[examples/dockerdev] Add .dockerignore

[FunkyloverOne]

Guys, I'm loving your post, but it could be even better for newbies (like me) if it also included .dockerignore file, which is important to make an image-building much faster for bigger projects.

[Envek]

You don't need .dockerignore for dockerized development because you don't add whole directories into development docker image: it contains only Ruby, dependencies to build your gems, and Nodejs for frontend.

[Envek]

But you do need .dockerignore for production build. It will vary a lot between projects, but there is more or less generic example:

# for all code you usually don't want .git history in image, just the current commit you have checked out
.git

# you usually don't want dockerfile and compose files in the image either (to not lost caches on not significant changes)
*Dockerfile*
*docker-compose*
.dockerignore

# Local gems (there should be separate `bundle install` step in Dockerfile)
vendor/bundle/

# Specs or tests (may contain large fixtures)
spec/

# Keys for Rails credentials (they should be mounted into container from outside)
config/master.key
config/credentials/*.key

# CI configuration
.circleci/
.github/

# Backend dev tools
.rspec_status
.rubocop*
.bundle/

# running application artifacts
log/
tmp/
public/system/
public/storage/
public/uploads/

# Frontend
public/packs*
node_modules/

# Developer-specific things. So bad that there is no global .dockerignore. See https://github.com/moby/moby/issues/12843
/.idea/

# What else to exclude?
# - Helm chart or Ansible playbooks or anything deployment-specific, not used in production

[FunkyloverOne]

@Envek I disagree.

I know it sounds weird, but since all those folders are inside of build context - all of them are being sent to the docker engine, and it might take a long time.

Note that I do not copy or add anything, my Dockerfile for development is equal to yours - it only sets up the environment.

I thought that I had some issues with docker and it just stuck. But no, I just had to wait like 3 minutes for all the context files, before the build even started. Then I've added a .dockerignore file, similar to yours here, and it started flying!
It gets straight to the building immediately now.

This is because on my project there's a large node_modules tree, also the project is old, so the .git folder is huge too.

(I found that solution here: docker/compose#4396 (comment))

[Envek]

Ah, yes, you're right! Build context!

Another solution is to limit build context at docker-compose level (see Compose file v2 build section):

--- a/examples/dockerdev/docker-compose.yml
+++ b/examples/dockerdev/docker-compose.yml
@@ -2,8 +2,8 @@ version: '2.4'
 
 x-app: &app
   build:
-    context: .
-    dockerfile: ./.dockerdev/Dockerfile
+    context: .dockerdev
+    dockerfile: Dockerfile
     args:
       RUBY_VERSION: '2.6.3'
       PG_MAJOR: '11'

But that also requires changing .dockerdev/Dockerfile to remove .dockerdev references to current directory:

--- a/examples/dockerdev/.dockerdev/Dockerfile
+++ b/examples/dockerdev/.dockerdev/Dockerfile
@@ -31,7 +31,7 @@ RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - \
   && echo 'deb http://dl.yarnpkg.com/debian/ stable main' > /etc/apt/sources.list.d/yarn.list
 
 # Install dependencies
-COPY .dockerdev/Aptfile /tmp/Aptfile
+COPY Aptfile /tmp/Aptfile
 RUN apt-get update -qq && DEBIAN_FRONTEND=noninteractive apt-get -yq dist-upgrade && \
   DEBIAN_FRONTEND=noninteractive apt-get install -yq --no-install-recommends \
     libpq-dev \

[Envek]

This is because on my project there's a large node_modules tree, also the project is old, so the .git folder is huge too.

(I found that solution here: docker/compose#4396 (comment))

As usually there is .dockerignore for production Dockerfile, .git and node_modules are also being stripped from .dockerdev/Dockerfile build also. That's probably why people doesn't usually notice it 😃

[FunkyloverOne]

Yup, so I believe one of those solutions is worth to be added to your awesome post! 😄
However, at least a reference to .dockerignore and why it is important would be very helpful for those who are getting started.

[Envek]

Also changed the “Ruby on Whales” post accordingly.

[oliverklee]

The changes to the Dockerfile (as mentioned in #26 (comment)) still need to make it into the article.