Update documentation around JVM usage to reflect changes (#13350)

* Update documentation around JVM usage to reflect changes

For Logstash `8.0`, java 8 will no longer be supported, and the documentation should
reflect that.

Update troubleshooting documentation - changes made in #13349 should remove the warnings
at startup for fresh installs of Logstash, but upgrading may still have the same issues.

Co-authored-by: João Duarte <jsvd@users.noreply.github.com>
Co-authored-by: Karen Metts <35154725+karenzone@users.noreply.github.com>

docs/static/jvm.asciidoc

@@ -4,9 +4,8 @@
 
 {ls} requires one of these versions:
 
-* Java 8
 * Java 11
-* Java 15 (see <<jdk15-upgrade>> for settings info)
+* Java 17 (see <<jdk17-upgrade>> for settings info)
 
 Use the
 http://www.oracle.com/technetwork/java/javase/downloads/index.html[official
@@ -19,8 +18,8 @@ for the official word on supported versions across releases.
 [NOTE]
 ===== 
 {ls} offers architecture-specific
-https://staging-website.elastic.co/downloads/logstash[downloads] that include
-AdoptOpenJDK 11, the latest long term support (LTS) release of JDK.
+https://www.elastic.co/downloads/logstash[downloads] that include
+Adoptium Eclipse Temurin 17, the latest long term support (LTS) release of the JDK.
 
 Use the LS_JAVA_HOME environment variable if you want to use a JDK other than the
 version that is bundled. 
@@ -61,25 +60,23 @@ install the correct startup method (SysV init scripts, Upstart, or systemd). If
 installation, you may get an error message, and {ls} will not start properly.
 
 [float]
-[[jdk15-upgrade]]
-==== Using JDK 15
+[[jdk17-upgrade]]
+==== Using JDK 17
 
-{ls} supports JDK 15, but you need to update settings in `jvm.options` and
-`log4j2.properties` if: 
+{ls} supports JDK 17, but you need to update settings in `jvm.options` and
+`log4j2.properties` if you are upgrading from  {ls} 7.11.x (or earlier) to 7.12 or later.
 
-* you are upgrading from  {ls} 7.11.x (or earlier) to 7.12 or later, and
-* you are using JDK 15 or later.
 
 [float]
 ===== Updates to `jvm.options`
-In the `config/jvm.options` file, replace all CMS related flags with:
+In the `config/jvm.options` file, remove all CMS related flags:
 
 [source,shell]
 -----
 ## GC configuration
-8-13:-XX:+UseConcMarkSweepGC
-8-13:-XX:CMSInitiatingOccupancyFraction=75
-8-13:-XX:+UseCMSInitiatingOccupancyOnly
+-XX:+UseConcMarkSweepGC
+-XX:CMSInitiatingOccupancyFraction=75
+-XX:+UseCMSInitiatingOccupancyOnly
 -----
 
 For more information about how to use `jvm.options`, please refer to <<jvm-settings>>.

docs/static/troubleshoot/ts-logstash.asciidoc

@@ -29,17 +29,17 @@ Operation not permitted
 
 * Change setting to mount `/tmp` with `exec`.
 * Specify an alternate directory using the `-Djava.io.tmpdir` setting in the `jvm.options` file.
- 
 
-[[ts-startup]] 
+
+[[ts-startup]]
 ==== {ls} start up
- 
-[[ts-illegal-reflective-error]] 
+
+[[ts-illegal-reflective-error]]
 ===== 'Illegal reflective access' errors
 
 // https://github.com/elastic/logstash/issues/10496 and https://github.com/elastic/logstash/issues/10498
 
-Running Logstash with Java 11 results in warnings similar to these:
+After an upgrade, Logstash may show warnings similar to these:
 
 [source,sh]
 -----
@@ -60,15 +60,14 @@ Try adding these values to the `jvm.options` file.
 -----
 --add-opens=java.base/java.security=ALL-UNNAMED
 --add-opens=java.base/java.io=ALL-UNNAMED
---add-opens=java.base/java.nio.channels=org.jruby.dist
---add-opens=java.base/sun.nio.ch=org.jruby.dist
---add-opens=java.management/sun.management=org.jruby.dist
+--add-opens=java.base/java.nio.channels=ALL-UNNAMED
+--add-opens=java.base/sun.nio.ch=org.ALL-UNNAMED
+--add-opens=java.management/sun.management=ALL-UNNAMED
 -----
 
 *Notes:*
 
-* These settings allow Logstash to start without warnings in Java 11, but they
-prevent Logstash from starting on Java 8.
+* These settings allow Logstash to start without warnings.
 * This workaround has been tested with simple pipelines. If you have experiences
 to share, please comment in the
 https://github.com/elastic/logstash/issues/10496[issue].