Confluence 6. introduces Synchrony (allowing collaborative editing) which cannot accept AJP connections. The preferred configuration is Using Apache with mod_proxy.
Unfortunately, I believe there is a mistake in the Confluence instructions... so after posting my questions here are my notes to figure this all out.
ProxyRequests Off
I believe I've found the error. It probably has to do with the search engine. On the test server's application server - with more memory and updated OS and newer Java - making this batch.js request results in a response. However, on the restricted environment it does not,
wget http://localhost:8090/wiki/s/ca6b4214dc4957e5b90edfd999cd552a-CDN/en_US/8100/e6b42acaec191a9bce4ab234dae0b1b08af15496/e00352cb0013a1867dc5de3984f0fae4/_/download/contextbatch/js/confluence-search-ui-plugin-main,-_super/batch.js?locale=en-US
Let's start with Java,
Not working server = java version "1.8.0_74" 32-bit
Working = java version "1.8.0_221" 64-bit
Now with matching Java version at least, but not 64-bit.
I noticed that "synchrony version" does not show up on startup of the system with the issue,
04-Aug-2019 21:50:06.328 INFO [Catalina-utility-2] org.springframework.web.context.support.AnnotationConfigWebApplicationContext.loadBeanDefinitions Registering annotated classes: [class com.atlassian.synchrony.proxy.websocket.WebSocketConfig,class com.atlassian.synchrony.proxy.web.SynchronyWebMvcConfig] 2019-08-04 21:50:06,648 INFO [Catalina-utility-1] [com.atlassian.confluence.lifecycle] contextInitialized Starting Confluence 6.15.7 [build 8100 based on commit hash e6b42acaec191a9bce4ab234dae0b1b08af15496] - synchrony version 2.1.0-release-confluence_6.15-32f7299a SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder". SLF4J: Defaulting to no-operation (NOP) logger implementation
Now with matching Java version at least, but not 64-bit.
I noticed that "synchrony version" does not show up on startup of the system with the issue,
04-Aug-2019 21:50:06.328 INFO [Catalina-utility-2] org.springframework.web.context.support.AnnotationConfigWebApplicationContext.loadBeanDefinitions Registering annotated classes: [class com.atlassian.synchrony.proxy.websocket.WebSocketConfig,class com.atlassian.synchrony.proxy.web.SynchronyWebMvcConfig] 2019-08-04 21:50:06,648 INFO [Catalina-utility-1] [com.atlassian.confluence.lifecycle] contextInitialized Starting Confluence 6.15.7 [build 8100 based on commit hash e6b42acaec191a9bce4ab234dae0b1b08af15496] - synchrony version 2.1.0-release-confluence_6.15-32f7299a SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder". SLF4J: Defaulting to no-operation (NOP) logger implementation
Ok same Java version including 64-bit...