まずは通常のRuby on Railsアプリと同じくbundle installしてRailsサーバーを立てましょう。

$ bundle install
$ rails server

これでlocalhost:3000でデプロイされるHello World Appが見れました。

gcloud セットアップ

gcloud を使って行きますがいくつか事前の設定が必要あります。

# 初期化
$ gcloud init

# Googleログインする
$ gcloud auth login

# 今回作成したプロジェクトIDをセット
$ gcloud config set project {your-project-id}

$ gcloud preview app deploy

デプロイされたあとは AppEngine Console のバージョンの一覧に出てきます。

デプロイ時のログ

Beginning deployment...
If this is your first deployment, this may take a while...done.

Using Ruby 2.2.4 as requested in the .ruby-version file
Verifying that Managed VMs are enabled and ready.
Building and pushing image for module [default]
Started cloud build [789f0d61-dc0a-4994-8292-02a5ff9f65de].
To see logs in the Cloud Console: https://console.developers.google.com/logs?project=your-project-id&service=cloudbuild.googleapis.com&key1=789f0d61-dc0a-4994-8292-02a5ff9f65de&logName=projects/your-project-id/logs/cloudbuild
--------------------------------- REMOTE BUILD OUTPUT ----------------------------------
starting build "789f0d61-dc0a-4994-8292-02a5ff9f65de"

FETCHSOURCE
Fetching storage object: gs://staging.your-project-id.appspot.com/your-project-id.default.20160326t100408#1458954328349000
Copying gs://staging.your-project-id.appspot.com/your-project-id.default.20160326t100408#1458954328349000...
Downloading file:///tmp/source-archive.tgz:                      13.32 KiB/13.32 KiB
FETCHBUILDER
Using default tag: latest
latest: Pulling from cloud-builders/dockerizer
bf61d14f65db: Pulling fs layer
3ea15286bc1a: Pulling fs layer
515285067dbf: Pulling fs layer
5e89b839ecfa: Pulling fs layer
e63e5abf57a3: Pulling fs layer
ec858f8c1767: Pulling fs layer
51d0afdd2ff8: Pulling fs layer
415319aa0c90: Pulling fs layer
51d0afdd2ff8: Verifying Checksum
51d0afdd2ff8: Download complete
415319aa0c90: Verifying Checksum
415319aa0c90: Download complete
5e89b839ecfa: Verifying Checksum
5e89b839ecfa: Download complete
3ea15286bc1a: Verifying Checksum
3ea15286bc1a: Download complete
515285067dbf: Verifying Checksum
515285067dbf: Download complete
e63e5abf57a3: Verifying Checksum
e63e5abf57a3: Download complete
ec858f8c1767: Verifying Checksum
ec858f8c1767: Download complete
bf61d14f65db: Verifying Checksum
bf61d14f65db: Download complete
bf61d14f65db: Pull complete
3ea15286bc1a: Pull complete
515285067dbf: Pull complete
5e89b839ecfa: Pull complete
e63e5abf57a3: Pull complete
ec858f8c1767: Pull complete
51d0afdd2ff8: Pull complete
415319aa0c90: Pull complete
Digest: sha256:b80a8cc7ed504307717c7530e795b0c2dea1ff99957806e0785ae831309084ae
Status: Downloaded newer image for gcr.io/cloud-builders/dockerizer:latest
BUILD
Client:
 Version:      1.9.1
 API version:  1.21
 Go version:   go1.4.3
 Git commit:   a34a1d5
 Built:        Fri Nov 20 17:56:04 UTC 2015
 OS/Arch:      linux/amd64

