Dockerizing Spring Boot Applications: Makings of a Better Docker Image

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Dockerizing Spring Boot Applications Makings of a Better Docker Image VEDRAN PAVIĆ

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About Me – Vedran Pavić Java Engineer & Team Lead at Infinum Check out what we do at https://infinum.co Spring user for over a decade Contributor to Spring projects since 2015 Collaborator with Spring Security team – Spring Session committer since 2016

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Benefits of Dockerizing More control over runtime - JVM Consistency across different environments Eliminate works on my machine problems Standardized packaging and distribution Use Docker registry for applications as we do Maven repository for libraries Build once, deploy everywhere – separation between build/release and deployment phases

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Demo: four-liner

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Four-liner approach Executable JAR pitfalls Limitations with some APIs (e.g. java.nio.file.Path) Performance implications – check out blog post by Dave Syer: https://spring.io/blog/2018/12/12/how-fast-is-spring Make JAR, not WAR – what actually matters more is how you run it No reuse, no caching – slow pushes and pulls Everything’s in the same layer

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Demo: layered image

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Layered image approach Addresses shortcomings of four-liner approach Requires unpacking of executable JAR Build plugin to handle all of this? Several build plugin available, however unpacking is regularly an extra step

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Enter Google’s Jib Opinionated view on building containers Goals: fast, reproducible, daemonless Plugins for both Gradle & Maven Still relatively new 0.1.0 in Feb 2018, 1.0.0 in Jan 2019

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Demo: Jib plugin

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Reproducible builds matter Read more at https://reproducible-builds.org Jib handles Docker image side of reproducibility But your application needs to play nice too! Remove non-deterministic behavior from your build Enemy of the state: java.util.Properties#store

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Demo: Reproducible image

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Spring 5.2 improvements Support for writing properties in repeatable manner https://github.com/spring-projects/spring-framework/issues/23018 Upcoming Spring Boot 2.2 will leverage those