These fields can be final, since they are set at construction, and
changing them after that could lead to some confusing test cases. This
commit allows the compiler to enforce that we never modify these values
during tests.
This commit more closely aligns the assertion that we are running in a
package distribution with disabling the systemd integration if somehow
we running on not a package distribution. This is, previously we had an
assertion that we are in a package distribution (RPM or Debian package)
but would disable the systemd integration if we are not on
Linux. Instead, we should disable the systemd integration if we are not
running in a package distribution. Because of our assertion, we expect
this to never hold, but we need a fallback for when this assertion is
violated and assertions are not enabled.
Today our systemd service defaults to a service type of simple. This
means that systemd assumes Elasticsearch is ready as soon as the
ExecStart (bin/elasticsearch) process is forked off. This means that the
service appears ready long before it actually is, so before it is ready
to receive requests. It also means that services that want to depend on
Elasticsearch being ready to start can not as there is not a reliable
mechanism to determine this. This commit changes the service type to
notify. This requires that Elasticsearch sends a notification message
via libsystemd sd_notify method. This commit does that by using JNA to
invoke this native method. Additionally, we use this integration to also
notify systemd when we are stopping.
Jason Tedor