This commit fixes an issue when deleting the plugin directory while
executing the remove plugin command. Namely, we take out a file
descriptor on the plugin directory to traverse its contents to obtain
the list of files to delete. We leaked this file descriptor. On
Unix-based filesystems, this is not a problem, deleting the plugin
directory deletes the plugin directory. On Windows though, a delete is
not executed until the last file descriptor is closed. Since we leaked
this file descriptor, the plugin was not actually deleted. This led to
test failures that tried to cleanup left behind temporary directories
but these test failures were just exposing this bug. This commit fixes
this issue by ensuring that we close the file descriptor to the plugin
directory when we are finished with it.
Relates #24266
Today when removing a plugin, we attempt to move the plugin directory to
a temporary directory and then delete that directory from the
filesystem. We do this to avoid a plugin being in a half-removed
state. We previously tried an atomic move, and fell back to a non-atomic
move if that failed. Atomic moves can fail on union filesystems when the
plugin directory is not in the top layer of the
filesystem. Interestingly, the regular move can fail as well. This is
because when the JDK is executing such a move, it first tries to rename
the source directory to the target directory and if this fails with
EXDEV (as in the case of an atomic move failing), it falls back to
copying the source to the target, and then attempts to rmdir the
source. The bug here is that the JDK never deleted the contents of the
source so the rmdir will always fail (except in the case of an empty
directory).
Given all this silliness, we were inspired to find a different
strategy. The strategy is simple. We will add a marker file to the
plugin directory that indicates the plugin is in a state of
removal. This file will be the last file out the door during removal. If
this file exists during startup, we fail startup.
Relates #24252
The plugin cli currently resides inside the elasticsearch jar. This
commit moves it into a plugin-cli jar. This is change alone is a no-op;
it does not change anything about what is loaded at runtime. But it will
allow easier testing (with fixtures in the future to test ES or maven
installation), as well as eventually not loading these classes when
starting elasticsearch.
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