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下文給大家?guī)?lái)應(yīng)該如何搭建Apache+tomcat+負(fù)載均衡的環(huán)境，希望能夠給大家在實(shí)際運(yùn)用中帶來(lái)一定的幫助，負(fù)載均衡涉及的東西比較多，理論也不多，網(wǎng)上有很多書(shū)籍，今天我們就用創(chuàng)新互聯(lián)在行業(yè)內(nèi)累計(jì)的經(jīng)驗(yàn)來(lái)做一個(gè)解答。

Apache2.0是一個(gè)標(biāo)準(zhǔn)兼容、快速、成熟的web云服務(wù)器,擅長(zhǎng)提供靜態(tài)內(nèi)容，比如靜態(tài)HTML頁(yè)面和圖片。Tomcat web服務(wù)器處理Java server Pages和Java servlet是很有用的、但在提供靜態(tài)內(nèi)容上沒(méi)有Apache快。因此，如果要要構(gòu)建一個(gè)快速、可伸縮的web應(yīng)用程序，就需要一個(gè)Apache服務(wù)，它提供JSP和servlet請(qǐng)求服務(wù)給多個(gè)tomcat處理，通過(guò)使用一個(gè)Apache模塊、mod_jk（通過(guò)會(huì)話關(guān)聯(lián)的方式執(zhí)行負(fù)載均衡，即“sticky” session）。會(huì)話關(guān)聯(lián)解釋道，當(dāng)客戶端瀏覽器第一次請(qǐng)求一個(gè)JSP頁(yè)面,請(qǐng)求被Apache接收后，負(fù)載平衡器將請(qǐng)求重定向到兩個(gè)tomcat服務(wù)器中的一個(gè);來(lái)自相同規(guī)則的客戶端的進(jìn)一步請(qǐng)求將被自動(dòng)轉(zhuǎn)發(fā)到相同的tomcat服務(wù)器,以便檢索用戶的會(huì)話數(shù)據(jù)。

本文檔描述如何配置Apache 2.x通過(guò)端口偵聽(tīng)的方式，分派JSP和servlet請(qǐng)求到兩個(gè)Tomcat 4.x。這個(gè)設(shè)置是Linux系統(tǒng)上完成的，你的情況可能不同。

1. Download the required software

• Apache 2.x Binaries (If you plan to use ssl, get the source)

• Tomcat 4.x Binaries

• The JK module

2. Compile, Install and Configure Apache

2.1 Install Apache.

Linux: gunzip the *.gz you downloaded, untar and run install-bindist.sh

For *nux, to install Apache 2.0.42 with mod_sll installed, you will need to compile from source:

I used http://httpd.apache.org/docs-2.0/install.html as a reference.

$ lynx http://www.apache.org/dist/httpd/httpd-2.0.42.tar.gz
$ gzip -d httpd-2.0.42.tar.gz
$ tar xvf httpd-2.0.42.tar
$ ./configure --enable-mods-shared=most --enable-ssl=shared
$ make
$ make install

Then download mod_jk-2.0.42.so and put it into your modules directory and rename it mod_jk.so.

Windows: Execute the downloaded executable and install.

2.2 Configure the JK Module in httpd.conf

Edit the Apache server's configuration file httpd.conf which is located in the /usr/local/apache2/conf directory.

2.2.1 Below "# LoadModule foo_module modules/mod_foo.so", insert the following lines:

#
# Load mod_jk
#
LoadModule jk_module modules/mod_jk.so

#
# Configure mod_jk
#
JkWorkersFile conf/workers.properties
JkLogFile logs/mod_jk.log
JkLogLevel info

NOTE: You will need to change mod_jk.so to mod_jk.dll for Windows.

2.2.2 Below the "DocumentRoot" line, insert the following two lines:

JkMount /*.jsp loadbalancer
JkMount /servlet/* loadbalancer

2.3 Create the workers.properties file

Now we will create a file called worker.properties, and we will place it under /usr/local/apache2/conf. The worker.properties file tells Apache about the various Tomcat servers that are running, and on which port they are listening.

In my setup, I installed the two Tomcat servers in different directories, on the same machine as Apache. Feel free to put your Tomcat servers on different machines.

I made the first Tomcat server's AJP13 connector listen on port 11009 instead of the default port which is 8009, and the second one listens on port 12009.

I have decided to name my tomcat servers tomcat1 and tomcat2. This is purely my choice.

