The java version checker requires being written with java 7 APIs.
In order to use java 8 apis in other launcher utilities, this commit
moves the java version checker back to its own jar.
JDK 9 has removed JVM options that were valid in JDK 8 (e.g., GC logging
flags) and replaced them with new flags that are not available in JDK
8. This means that a single JVM options file can no longer apply to JDK
8 and JDK 9, complicating development, complicating our packaging story,
and complicating operations. This commit extends the JVM options syntax
to specify the range of versions the option applies to. If the running
JVM matches the range of versions, the flag will be used to start the
JVM otherwise the flag will be ignored.
We implement this parser in Java for simplicity, and with this we start
our first step towards a Java launcher.
Relates #27675
Today our shell scripts march on if they encounter an error during
execution. One place that this actually causes a problem is with the
Java version checker. What can happen is this: if the user botches their
installation so that the JavaVersionChecker can not be found on the
classpath, when we attempt to run the Java version checker, first an
error message that the class can not be found is displayed, and then we
print a message that their version of Java is not compatible; this
happens even if they are using a Java 8 installation. The problem is
that we should have immediately aborted when the class could not be
loaded. Since we do not exit when the shell script encounters an error,
we end up conflating failue to run the version check with a failed
version check. Instead, we really should abort the moment that one of
our scripts encounters an error. To do this, we make the following
changes:
- enable set -e and set -o pipefail
- make the Java version checker responsible for printing the error
message to the console
- remove the exit status check from the scripts
- actually on Windows, we still have to check the exit status because
there is no equivalent of set -e
- when we check for daemonization, we can no longer check the exit
status from grep because a failed grep will abort the script;
instead, we move the grep execution to be the condition for the if as
this does not trip the set -e failure conditions
- we should source elasticsearch-env before doing anything, so we move
the definition of parse_jvm_options below sourcing elasticsearch-env
- we make consistent all places where we use a subshell to use
backticks
Relates #26057
Today when users start Elasticsearch with their Java configuration
pointing to a pre-Java 8 install, they encounter a cryptic message:
Exception in thread "main" java.lang.UnsupportedClassVersionError:
org/elasticsearch/bootstrap/Elasticsearch : Unsupported major.minor
version 52.0
They often think that they have Java 8 installed but if their JAVA_HOME
or other configuration is causing them to start with a pre-Java 8
install, this error message does not help them.
We introduce a Java version checker that runs on Java 6 as part of the
startup scripts. If the Java version is pre-Java 8, we can display a
helpful error message to the user informing them of the Java version
that the runtime was started with. Otherwise, Elasticsearch starts as it
does today.
Ryan Ernst
Jason Tedor