Well, I broke it 
I’ve installed jdk8, restart tomcat in stage, the initial page loaded, did some database migrations.
I thought it was good and fine, but I had the following problem in demo:
2016-11-17 03:46:42,980 [pool-3-thread-1] INFO conf.BootStrap - Generated new download URL for Release id=1512
2016-11-17 03:46:42,984 [pool-3-thread-1] INFO conf.BootStrap - Generated new download URL for Release id=1513
2016-11-17 03:46:42,989 [pool-3-thread-1] INFO conf.BootStrap - Generated new download URL for Release id=1514
2016-11-17 03:46:42,993 [pool-3-thread-1] INFO conf.BootStrap - Generated new download URL for Release id=1517
2016-11-17 03:46:42,997 [pool-3-thread-1] INFO conf.BootStrap - Generated new download URL for Release id=1518
2016-11-17 03:46:43,001 [pool-3-thread-1] INFO conf.BootStrap - Generated new download URL for Release id=1519
2016-11-17 03:46:43,005 [pool-3-thread-1] INFO conf.BootStrap - Generated new download URL for Release id=1520
2016-11-17 03:46:43,009 [pool-3-thread-1] INFO conf.BootStrap - Generated new download URL for Release id=1521
2016-11-17 03:46:43,013 [pool-3-thread-1] INFO conf.BootStrap - Generated new download URL for Release id=1522
2016-11-17 03:46:43,017 [pool-3-thread-1] INFO conf.BootStrap - Generated new download URL for Release id=1523
2016-11-17 03:46:43,022 [pool-3-thread-1] INFO conf.BootStrap - Generated new download URL for Release id=1524
2016-11-17 03:46:46,831 [pool-3-thread-1] INFO conf.BootStrap - Performing bulk index
2016-11-17 03:47:29,562 [pool-3-thread-1] INFO conf.BootStrap - Starting mirror service
Nov 17, 2016 3:47:30 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory /var/lib/tomcat7/webapps/ROOT
Nov 17, 2016 3:47:30 AM org.apache.catalina.core.ContainerBase addChildInternal
SEVERE: ContainerBase.addChild: start:
org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:154)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:895)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:871)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:615)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1095)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1617)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.tomcat.util.bcel.classfile.ClassFormatException: Invalid byte tag in constant pool: 15
at org.apache.tomcat.util.bcel.classfile.Constant.readConstant(Constant.java:131)
at org.apache.tomcat.util.bcel.classfile.ConstantPool.(ConstantPool.java:60)
at org.apache.tomcat.util.bcel.classfile.ClassParser.readConstantPool(ClassParser.java:209)
at org.apache.tomcat.util.bcel.classfile.ClassParser.parse(ClassParser.java:119)
at org.apache.catalina.startup.ContextConfig.processAnnotationsStream(ContextConfig.java:2032)
at org.apache.catalina.startup.ContextConfig.processAnnotationsJar(ContextConfig.java:1923)
at org.apache.catalina.startup.ContextConfig.processAnnotationsUrl(ContextConfig.java:1891)
at org.apache.catalina.startup.ContextConfig.processAnnotations(ContextConfig.java:1877)
at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1270)
at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:855)
at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:345)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5161)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
… 10 more
Nov 17, 2016 3:47:30 AM org.apache.catalina.startup.HostConfig deployDirectory
SEVERE: Error deploying web application directory /var/lib/tomcat7/webapps/ROOT
java.lang.IllegalStateException: ContainerBase.addChild: start: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[]]
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:898)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:871)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:615)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1095)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1617)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Nov 17, 2016 3:47:30 AM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler [“http-bio-8080”]
Nov 17, 2016 3:47:30 AM org.apache.catalina.startup.Catalina start
INFO: Server startup in 265877 ms
Googling it, it appeared to be the version of tomcat we are using (http://stackoverflow.com/questions/6751920/tomcat-7-servlet-3-0-invalid-byte-tag-in-constant-pool/12730059#12730059 and https://bz.apache.org/bugzilla/show_bug.cgi?id=53735), but it wasn’t not trivial to upgrade. Also, several other test servers have the same version of tomcat!
So, I changed tomcat back to JAVA 7, and rollback 2.4 again. Of course it didn’t come alive

Well, I just decided to roll forward to 2.5 again, but the application is down now 
Can someone please help? @darius @raff @pascal @maany @burke