Running Java applications on Docker: practical tips and valuable insights

Fernando BabadopulosTail

@babadopulos

MEMORY ALLOCATION

Exception inthread...java.lang.OutOfMemoryError:Javaheap space

• By default, container will use as much memory and swap as possible

• Can be restricted using -memory, -memory-reservation, —memory-swap

• Java SE 8u121 and earlier : unaware of container’s limited resources

• From Java SE 8u131 and in JDK 9: there is support for cgroup

CPUs and Threads

Estimating PIusing the MonteCarlomethod

0 1

1

πr2 =π/41x1=1

Ntotal

=

π ≈4 Ntotal

LD_PRELOADHack

RANDOM NUMBERS AND SECURITY

haveged - asimpleentropydaemon

DEBUGGING APPLICATIONS

INTEGRATION TESTS

STRATEGY:

- ONE DOCKER-COMPOSE.YML FOR THEAPPLICATION, ANOTHER ONE FOR TESTING

- START SERVICES- RUN APPLICATION- RUN INTEGRATION TESTS- STOP SERVICES

CODE AT

HTTPS://GITHUB.COM/BABADOPULOS/DOCKER-JAVA-ISSUES-DEMO/TREE/MASTER/INTEGRATION-TESTS-SAMPLE

REFERENCES:

Java inside docker: What you must know to not FAIL, byRafael Benevides

HTTPS://DEVELOPERS.REDHAT.COM/BLOG/2017/03/14/JAVA-INSIDE-DOCKER/

CONVERSATIONS WITH ELIJAH ZUPANCIC (@SHITSUKOISARU)

LD_PRELOAD HACK:HTTPS://STACKOVERFLOW.COM/QUESTIONS/22741859/DECEIVE-THE-

JVM-ABOUT-THE-NUMBER-OF-AVAILABLE-CORES-ON-LINUX/22762558#22762558

HTTPS://GITHUB.COM/BABADOPULOS/DOCKER-JAVA-ISSUES-DEMO

Running Java applications on Docker: practical tips and valuable insights

Fernando BabadopulosTail

@babadopulos