/docker-build-optimizations

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Docker build optimizations

The aim of this micro project is to show how to optimize your build process with Docker. Btw it's not perfect and will have to be worked on.

Dockerfile example

Here is the content of Dockerfile:

FROM mhart/alpine-node:4.6

# 1. build stuff
RUN npm install lodash
# some 'useful' steps
RUN echo "var _ = require('lodash'); console.log(_.toUpper('hi there!'));" > ./build.js
RUN node build.js > build-artifact

# 2. clean stuff for building environment
RUN rm -rf node_modules && rm -rf ./build.js

We can divide the building process into two parts. The first involves building the artifact and the second, removing useless libraries and tools. The build-artifact is the only thing that we need in the final image.

The problem

The problem is in the intermediate layers:

➜  docker-build-optimizations git:(master) ✗ docker history my-image
IMAGE               CREATED             CREATED BY                                      SIZE                COMMENT
5af424c456c9        16 hours ago        /bin/sh -c rm -rf node_modules && rm -rf ./bu   0 B
8914c03d630a        16 hours ago        /bin/sh -c node build.js > build-artifact       9 B
f7ecf6c407d7        16 hours ago        /bin/sh -c echo "var _ = require('lodash'); c   63 B
d3237dc0b157        16 hours ago        /bin/sh -c npm install lodash                   2.162 MB
dfcbae5ded73        10 days ago         /bin/sh -c apk add --no-cache curl make gcc g   31.34 MB
<missing>           10 days ago         /bin/sh -c #(nop)  ENV VERSION=v4.6.1 NPM_VER   0 B
<missing>           5 weeks ago         /bin/sh -c #(nop) ADD file:d6ee3ba7a4d59b1619   4.803 MB

We don't need d3237dc0b157, f7ecf6c407d7 and 8914c03d630a.

The solution

The one way to solve this issue is to remove these intermediate layers by using docker export/import commands. For more details see docker-build.sh script.

➜  docker-build-optimizations git:(master) ✗ ./docker-build.sh my-image
➜  docker-build-optimizations git:(master) ✗ docker history my-image
IMAGE               CREATED             CREATED BY          SIZE                COMMENT
166d57395cd8        16 hours ago                            36.9 MB             Imported from -

The downsides and the really good solution

So now there is one very small layer and everything in it. Is it perfect? - No. Because in this case Docker cannot cache pulled layers and has to download almost the same stuff every time.

The one solution that seems nice is Rocker's from overloading. Of course you can achieve the same effect with a simple bash-script but it won't be so obvious.