在我們日常運維工作中，經常會碰到負載均衡器后端應用代碼更新、臨時剔除后端服務器、排查一主機應用故障等，往往我們會選擇比較粗魯的做法，直接停止或重啟應用服務，讓負載均衡器探測服務不可用將其剔除。這樣帶來的壞處是用戶與服務器已經建立的連接會被中止，開發人員無法對已經停止服務的主機進行調試。現介紹一種較為溫柔的做法，即通過禁用/啟用成員的方式來達到目的。本文針對目前最為流行的負載均衡器逐一進行介紹。包括LVS、Haproxy、F5在命令行模式下的實現(方便與其它管理平臺對接，實現自動化維護)。當然，Haproxy與F5都提供了人性化管理界面，不過只依賴手工來進行操作。
一、LVS負載均衡器
原理
使用LVS自帶的管理工具來實現。
環境說明
Disable VIP:192.168.100.11:80
Disable REAL SERVER:192.168.100.78
實施步驟
1、初始狀態
[devuser@lvsserver ~]# ipvsadm -Ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
TCP 192.168.100.11:80 rr persistent 60
-> 192.168.100.74:80 Route 3 462 464
-> 192.168.100.75:80 Route 3 420 440
-> 192.168.100.76:80 Route 3 431 400
-> 192.168.100.77:80 Route 3 430 432
-> 192.168.100.78:80 Route 3 435 438
2、禁用成員
[devuser@lvsserver ~]# ipvsadm -d -t 192.168.100.11:80 -r 192.168.100.78
3、當前狀態
[devuser@lvsserver ~]# ipvsadm -Ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
TCP 192.168.100.11:80 rr persistent 60
-> 192.168.100.74:80 Route 3 462 464
-> 192.168.100.75:80 Route 3 420 440
-> 192.168.100.76:80 Route 3 431 400
-> 192.168.100.77:80 Route 3 430 432
4、啟用成員
[devuser@lvsserver ~]#ipvsadm -a -t 192.168.100.11:80 -r 192.168.100.78
5、當前狀態
[devuser@lvsserver ~]# ipvsadm -Ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
TCP 192.168.100.11:80 rr persistent 60
-> 192.168.100.74:80 Route 3 462 464
-> 192.168.100.75:80 Route 3 420 440
-> 192.168.100.76:80 Route 3 431 400
-> 192.168.100.77:80 Route 3 430 432
-> 192.168.100.78:80 Route 3 435 438
二、Haproxy負載均衡器
原理
使用Haproxy的socket admin通道來實現。
環境說明
Disable backend:test.tianya.cn
Disable REAL SERVER:192.168.100.78
實施步驟
1、修改haproxy.cfg配置
#vi /usr/local/haproxy/etc/haproxy.cfg
在global域添加socket admin支持并重啟Haproxy服務
global
... ...
stats socket /usr/local/haproxy/HaproxySocket level admin
... ...
2、安裝socat(在任意的兩個socket管道之間建立一個通道，在該通道中交換兩端的數據。)
wget http://www.dest-unreach.org/socat/download/socat-2.0.0-b3.tar.gz
./configure --disable-fips
make;make install
注：disable OpenSSL FIPS support "--disable-fips"，在沒有安裝fips包的情況下make時會提示：
FIPSLD_CC=gcc fipsld -O -D_GNU_SOURCE -Wall -Wno-parentheses -DHAVE_CONFIG_H -I. -I. -c -o socat.o socat.c
/bin/sh: fipsld: command not found
make: *** [socat.o] Error 127
3、禁用成員
#echo "disable server test.tianya.cn/192.168.100.78" | socat stdio /usr/local/haproxy/HaproxySocket
4、啟用成員
#echo "enable server test.tianya.cn/192.168.100.78" | socat stdio /usr/local/haproxy/HaproxySocket
三、F5-LTM負載均衡器
原理
使用F5-iControl開發包Pycontrol對F5設備進行管理。
環境說明
Disable POOL:test.tianya.cn
Disable SERVER:192.168.100.42:80 192.168.100.43:80 192.168.100.44:80
實施步驟
1、部署運行環境
#mkdir -p /home/install;cd /home/install
安裝python環境(略)，要求py2.5或以上。
1.1、安裝SUDS模塊
#wget https://fedorahosted.org/releases/s/u/suds/python-suds-0.3.8.tar.gz
#tar xvfz python-suds-0.3.8.tar.gz
#cd python-suds-0.3.8
#python setup.py install
1.2、安裝PYCONTROL模塊
#wget http://trungale.net/pycontrol.tar.gz
#tar xvfz pycontrol.tar.gz
#cd trunk
#python setup.py install
1.3、校驗安裝結果
#python
>>> import suds >>> import pycontrol.pycontrol as pc >>> suds.__version__ '0.4' >>> suds.__build__ 'GA R699-20100913' >>> pc.__version__ '2.0.1' >>> pc.__build__ 'r83' >>>
2、編寫LB_member.py代碼
