I’m pleased to announce the release of Java Buildpack 4.0. This release
has been a big effort for the team over the last couple of months and is
the culmination of a major focus on improving how the JVM runs in a
containerized environment. These improvements have resulted in an updated
Memory Calculator and a new jvmkill Out of Memory agent. Please take a
moment to read the release announcement[1] for more detail about how and
why we made these changes.

The important thing to note about the Java Buildpack 4.0 release is that
it is not 100% compatible with previous application configurations.
Because the memory calculator now accounts for memory regions that were not
accounted for earlier, applications that used to start (but would likely go
OoM under a high load) will no longer start. It is possible to tune an
application's memory configuration to run in small containers, but using
the JVM defaults means that applications will not start in less than ~700M
of memory. The CF default is 1G per container and applications will start
and run nicely in that configuration.

Because of this incompatibility, we’re releasing Java Buildpack 4.0 in
parallel with Java Buildpack 3.16. Java Buildpack 3.x will continue to
remain the default versions for a short time in order to gather feedback
from users and allow a reasonable migration period. We intend for this
parallel release system to go on for 3-6 months, but if there are
significant difficulties, this can be changed. I highly encourage you to
start trying Java Buildpack 4.0 during this period and giving us feedback
in the GitHub issues[2]. Your feedback, with production applications, can
help influence the ongoing behavior of the memory calculator and jvmkill
agent.

Finally I’d like to recognize Andrew Thorburn and Rafael de Albuquerque
Ribeiro for their input into changes that should be made as well as Glyn
Normington and Chris Frost for their efforts in making these changes a
reality.



-Ben Hale
Cloud Foundry Java Experience



[1]: https://www.cloudfoundry.org/just-released-java-buildpack-4-0/
[2]: https://github.com/cloudfoundry/java-buildpack/issues