Create the file exactly like this:

#
# workers.properties 
#

# In Unix, we use forward slashes:
ps=/

# list the workers by name

worker.list=tomcat1, tomcat2, loadbalancer

# ------------------------
# First tomcat server
# ------------------------
worker.tomcat1.port=11009
worker.tomcat1.host=localhost
worker.tomcat1.type=ajp13

# Specify the size of the open connection cache.
#worker.tomcat1.cachesize

#
# Specifies the load balance factor when used with
# a load balancing worker.
# Note:
#  ----> lbfactor must be > 0
#  ----> Low lbfactor means less work done by the worker.
worker.tomcat1.lbfactor=100


# ------------------------
# Second tomcat server
# ------------------------
worker.tomcat2.port=12009
worker.tomcat2.host=localhost
worker.tomcat2.type=ajp13

# Specify the size of the open connection cache.
#worker.tomcat2.cachesize

#
# Specifies the load balance factor when used with
# a load balancing worker.
# Note:
#  ----> lbfactor must be > 0
#  ----> Low lbfactor means less work done by the worker.
worker.tomcat2.lbfactor=100


# ------------------------
# Load Balancer worker
# ------------------------

#
# The loadbalancer (type lb) worker performs weighted round-robin
# load balancing with sticky sessions.
# Note:
#  ----> If a worker dies, the load balancer will check its state
#        once in a while. Until then all work is redirected to peer
#        worker.
worker.loadbalancer.type=lb
worker.loadbalancer.balanced_workers=tomcat1, tomcat2

#
# END workers.properties
#

That's it, we're done with Apache.

3. Install and Configure the Tomcat Servers

Now let's suppose that Java 1.4.x is installed under /usr/local/jdk1.4.x/. Create two Tomcat 4.x servers and install them under /usr/local/:

   tar fvxz jakarta-tomcat-4.x.tar.gz
   mv jakarta-tomcat-4.x /usr/local/tomcat1 
   cp -R /usr/local/tomcat1 /usr/local/tomcat2

In both /usr/local/tomcat1 and /usr/local/tomcat2, the same files will be modified. I here by present the modifications made to the files contained in the /usr/local/tomcat1 directory tree structure. You should also apply the same changes to the corresponding files located under the /usr/local/tomcat2 directory tree structure.

3.1 Modify catalina.sh

In my many years of consulting, I have learned not to rely on environment variables which can be unset by ignorant or malicious people. This is why I explicitely set the JAVA_HOME and CATALINA_HOME variables directly in the catalina.sh file.

At line 32, before the "# ----- Verify and Set Required Environment Variables " line, insert the following two lines:

    JAVA_HOME=/usr/local/jdk1.4 ; export JAVA_HOME
    CATALINA_HOME=/usr/local/tomcat1 ; export CATALINA_HOME

(Set CATALINA_HOME to /usr/local/tomcat2 in /usr/local/tomcat2/conf/catalina.sh)

3.2 Modify conf/server.xml

3.2.1 Add a unique jvmRoute to the Catalina engine

Near line 100, replace:

with:

For tomcat2, put jvmRoute="tomcat2".

3.2.2 Change the control port

At line 13, replace:

    
with:
    
For the tomcat2 server, replace port 8005 with 12005. This will prevent the two servers from conflicting.
3.2.3 Change the AJP13 port
At line 75, in the AJP 13 connector definition, replace:
    port="8009"
with:
    port="11009"
For the tomcat2 server, replace port 8009 with 12009.
3.2.4 Disable the standalone HTTP port
We don't want or need our tomcat servers to directly respond to HTTP requests. So we comment out the HttpConnector section between lines and 58 in the server.xml file.
Example:

NOTE: If you don't comment this out, you will need to change the port numbers so they don't conflict between tomcat instances.
3.2.5 Disable the WARP connector
At line 314, comment out the  tag.
Example:

Do not forget to do the same thing to tomcat2's server.xml file.
NOTE: You might want to comment out the entire  element. If so, make sure and remove the comments within it - XML doesn't like comments within comments.
3.3 Create test JSP pages (index.jsp)
3.3.1 Create a file named index.jsp and put it in the /usr/local/tomcat1/webapps/ROOT directory:



<%= request.getSession().getId() %>
Tomcat 1

3.3.2 Create a file named index.jsp and put it in the /usr/local/tomcat2/webapps/ROOT directory:



<%= request.getSession().getId() %>
Tomcat 2

4. Start Tomcat1, Tomcat2 and Apache
    /usr/local/tomcat1/bin/startup.sh
    /usr/local/tomcat2/bin/startup.sh
    /usr/local/apache2/bin/apachectl start
5. Test your Installation
Now is the time to test your setup. First, verify that Apache serves static content.
Click on: http://localhost/. You should see the default Apache index.html page.
Now test that tomcat (either Tomcat 1 or Tomcat 2) is serving Java Server Pages.
Click on: http://localhost/index.jsp
If you get a red page, the page was served by the tomcat1 server, and if you get a blue page, it was served by the tomcat2 server.
Now test that session affinity - also known as sticky sessions - works within the load balancer. Hit the reload button of your web browser several times and verify that the index.jsp page you get is always received from the same tomcat server.
6. Configuring Private JVMs
If you don't need load-balancing, but you are interested in configuring Apache/Tomcat for private Tomcat instances, you can add one of the following near the end of httpd.conf:
6.1 Name-based (1 IP address or NIC).
NameVirtualHost *


