children.py:77: DeprecationWarning: fromstring() is deprecated. Use frombytes() instead.
msg, fds = recv_fds(client, 100, 4)
2020-06-13 23:54:41,668 pid=114797 <== RECV: Received message msg=b'some payload' fds=[6]
2020-06-13 23:54:41,669 pid=114797 <== RECV: got from parent fd 6
parent will stopping........

我们查看两次监听的状态也可以发现Socket本身变化了

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netstat -tunlp
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:8080 0.0.0.0:* LISTEN 114804/python3

netstat -tunlp
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:8080 0.0.0.0:* LISTEN 114797/python3

源码地址: 需要Python3+

注意点

  • 我们并没没有完整的处理好长连接的 Socket,具体可以参考 [方案四](#方案三的升级: 方案四: 方案三的升级)
  • 值得注意的我们需要打开 EpollLT 模式,因为对于父亲节点有一些是不处理的,因为涉及到进程抢占,需要再次通知。
  • 另外 Linux 转让 FD 的方式据笔者查阅也仅有 Unix Socket 模式,这一部分功能是平台绑定的。

转让 ClientSocket

因为在方案三中我们良好的处理长连接的 Socket,因为我们只是简单的处理了 ServerSocket,但是由此可得:如果可以把正在处理的 ClienSocket 和 它所在的状态一同转换到新的进程上,我们也可以完成这样的事情不是么?

这一次我们简化下网络请求,使用简单的传统 Blocking IO, 当我们第 N 次访问的时候返回 N 的结果。

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telnet 127.0.0.1 8080
1
0 got message: b'1\r\n'
2
1 got message: b'2\r\n'

同上略

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import socket
import array
import os
import time
import logging
import threading

logger = logging.getLogger()
logging.basicConfig(format='%(asctime)-15s pid=%(process)d %(side)s: %(message)s', level=logging.INFO)

running = True


# Function from https://docs.python.org/3/library/socket.html#socket.socket.sendmsg
def send_fds(sock, msg, fds):
return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))])


def new_send_fd(socket_filename, send_sock, i):
sock = socket.socket(family=socket.AF_UNIX)
global running
running = False
logger.info("Connecting to socket file '%s'" % socket_filename, extra={"side": "SEND ==>"})
e = None
for _ in range(10):
try:
sock.connect(socket_filename)
break
except OSError as e:
logger.error("Socket file '%s' not available yet, try %d/10 (%s)" % (socket_filename, _, e),
extra={"side": "SEND ==>"})
time.sleep(0.5)
pass
else: # nobreak
raise e

logger.info("Connected", extra={"side": "SEND ==>"})
logger.info("Sender delaying 10s to demonstrate a blocking receiver...", extra={"side": "SEND ==>"})
time.sleep(10)
file_descriptor_int = send_sock.fileno()
logger.info("Sending file descriptors %d, state: %d" % (file_descriptor_int, i), extra={"side": "SEND ==>"})
send_fds(sock, b"some payload", [file_descriptor_int, i])


def new_connection(conn, status):
i = status
threading.Thread(target=new_send_fd, args=("/tmp/uds_socket", conn, i)).start()
while running:
data = conn.recv(1024)
logger.info("Got Message At %d" % os.getpid(), extra={"side": "SEND ==>"})
if not data:
break
conn.sendall(bytes(("%d got message: %s\n" % (i, data)), 'utf-8'))
i += 1


if __name__ == '__main__':
try:
serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serversocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) # 设置了 reusea 简化配置
serversocket.bind(('0.0.0.0', 8080))
serversocket.listen()
logger.info("server listening at 8080", extra={"side": "SEND ==>"})
while True:
conn, addr = serversocket.accept()
threading.Thread(target=new_connection, args=(conn, 0)).start()
finally:
serversocket.close()

