WebSphere Application Server V7.0: Concepts ... - IBM Redbooks

► You can use the WebSphere Application Server rollout update feature, which
requires the application server be stopped. Although it can be used when
there are multiple applications in each application server, all applications are
stopped as the application server is stopped. You need to have all
applications clustered to have other instances always available.
► Each application will receive its own SystemOut and SystemErr log file. If
multiple applications are deployed on the same application server, system log
output from all applications would be interleaved in the SystemOut and
SystemErr logs. Usually, this is not a problem because applications often use,
for example, log4j (which is configurable) to perform logging instead of plain
system out print statements.
► It is simple to diagnose problems as there is only one application in the JVM.
The advantages of deploying multiple applications to the same application server
are as follows:
► By deploying multiple applications to the same application server, you can
reduce the memory used. Each application server instance requires about
130 MB of RAM for it to run. If you have 10 such application server processes
running on your system, you have consumed more than 1 GB worth of RAM
for the WebSphere Application Server runtime alone.
► You can use EJB local interfaces to make local calls from one application to
another, because they are in the same JVM.
► Fewer application servers means fewer ports open in the WebSphere
Application Server tier, which means fewer ports need to be opened in the
firewall between the HTTP tier and the WebSphere Application Server tier.
Sometimes, a mixed approach is the best way to go. By grouping related or
similar applications and deploying them to the same application server, while
deploying other applications that need to run in their own environment, you can
achieve a good compromise.
308 WebSphere Application Server V7.0: Concepts, Planning, and Design