Smallest docker container with elixir app

@gmile You don’t need the -dev libs on the release image.

This should suffice:

 add --no-cache \
      ncurses-libs \
      zlib \
      openssl \
      ca-certificates

@wmnnd this dropped the size to 56 MB, thanks!

How big is the actual release tar file you copy onto the image? The
reason I am asking is that I built alpine from scratch with our erlang
release and it was 18MB where 2/3 (if I remember correctly) was our release.

You should be able to shrink this significantly.

How do you suggest shrinking the release size?

Normally you don’t. You can exclude debug information which will make it
much smaller (half the size?). Without debug information you cannot
do things like tracing and other useful introspection in production. But
if you need the smallest available this is an option.

Generally the release size is the size your image will be + 5MB or so
for alpine.

If you depend on additional system libs that can add quite a bit of weight, depending on what they are. You can also double check to see which Erlang applications are being included, it should only be the subset your application depends on, not all of them.

A medium-sized application would probably depend on enough Erlang libs to hit that limit before any code from their own application was counted. A simple test project of mine hits 23mb with just libs, and here are the ones included in the release:

asn1-5.0/
certifi-1.1.0/
combine-0.9.6/
compiler-7.1/
crypto-4.0/
elixir-1.4.5/
gettext-0.13.1/
hackney-1.8.0/
idna-4.0.0/
iex-1.4.5/
kernel-5.3/
logger-1.4.5/
metrics-1.0.1/
mimerl-1.0.2/
poison-3.1.0/
public_key-1.4.1/
sasl-3.0.4/
ssl-8.2/
ssl_verify_fun-1.1.1/
stdlib-3.4/
test-0.1.0/
timex-3.1.13/
tzdata-0.5.12/

So either your app was extremely small or didn’t depend on much - in any case, I suspect most real-world applications will be much larger than 18mb. ERTS itself is only like 6mb, and anything in priv of your application or your dependencies will also be included.

I strongly recommend not stripping debug info - those cases you mentioned are some of the most powerful capabilities of the runtime, and are one of the reasons why OTP is such a powerful tool operationally. You are trading a small amount of space for a significant amount of functionality, to me it’s not even close to worth it to sacrifice that.

So either your app was extremely small or didn’t depend on much - in any case,
I suspect most real-world applications will be much larger than 18mb. ERTS
itself is only like 6mb, and anything in priv of your application or your
dependencies will also be included.

Yes, it didn’t have many dependencies. My point was that the
release is what should take up the most space. You cannot get the docker image
smaller than the release and that the alpine linux image should have
very little overhead in terms of space.

I strongly recommend not stripping debug info - those cases you mentioned are
some of the most powerful capabilities of the runtime, and are one of the
reasons why OTP is such a powerful tool operationally. You are trading a small
amount of space for a significant amount of functionality, to me it’s not even
close to worth it to sacrifice that.

Agreed. I don’t think the trade-off is worth it either but if you want
the smallest image possible you should know about the option.

We generally encrypt the debug info (we ship our software to clients).
In this case you need the key to be able to do any debugging but it
makes it a little bit harder to reconstruct the source code.

I’ve measured the space taken inside the container, and here’s what I’ve got.

• here’s the root:

  docker run -it gmile/ritm:0.0.9 du / -h -d 1
  0       /dev
  4.0K    /home
  0       /proc
  4.0K    /root
  8.9M    /usr
  4.0K    /tmp
  812.0K  /bin
  80.0K   /var
  0       /sys
  1.3M    /etc
  4.0K    /run
  4.0K    /srv
  4.0K    /mnt
  220.0K  /sbin
  5.3M    /lib
  16.0K   /media
  55.7M   /app
  72.3M   /
  

• here’s the /app folder, containing unpacked tar release:

  docker run -it gmile/ritm:0.0.9 du /app -h -d 1
  52.0K   /app/bin
  380.0K  /app/releases
  33.7M   /app/erts-8.3
  21.6M   /app/lib
  55.7M   /app
  

ERTS itself is only like 6mb

@bitwalker from what I am seeing, erts is 33.7 Mb way bigger than 6 Mb. Any ideas why so?

Upgrading the base image to bitwalker/alpine-elixir:1.4.5 (with erlang 20.0.1 underneath) shaved off another 12 Mb down to 48 Mb. After looking at the size stats, the shrink is due to erts loosing some weight:

docker run -it gmile/ritm:0.0.10 du /app -h -d 1
21.1M   /app/erts-9.0.1
52.0K   /app/bin
380.0K  /app/releases
22.2M   /app/lib
43.7M   /app

The size of erts is still way more than 6 Mb.

You’d have to show what is taking up that space in the ERTS folder - on my laptop, a release packed with ERTS included only shows 5.4mb in the erts-9.0 folder via du -hs <path>. Either there is more in the ERTS folder on Alpine which can be stripped (and I can tweak that in the Alpine images I produce if so) or it’s just bigger on Linux for some reason, but I can’t imagine why that would be.