Configure Apache load balancer with mod proxy

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Revision as of 10:39, 27 June 2019 by Blucecio (talk | contribs) (Define Apache Load-balancer)
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Server setup

The layout may look something like this (we will refer to these names through the rest of the guide).


Define Apache Load-balancer

This server will handle all HTTP requests from site visitors. As you might see, this means even though you run a load balanced system, using only a single load balancer means you still have a SPOF (single point of failure). It is also possible to configure an environment where yet another server will act as the fail-over load-balancer if the first one fails, but this is outside the scope of this guide.

To set up our load-balancer, we use the Apache web-server and its modules mod_proxy and mod_proxy_balancer. These are part of most of the Apache web-server distributions.

First, create a virtual host handling the requests for your domain: ldproxy.org

<VirtualHost *:80>

  ServerName ldproxy.org

  ServerAdmin webmaster@localhost
  DocumentRoot /var/www/html

  ProxyRequests Off
  ProxyPreserveHost On

  Header add Set-Cookie "ROUTEID=.%{BALANCER_WORKER_ROUTE}e; path=/" env=BALANCER_ROUTE_CHANGED
  <Proxy balancer://mycluster>
        BalancerMember "http://eva00:9080" route=1
        BalancerMember "http://192.168.2.11:8080" route=2

        ProxySet lbmethod=byrequests
        ProxySet stickysession=ROUTEID
    </Proxy>

  ProxyPass / balancer://mycluster/
  ProxyPassReverse / balancer://mycluster/

  ErrorLog ${APACHE_LOG_DIR}/proxy-error.log
  CustomLog ${APACHE_LOG_DIR}/proxy-access.log combined

</VirtualHost>

Configure Tomcat

Let's look at the relevant configuration here to set up the load-balancer. Most likely you will also have an Apache web-server installed on this machines, as for accessing the author instance if located on one of this servers with a nice URL. Here we suggest to use a single Tomcat application server for hosting one public instance. Make sure the AJP Port is set correctly to what you have defined in the virtual host configuration of the load-balancer (8009 as the default value used here).

If you want to change the AJP Port of your application server, this can be done here.

Tomcat config: LOGICALDOC_HOME/tomcat/conf/server.xml

<Connector port="8009" protocol="AJP/1.3" (...)>

Now in the same file as we configure the AJP Port server.xml we need to configure the jvmRoute for sticky sessions working correctly. Use the name defined in the virtual host configuration on load-balancer, the route value here separately for the two servers.

<Engine name="Catalina" defaultHost="localhost" jvmRoute="publicXY">

Note: on the LogicalDOC node Tomcat's config you should change publicXY with public1 or public2 depending on the node