ServerName localhost1
JkMount /*.jsp tomcat1
JkMount /servlet/* tomcat1



ServerName localhost2
JkMount /*.jsp tomcat2
JkMount /servlet/* tomcat2
6.2 IP-based (different IP for each site).
# First Virtual Host.
#

ServerName localhost
JkMount /*.jsp tomcat1
JkMount /servlet/* tomcat1


# Second Virtual Host.
#

ServerName localhost2
JkMount /*.jsp tomcat2
JkMount /servlet/* tomcat2
Where the serverNames are fully-qualified host names in a DNS Server. More information can be found at http://httpd.apache.org/docs-2.0/vhosts/.
NOTE: When using SSL with multiple Virtual Hosts, you must use an ip-based configuration. This is because SSL requires you to configure a specific port (443), whereas name-based specifies all ports (*). You might the following error if you try to mix name-based virtual hosts with SSL.
[error] VirtualHost _default_:443 -- mixing * ports and non-* ports with a NameVirtualHost address is not supported, proceeding with undefined results
Starting Apache and Tomcat on Startup
To start Apache and Tomcat on startup in a *nix environment, see http://www.raibledesigns.com/tomcat/boot-howto.html.
On Windows, you can install Tomcat as a service.
Supplemental Information
Question 1: 
Why did you choose to use the AJP13 connector rather than the WARP connector that is recommended?
Answer: 
The warp connector is used in conjunction with mod_webapp, and mod_webapp does not currently support load balancing.
Also, I found the documentation for the warp connector on the Jakarta web site to be quite lacking. See: http://jakarta.apache.org/tomcat/tomcat-4.0-doc/config/warp.html
I know that the future lies in the warp connector, but in the meantime, I needed something. The documentation did not explain to me exactly what benefits I would get from using the Warp connector as opposed to AJP13.
Question 2: 
You might specify that creating two instances of the tomcat installation is not needed as you can share the main binaries and libs by specifying 2 distinct CATALINA_BASE variables.
True, but in real life the two tomcat servers are usually located on two different machines. My setup might be overkill for a single machine setup, but it's easy to tar up the "tomcat2" server and put it on a second machine; you just have to change "localhost" to the appropriate machine name in /usr/local/apache2/conf/workers.properties and you're done.
Question 3: 
What does not work and what does work in load balancing?
Answer: 
Load balancing works great.
1. Session affinity works 
Which means that when a client browser is directed to a Tomcat server by the load balancer, then future queries from that same browser session will always be directed to the same tomcat server. This is important because sessions that are created in a specific tomcat server, say "tomcat1", do not exist in the other server "tomcat2", and thus if the client was directed to another tomcat server than the one where his session is stored, then all his session data would be lost.
Some people are working on sessions that will be replicated across all tomcat servers in the cluster, so I'll just wait for it to become available rather than make a homebrewed distributed session mechanism.
The downside of not having sessions replicated across all the tomcat servers in the cluster is that if one tomcat server dies, all the sessions that it contained are lost, which usually makes a lot of unhappy users.
2. Failover works 
If one tomcat server dies, the load balancer then "rebalances" the queries to the remaining tomcat servers.
3. Failback works 
When a tomcat server comes back from the dead, the load balancer automatically starts to send queries to it. So you can actually add capacity to your cluster on the fly.
4. Weighted load balancing works 
In /usr/local/apache2/conf/workers.properties, I assigned a load balancing factor of 100 to both "tomcat1" and "tomcat2" servers. Then I changed the lbfactor of "tomcat1" to 101, and I saw that effectively the "tomcat1" server received more load than the "tomcat2" server, which is something you want when for example your "tomcat1" server is a faster/newer machine while your "tomcat2" server is a slower machine which cannnot take as much load as the other one.
References
For more information, you should read An Apache Load Balancing Cluster. It talks about mod_jserv, which is now mod_jk, and it uses JServ instead of Tomcat, but the concepts are still valid.
Conclusion
The list of steps that are required to obtain a scalable web application solution based on Apache 2.x and a group of distibuted Tomcat servers are well-defined and if you follow the receipe exactly, you should be able to achieve success.
I hope that this article will be helpful to you. Good Luck.
其它環(huán)境搭建：
Monitoring and Managing Tomcat Clusters Using JMX
Clustering and Load Balancing in Tomcat 5, Part 1
Clustering and Load Balancing in Tomcat 5, Part 2
 看了以上關(guān)于應(yīng)該如何搭建Apache+tomcat+負(fù)載均衡的環(huán)境，如果大家還有什么地方需要了解的可以在創(chuàng)新互聯(lián)行業(yè)資訊里查找自己感興趣的或者找我們的專(zhuān)業(yè)技術(shù)工程師解答的，創(chuàng)新互聯(lián)技術(shù)工程師在行業(yè)內(nèi)擁有十幾年的經(jīng)驗(yàn)了。
 
 

            
            
                        

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