I’m currently working on moving a Tomcat-based application into EC2. The code was written for Java 5.0. While Java 6 would probably work, I’d like to keep everything as “same” as possible, since EC2 presents its own challenges. I spun up a couple of t1.micro instances and copied everything over, including the Java 5 JDK, jdk-1_5_0_22-linux-amd64.rpm. Installing from RPM was easy, but the EC2 instance defaults to using OpenJDK 1.6:

[root@ec2 ~]# java -version
java version "1.6.0_20"
OpenJDK Runtime Environment (IcedTea6 1.9.10) (amazon-52.1.9.10.40.amzn1-x86_64)
OpenJDK 64-Bit Server VM (build 19.0-b09, mixed mode)

There were a couple of things I had to do to get the system to accept the Sun JDK as its “real” java.

Alternatives

Red Hat’s “alternatives” system is designed to allow a system to have multiple versions of a program installed and make it easy to choose which one you want to run. Unfortunately I’ve found the syntax a bit strange and always have to Google it, so I figured I’d document it here for posterity.

So here’s the default:

[root@ec2 ~]# alternatives --config java

There is 1 program that provides 'java'.

  Selection    Command
-----------------------------------------------
*+ 1           /usr/lib/jvm/jre-1.6.0-openjdk.x86_64/bin/java

Enter to keep the current selection[+], or type selection number: 

Here’s how to add Sun java, assuming the java binary is in /usr/java/jdk1.5.0_22/jre/bin/java (where the RPM puts it).

[root@ec2 ~]# alternatives --install /usr/bin/java java /usr/java/jdk1.5.0_22/jre/bin/java 1
[root@ec2 ~]# alternatives --config java
There are 2 programs which provide 'java'.

  Selection    Command
-----------------------------------------------
*+ 1           /usr/lib/jvm/jre-1.6.0-openjdk.x86_64/bin/java
   2           /usr/java/jdk1.5.0_22/jre/bin/java

Enter to keep the current selection[+], or type selection number: 2
[root@ec2 ~]# java -version
java version "1.5.0_22"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_22-b03)
Java HotSpot(TM) 64-Bit Server VM (build 1.5.0_22-b03, mixed mode)

Yay! Unfortunately this doesn’t help with the other problem I had with Tomcat, which was that EC2 instances set the JAVA_HOME var to OpenJDK as well (/usr/lib/jvm/jre). Fortunately this is an easy fix as well.

Setting JAVA_HOME

The JAVA_HOME var is set in /etc/profile.d/aws-apitools-common.sh. Comment out this line:

export JAVA_HOME=/usr/lib/jvm/jre

Create a new file, /etc/profile.d/sun-java.sh, and put this in it:

export JAVA_HOME=/usr/java/jdk1.5.0_22/jre

Also in that file I added the following to instruct the JVM to process all dates in America/New_York, since that’s the timezone all of our other servers use, and it makes reading log files easier when all dates are in the same tz:

export TZ=America/New_York

(I found I had to do this even after pointing /etc/localtime to the correct zoneinfo – Java was stuck on UTC even after the rest of the system was using America/New_York.)