Server:
 Version:      1.9.1
 API version:  1.21
 Go version:   go1.4.2
 Git commit:   a34a1d5
 Built:        Fri Nov 20 13:12:04 UTC 2015
 OS/Arch:      linux/amd64
Sending build context to Docker daemon 90.62 kB
Step 1 : FROM gcr.io/google_appengine/ruby
 ---> 3e6d0d6d0575
Step 2 : RUN cd /rbenv/plugins/ruby-build &&     git pull &&     rbenv install -s 2.2.4 &&     rbenv global 2.2.4 &&     gem install -q --no-rdoc --no-ri bundler --version 1.11.2 &&     gem install -q --no-rdoc --no-ri foreman --version 0.78.0
 ---> Running in 451faee44d37
Already up-to-date.
Successfully installed bundler-1.11.2
1 gem installed
Successfully installed foreman-0.78.0
1 gem installed
 ---> 5da2526068cb
Removing intermediate container 451faee44d37
Step 3 : ENV RBENV_VERSION 2.2.4
 ---> Running in 1e6f8d74782b
 ---> 416110028d7d
Removing intermediate container 1e6f8d74782b
Step 4 : COPY Gemfile Gemfile.lock /app/
 ---> 0ab134d54690
Removing intermediate container 7337fb40c45b
Step 5 : RUN bundle install && rbenv rehash
 ---> Running in 0c258ea5a1be
Don't run Bundler as root. Bundler can ask for sudo if it is needed, and
installing your bundle as root will break this application for all non-root
users on this machine.
Fetching gem metadata from https://rubygems.org/...........
Fetching version metadata from https://rubygems.org/...
Fetching dependency metadata from https://rubygems.org/..
Using rake 10.4.2
Installing i18n 0.7.0
Installing json 1.8.3 with native extensions
Installing minitest 5.7.0
Installing thread_safe 0.3.5
Installing builder 3.2.2
Installing erubis 2.7.0
Installing mini_portile 0.6.2
Installing rack 1.6.4
Installing mime-types 2.6.1
Installing arel 6.0.0
Installing cliver 0.3.2
Installing diff-lcs 1.2.5
Installing multi_json 1.11.2
Installing websocket-extensions 0.1.2
Using bundler 1.11.2
Using thor 0.19.1
Installing rspec-support 3.3.0
Installing tzinfo 1.2.2
Installing nokogiri 1.6.6.2 with native extensions
Installing rack-test 0.6.3
Installing sprockets 3.2.0
Installing mail 2.6.3
Installing websocket-driver 0.6.3 with native extensions
Installing rspec-core 3.3.1
Installing rspec-expectations 3.3.0
Installing rspec-mocks 3.3.1
Installing activesupport 4.2.2
Installing tzinfo-data 1.2015.6
Installing loofah 2.0.2
Installing xpath 2.0.0
Installing rails-deprecated_sanitizer 1.0.3
Installing globalid 0.3.5
Installing activemodel 4.2.2
Installing rails-html-sanitizer 1.0.2
Installing capybara 2.4.4
Installing rails-dom-testing 1.0.6
Installing activejob 4.2.2
Installing activerecord 4.2.2
Installing poltergeist 1.8.1
Installing actionview 4.2.2
Installing actionpack 4.2.2
Installing actionmailer 4.2.2
Installing railties 4.2.2
Installing sprockets-rails 2.3.2
Installing rspec-rails 3.3.2
Installing rails 4.2.2
Bundle complete! 6 Gemfile dependencies, 47 gems now installed.
Use `bundle show [gemname]` to see where a bundled gem is installed.
 ---> 9fde5c5bec0c
Removing intermediate container 0c258ea5a1be
Step 6 : COPY . /app/
 ---> 05eb1e2b6b90
Removing intermediate container e885ebd8251c
Step 7 : ENTRYPOINT bundle exec rackup -p 8080 -E production config.ru
 ---> Running in 1b616e80361d
 ---> 0695731649da
Removing intermediate container 1b616e80361d
Successfully built 0695731649da
PUSH
The push refers to a repository [appengine.gcr.io/gcloud/your-project-id.default.20160326t100408] (len: 1)
Sending image list
Pushing repository appengine.gcr.io/gcloud/your-project-id.default.20160326t100408 (1 tags)
Image 3bc7cdb36864 already pushed, skipping
Image 4bfc20f0ed66 already pushed, skipping
Image ff52712bb308 already pushed, skipping
Image 5880acd9ad50 already pushed, skipping
Image 096d9403d234 already pushed, skipping
Image 956eb41cd003 already pushed, skipping
Image 01eaa1a367c4 already pushed, skipping
Image 943d779f0853 already pushed, skipping
Image 3cc9009b6572 already pushed, skipping
Image b19c39f03dbb already pushed, skipping
Image ca6428f24e68 already pushed, skipping
Image 7b90390ae965 already pushed, skipping
Image cb10a2abbe53 already pushed, skipping
Image 31bee42bdd8a already pushed, skipping
Image a04427afe410 already pushed, skipping
Image 8f70e181ae11 already pushed, skipping
Image 72b1839f75eb already pushed, skipping
Image 0ea63ea23bf2 already pushed, skipping
Image 86100fe6deed already pushed, skipping
Image 45ab69b78373 already pushed, skipping
Image 32066980c48e already pushed, skipping
Image fc85fe8bcbac already pushed, skipping
Image 76b185852e95 already pushed, skipping
Image eec69d4fcd9a already pushed, skipping
Image 17402d207077 already pushed, skipping
Image 27bea8c63202 already pushed, skipping
Image 3e6d0d6d0575 already pushed, skipping
5da2526068cb: Pushing
5da2526068cb: Image successfully pushed
416110028d7d: Pushing
416110028d7d: Image successfully pushed
0ab134d54690: Pushing
0ab134d54690: Image successfully pushed
9fde5c5bec0c: Pushing
9fde5c5bec0c: Image successfully pushed
05eb1e2b6b90: Pushing
05eb1e2b6b90: Image successfully pushed
0695731649da: Pushing
0695731649da: Image successfully pushed
Pushing tag for rev [0695731649da] on {https://appengine.gcr.io/v1/repositories/gcloud/your-project-id.default.20160326t100408/tags/latest}
DONE
----------------------------------------------------------------------------------------

Updating module [default]...done.
Deployed module [default] to [https://your-project-id.appspot.com]

app.yml

# [START runtime]
runtime: ruby
vm: true
entrypoint: bundle exec rackup -p 8080 -E production config.ru
# [END runtime]

# [START resources]
resources:
  cpu: .5
  memory_gb: 1.3
  disk_size_gb: 10
# [END resources]

# [START scaling]
automatic_scaling:
  min_num_instances: 1
  max_num_instances: 5
  cool_down_period_sec: 60
  cpu_utilization:
    target_utilization: 0.5
# [END scaling]

runtimeの設定がrubyプロジェクトに共通の設定でresources, scalingは環境に合わせて適宜チューニングしてください。デフォルトの状態としてはミニマルな設定になっているようです。

前提

手順

プロジェクトセットアップ

gcloud セットアップ

デプロイ時のログ

app.yml

参考