Docker and jvm. A good idea?

Docker and the JVM, a good idea?

Christopher Batey@chbatey

@chbatey

Overview

● Motivation● How they work● What you need to know

○ Tools○ Problems by example

■ Thread per request (Dropwizard/Jetty)■ Thread per core (Ratpack/Netty)

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rat-pack

dropwizard

wiremock

● 12 cores w/ hyper-threading● 64GB RAM

Apache Benchmark

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Motivation

5

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Deployment models

Host

App

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So why?

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Multiple JVMs on the same machine?

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JVM ergonomics

https://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/ergonomics.html

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What

9

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Docker

● Namespaces○ Process○ Mounts○ Networking

● CGroups○ CPU○ Memory

Tools & Examples

12.5

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Tools

● Ps, Htop and Top● Systemd-cg{ls, top}● Dstat● Cadvisor● Heapster● Jcmd● dmesg

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Images

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PID namespace

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Tool: Htop

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Tool: Top

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Tool: systemd-cgls

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Wtf?

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Control Groups (cgroups)

● CPU - shares● Memory - limit

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Resource_Management_Guide/sec-cpu.html

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Resource_Management_Guide/sec-memory.html





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Memory

20

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Limiting memory

Free inside a container

/proc/* is not control group aware

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Limiting memory

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Tool: Dmesg

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More memory

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Survives \o/

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Survives \o/ but is slow :(

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Tool: systemd-cgtop

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Tool: DStat

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Tool: systemd-cgtop

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Tool: Htop

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Disabling swap

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Sizing the memory for a JVM

● Heap● Threads ● Metaspace● Code● GC● Native (direct ByteBuffers and sun.misc.Unsafe)

30

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Native Memory Tracking

-XX:NativeMemoryTracking=summary

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Tool: jcmd

● JCmd allows us to see a JVMs memory usage

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Tool: jcmd

● Jcmd VM.native_memory● 100+ Threads?

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Tool: Jcmd

Jcmd Thread.print

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Wtf?

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Overriding

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Solution?

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Ratpack threads

jcmd 26 Thread.print | grep "ratpack-compute" | wc -l

24

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It isn’t just your web framework

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CPU

40

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Limiting CPU - shares

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Tool: systemd-cgtop

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Understanding CPU shares

1024 512 512

CPU 0 CPU 1

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Understanding CPU shares

1024 512 512

CPU quota

Cpu_period = 100000

One cores = 100000

Two cores = 200000

etc

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That is more like it! Or is it?

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JVM inside containers

● Get an appropriate number of threads● Size memory and test

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Thanks for listening

Github: https://github.com/chbatey/docker-jvm-talk

Twitter: @chbatey

Want to work (in London) with Docker, Rkt, Kubernetes, Go, Java, Python, Cassandra, MySQL? [email protected]

@chbatey

Why I care

● Accidently become a Platform Engineer / Site Reliability Engineer○ Team of three that builds an internal PaaS for 100s of applications

● Tech:○ AWS○ Docker○ Kubernetes (custom build)○ Cassandra○ MySQL○ Prometheus

Docker and jvm. A good idea?

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