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import socket
import array
import threading
import os
import pwd
import grp, time

import logging

logger = logging.getLogger()
logging.basicConfig(format='%(asctime)-15s pid=%(process)d %(side)s: %(message)s', level=logging.INFO)


# Function from https://docs.python.org/3/library/socket.html#socket.socket.recvmsg
def recv_fds(sock, msglen, maxfds):
fds = array.array("i") # Array of ints
msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize))
for cmsg_level, cmsg_type, cmsg_data in ancdata:
if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS):
# Append data, ignoring any truncated integers at the end.
fds.fromstring(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)])
return msg, list(fds)


def new_recv_fd(socket_filename):
try:
os.remove("/tmp/uds_socket")
except OSError:
pass

logger.info('Starting privledges: %d/%d = %s/%s' % \
(os.getuid(),
os.getgid(),
pwd.getpwuid(os.getuid())[0],
grp.getgrgid(os.getgid())[0]), extra={"side": "<== RECV"})

if os.getuid() == 0:
running_uid = pwd.getpwnam("nobody")[2]
running_gid = grp.getgrnam("nogroup")[2]
os.setgid(running_gid)
os.setuid(running_uid)

logger.info('Dropped privledges: currently %d/%d = %s/%s' % \
(os.getuid(),
os.getgid(),
pwd.getpwuid(os.getuid())[0],
grp.getgrgid(os.getgid())[0]), extra={"side": "<== RECV"})

logger.info("Receiver delaying creation of socket to demonstrate sender retries...", extra={"side": "<== RECV"})
logger.info("Binding to (and creating) AF_UNIX socket socket file '%s'" % socket_filename,
extra={"side": "<== RECV"})
sock = socket.socket(family=socket.AF_UNIX)
sock.bind(socket_filename)
sock.listen()
logger.info("Socket listening %s" % sock, extra={"side": "<== RECV"})

# Waste a file descriptor, so the fd numbers on source and receive sides don't match (they'll be both 6 by default)
leak_a_file_descriptor = open("/etc/hosts")

if not hasattr(sock, "recvmsg"):
raise RuntimeError(
"We don't have a `Socket.recvmsg` in this implementation of python (eg, system python 2.7 on OSX")

# Accept exactly 1 connection
client, info = sock.accept()
logger.info("Connected, client=%s" % client, extra={"side": "<== RECV"})

logger.info("Blocking until message is received", extra={"side": "<== RECV"})
msg, fds = recv_fds(client, 100, 4)
logger.info("Received message msg=%s fds=%s" % (msg, fds), extra={"side": "<== RECV"})
return fds[0], fds[1]


def new_connection(conn, status):
i = status
is_running = True
with conn:
while is_running:
data = conn.recv(1024)
logger.info("Got Message At %d" % os.getpid(), extra={"side": "SEND ==>"})
if not data:
break
conn.sendall(bytes(("%d got message: %s\n" % (i, data)), 'utf-8'))
i += 1


if __name__ == '__main__':
fdno = new_recv_fd("/tmp/uds_socket")
logger.info("got from parent fd: %d status: %d" % (fdno[0], fdno[1]), extra={"side": "<== RECV"})
threading.Thread(target=new_connection, args=(socket.socket(fileno=fdno[0]), fdno[1])).start()
logger.info("startup server..", extra={"side": "<== RECV"})
time.sleep(100)

访问可得如下的结果:

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$ telnet 127.0.0.1 8080
0 got message: b'\r\n'
1 got message: b'\r\n'
2 got message: b'\r\n'
3 got message: b'\r\n'
4 got message: b'\r\n'

注意点

  • 这里值得注意的是需要处理 clientsocket 的状态:当我们转让 socket 的时候也需要处理好,此时的socket处于的状态。

总结

对于我们来说热升级的集中方案对比

特性 脚本运行层 基于网关 基于Socket
开发效率
性能
架构难度
备注 常见在多变的逻辑层 微服务系统常见 使用的比较少,容易出错

参考

来杯奶茶, 嗝~~~