Everyone likes optimization, small file sizes and such.. Won't it be great if you are able to reduce your Docker image sizes by a factor of 2 or more. Say hello to Alpine Linux. It is a minimal Linux distro weighing just 5 MBs. It also has basic linux tools and a nice package manager APK. APK is quite stable and has a considerable amount of packages.
apk add python gcc
In this post, my main motto is how to squeeze the best out of AlpineLinux to create the smallest possible Docker image. So let's start.
Step 1: Use AlpineLinux based images
Ok, I know that's obvious but just for the sake of completeness of this article, I will state that prefer using Alpine based images wherever possible. Python and Redis have their official Alpine based images whereas NodeJS has good unoffical Alpine-based images. Same goes for Postgres, Ruby and other popular environments.
Step 2: Install only needed dependencies
Prefer installing select dependencies over installing a package that contains lots of them. For example, prefer installing
gcc and development libraries over buildpacks.
You can find listing of Alpine packages on their website.
Pro Tip - A great list of Debian v/s Alpine development packages is at alpine-buildpack-deps Docker Hub page (scroll down to Packages). It is a very complete list and you will always find the dependency you are looking for.
Step 3: Delete build dependencies after use
Build dependencies are required by components/libraries to build native extensions for the platform. Once the build is done, they are not needed. So you should delete the build-dependencies after their job is complete. Have a look at the following snippet.
RUN apk add --virtual build-dependencies gcc python-dev linux-headers musl-dev postgresql-dev \ && pip install -r requirements.txt \ && apk del build-dependencies
I am using
--virtual to give a label to the pacakages installed on that instance and then when
pip install is done, I am deleting them.
Step 4: Remove cache
Cache can take up lots of un-needed space. So always run
apk add with
RUN apk add --no-cache package1 package2
If you are using npm for manaing project dependencies and bower for managing frontend dependencies, it is recommended to clear their cache too.
RUN npm cache clean && bower cache clean
Step 5: Learn from the experts
Each and every image on Docker Hub is open source, meaning that it's Dockerfile is freely available. Since the official images are made as efficient as possible, it's easy to find great tricks on how to achieve optimum performance and compact size in them. So when viewing an image on DockerHub, don't forget to peek into its Dockerfile, it helps more than you can imagine.
That's all I have for now. I will keep you updated on new tips if I find any. In my personal experience, I found AlpineLinux to be worth using. I tried deploying Open Event Server on Alpine but faced some issues so ended up creating a Dockerfile using debain:jessie. But for small projects, I would recommend Alpine. On large and complex projects however, you may face issues with Alpine at times. That maybe due to lack of packages, lack of library support or some other thing. But it's not impossible to overcome those issues so if you try hard enough, you can get your app running on Alpine.