# -*- coding: utf-8 -*- """ ---------------------------------------------------------------------------- Disable/Enable F5-LTM POOL member Name: LB_member.py Author: Liu tian si Email: liutiansi@gamil.com Created: 2011/05/08 Version: 1.0 Blog: http://blog.liuts.com Copyright: (c) 2011 ---------------------------------------------------------------------------- """ import sys import time import string import pycontrol.pycontrol as pc """ ---------------------------------------------------------------------------- F5-LTM Disable/Enable Pool member Class ---------------------------------------------------------------------------- __init__() -Initialization F5-BIG object set_pool_member() -Initialization pool and member object member_factory() -Create a pool member object (Common.IPPortDefinition) session_state_factory() -Create a session state object (LocalLB.PoolMember.MemberSessionState) disable_member() -Disable menber methods enable_member() -Enable menber methods ---------------------------------------------------------------------------- """ class F5_LB_menber(): def __init__(self,_hostname,_username,_password): self.b = pc.BIGIP( hostname = _hostname, username = _username, password = _password, fromurl = True, wsdls = ['LocalLB.PoolMember']) self.sstate_seq = self.b.LocalLB.PoolMember.typefactory.create('LocalLB.PoolMember.MemberSessionStateSequence') def set_pool_member(self,pool,members): self.POOL=pool self.members=members self.sstate_seq.item = self.session_state_factory() def member_factory(self, member): ip,port = member.split(':') pmem = self.b.LocalLB.PoolMember.typefactory.create('Common.IPPortDefinition') pmem.address = ip pmem.port = int(port) return pmem def session_state_factory(self): session_states = [] for x in self.members: sstate = self.b.LocalLB.PoolMember.typefactory.create('LocalLB.PoolMember.MemberSessionState') sstate.member = self.member_factory(x) session_states.append(sstate) return session_states def disable_member(self): for x in self.sstate_seq.item: x.session_state = 'STATE_DISABLED' try: self.b.LocalLB.PoolMember.set_session_enabled_state(pool_names = [self.POOL], session_states = [self.sstate_seq]) except Exception, e: print e def enable_member(self): for x in self.sstate_seq.item: x.session_state = 'STATE_ENABLED' try: self.b.LocalLB.PoolMember.set_session_enabled_state(pool_names = [self.POOL], session_states = [self.sstate_seq]) except Exception, e: print e if __name__ == "__main__": if len(sys.argv) < 4: print "Usage %s POOL MEMBER:port[,member1:80,member2:80,member3:80] enable|disable" % sys.argv[0] print "Examples: python LB_member.py app.domain.com 192.168.0.10:80,192.168.0.11:80,192.168.0.12:80 disable" sys.exit() #F5 administrator info hostname="192.168.100.2" username="adminuser" password="adminpass" App=F5_LB_menber(hostname,username,password) #init F5 pool and member CommandParameters = sys.argv[1:] pool=CommandParameters[0] members=string.split(CommandParameters[1],',') App.set_pool_member(pool,members) if CommandParameters[2]=="enable": App.enable_member() elif CommandParameters[2]=="disable": App.disable_member() else: print "opt parameters error!" sys.exit()
3、源碼分析：
3.1、創建一個池成員對象，將用戶傳入的成員列表轉成規范的pool成員，見member_factory()方法;
3.2、創建一個會話狀態對象，追加成員對象到會話狀態當中，見session_state_factory()方法;
3.3、創建一個隊列，將會話狀態對象添加到隊列子項中，同時修改所處狀態，見__init__()、set_pool_member()、disable_member()/enable_member()方法。
4、禁用成員
#python LB_member.py test.tianya.cn 192.168.100.42:80,192.168.100.43:80,192.168.100.44:80 disable
5、啟用成員
#python LB_member.py test.tianya.cn 192.168.100.42:80,192.168.100.43:80,192.168.100.44:80 enable
參考文章
http://devcentral.f5.com/wiki/default.aspx/iControl.CodeShare