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Last active August 23, 2017 02:03
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Java in Docker pitfalls presentation
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presentation.md

Java in Docker pitfalls

Why Java is a special case

  • JVM ergonomics
  • Libraries ergonomics

JVM and libraries decide how much memory and how many threads to use. This decision is based on a host hardware configuration. JVM and some libraries are designed to take a full advantage of all available resources.

Docker is a leaking abstraction

  • Docker uses Linux namespaces and cgroups
  • In a docker instance, an application can access a host hardware configuration
  • Java doesn't know about Docker, cgroups and namespaces (before April 2017)

Memory examples

  • What if memory limit is less than JVM wants to allocate for heap
  • What if memory limit is a little bit more than JVM wants to allocate for heap

JVM allocates memory for

  • Heap
  • Metaspace
  • Code
  • GC
  • Threads
  • Native objects

CPU examples

All dockerised JVMs think they exclusevely have all cores.

Java 9 and Java 8 u131(April 2017)

  • CPU limits work out of the box
  • for a memory, JVM option is still required

Q&A

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