An example .dockerignore file for Rails

.dockerignore

.git
.gitignore

# Created by https://www.gitignore.io/api/git,ruby,rails,jetbrains+all
# Edit at https://www.gitignore.io/?templates=git,ruby,rails,jetbrains+all

### Git ###
# Created by git for backups. To disable backups in Git:
# $ git config --global mergetool.keepBackup false
*.orig

# Created by git when using merge tools for conflicts
*.BACKUP.*
*.BASE.*
*.LOCAL.*
*.REMOTE.*
*_BACKUP_*.txt
*_BASE_*.txt
*_LOCAL_*.txt
*_REMOTE_*.txt

### JetBrains+all ###
# Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio and WebStorm
# Reference: https://intellij-support.jetbrains.com/hc/en-us/articles/206544839

# User-specific stuff
.idea/**/workspace.xml
.idea/**/tasks.xml
.idea/**/usage.statistics.xml
.idea/**/dictionaries
.idea/**/shelf

# Generated files
.idea/**/contentModel.xml

# Sensitive or high-churn files
.idea/**/dataSources/
.idea/**/dataSources.ids
.idea/**/dataSources.local.xml
.idea/**/sqlDataSources.xml
.idea/**/dynamic.xml
.idea/**/uiDesigner.xml
.idea/**/dbnavigator.xml

# Gradle
.idea/**/gradle.xml
.idea/**/libraries

# Gradle and Maven with auto-import
# When using Gradle or Maven with auto-import, you should exclude module files,
# since they will be recreated, and may cause churn.  Uncomment if using
# auto-import.
# .idea/modules.xml
# .idea/*.iml
# .idea/modules
# *.iml
# *.ipr

# CMake
cmake-build-*/

# Mongo Explorer plugin
.idea/**/mongoSettings.xml

# File-based project format
*.iws

# IntelliJ
out/

# mpeltonen/sbt-idea plugin
.idea_modules/

# JIRA plugin
atlassian-ide-plugin.xml

# Cursive Clojure plugin
.idea/replstate.xml

# Crashlytics plugin (for Android Studio and IntelliJ)
com_crashlytics_export_strings.xml
crashlytics.properties
crashlytics-build.properties
fabric.properties

# Editor-based Rest Client
.idea/httpRequests

# Android studio 3.1+ serialized cache file
.idea/caches/build_file_checksums.ser

### JetBrains+all Patch ###
# Ignores the whole .idea folder and all .iml files
# See https://github.com/joeblau/gitignore.io/issues/186 and https://github.com/joeblau/gitignore.io/issues/360

.idea/

# Reason: https://github.com/joeblau/gitignore.io/issues/186#issuecomment-249601023

*.iml
modules.xml
.idea/misc.xml
*.ipr

# Sonarlint plugin
.idea/sonarlint

### Rails ###
*.rbc
capybara-*.html
.rspec
/db/*.sqlite3
/db/*.sqlite3-journal
/public/system
/coverage/
/spec/tmp
rerun.txt
pickle-email-*.html

# Ignore all logfiles and tempfiles.
/log/*
/tmp/*
!/log/.keep
!/tmp/.keep

# TODO Comment out this rule if you are OK with secrets being uploaded to the repo
config/initializers/secret_token.rb
config/master.key

# Only include if you have production secrets in this file, which is no longer a Rails default
# config/secrets.yml

# dotenv
# TODO Comment out this rule if environment variables can be committed
.env

## Environment normalization:
/.bundle
/vendor/bundle

# these should all be checked in to normalize the environment:
# Gemfile.lock, .ruby-version, .ruby-gemset

# unless supporting rvm < 1.11.0 or doing something fancy, ignore this:
.rvmrc

# if using bower-rails ignore default bower_components path bower.json files
/vendor/assets/bower_components
*.bowerrc
bower.json

# Ignore pow environment settings
.powenv

# Ignore Byebug command history file.
.byebug_history

# Ignore node_modules
node_modules/

# Ignore precompiled javascript packs
/public/packs
/public/packs-test
/public/assets

# Ignore yarn files
/yarn-error.log
yarn-debug.log*
.yarn-integrity

# Ignore uploaded files in development
/storage/*
!/storage/.keep

### Ruby ###
*.gem
/.config
/InstalledFiles
/pkg/
/spec/reports/
/spec/examples.txt
/test/tmp/
/test/version_tmp/
/tmp/

# Used by dotenv library to load environment variables.
# .env

# Ignore Byebug command history file.

## Specific to RubyMotion:
.dat*
.repl_history
build/
*.bridgesupport
build-iPhoneOS/
build-iPhoneSimulator/

## Specific to RubyMotion (use of CocoaPods):
#
# We recommend against adding the Pods directory to your .gitignore. However
# you should judge for yourself, the pros and cons are mentioned at:
# https://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control
# vendor/Pods/

## Documentation cache and generated files:
/.yardoc/
/_yardoc/
/doc/
/rdoc/

/.bundle/
/lib/bundler/man/

# for a library or gem, you might want to ignore these files since the code is
# intended to run in multiple environments; otherwise, check them in:
# Gemfile.lock
# .ruby-version
# .ruby-gemset

# unless supporting rvm < 1.11.0 or doing something fancy, ignore this:

# End of https://www.gitignore.io/api/git,ruby,rails,jetbrains+all

cool