Caching Strategy Reminder for Maven-Based Docker Builds

Luke Patterson Docker, Java, Tutorial 14 Comments

Attention: The following article was published over 6 years ago, and the information provided may be aged or outdated. Please keep that in mind as you read the post.

My local development feedback loop between code change and runnable container was annoyingly long on a Maven-based project I was recently working on. I wanted to speed things up.

The scenario was something like this:

  1. touch/change some source code
  2. docker build
  3. maven downloads the world
  4. maven compiles my project
  5. docker run
  6. touch/change some source code
  7. docker build
  8. maven downloads the world
  9. maven compiles my project
  10. docker run
  11. touch/change some source code
  12. docker build
  13. maven downloads the world
  14. maven compiles my project
  15. docker run

 

I didn’t really enjoy the “maven downloads the world” steps, and wanted to minimize the number of times it needed to run.

Let’s follow along as I make my situation a little better. For illustration, we’ll start off with this generic archetype-created skeleton project:

https://gist.github.com/f901ceaf75b3458c1cd0

 

Things aren’t that bad when I am building back-to-back, e.g.

$ docker build .
  ...
$ docker build .
  ...

Notice that the second build is fast as everything is cached up.

See Also:  Go "On The Fly"

 

But what about when we do something like this:

$ docker build .
  ...
$ touch src/main/java/com/keyholesoftware/blog/App.java
  ...
$ docker build .
  ...

Notice that the second build is unnecessarily slowed down by the redownload portion.

 

I sat around and despaired for a while until I remembered the tricks I’ve seen with selective caching:

https://gist.github.com/cd7eac7ee43d09ccfe89

Let’s try that sequence again.

$ docker build .
 ...
$ touch src/main/java/com/keyholesoftware/blog/App.java
  ...
$ docker build .
  ...

Getting better, but there were still a few downloads going on during the second build. They are related to the surefire test/plugin. Actually this process will help us iron out downloads which are chosen dynamically, and lock those down. In this case, we lock down our surefire provider.

https://gist.github.com/85d3c479d7b5d6868ed3

 

Let’s try that sequence again.

$ docker build .
  ...
$ touch src/main/java/com/keyholesoftware/blog/App.java
  ...
$ docker build .
  ...

So now, unless we change the POM, we don’t have to redownload anything. Nice.

Now the scenario is something like this:

  1. touch/change some source code
  2. docker build
  3. maven downloads the world
  4. maven compiles my project
  5. docker run
  6. touch/change some source code
  7. docker build
  8. maven compiles my project
  9. docker run
  10. touch/change some source code
  11. docker build
  12. maven compiles my project
  13. docker run
See Also:  Got Formik? Yup!

Notice the “maven downloads the world” step only happens once (unless I actually change the POM, of course).

Final Thoughts

There might be better ways to handle some of this (e.g. dependency:resolve/resolve-plugin but that doesn’t seem to work as thoroughly, and probably something with fig), but I mainly wanted to highlight a possible use of the selective adding/caching.

Other Notes:

Thanks for reading!

— Luke Patterson, [email protected]

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