Merge branch 'registry-example' into 'master'

Update CI Docker docs

## What does this MR do?

Updates documentation with:

* instructions for bind-mounting for docker runners (fixes #17769 and #13898)
* examples of using the GitLab Container Registry in docker-based builds (fixes #17968 and #17967)
* update runner instructions for `gitlab-ci-multi-runner` (fixes https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/1337)
* some grammar fixes

## Are there points in the code the reviewer needs to double check?

The markdown in general. The runner commands. I haven't been able to verify the socket version works yet.

## Why was this MR needed?

Better documentation for users.

## What are the relevant issue numbers?
#17769, #13898, #17968, #17967 

## Screenshots (if relevant)

See merge request !4524

5 files changed, 201 insertions, 58 deletions

diff --git a/doc/ci/docker/using_docker_build.md b/doc/ci/docker/using_docker_build.md
index ca52a483a59..7f83f846454 100644
--- a/doc/ci/docker/using_docker_build.md
+++ b/doc/ci/docker/using_docker_build.md
@@ -4,14 +4,14 @@ GitLab CI allows you to use Docker Engine to build and test docker-based project
 
 **This also allows to you to use `docker-compose` and other docker-enabled tools.**
 
-This is one of new trends in Continuous Integration/Deployment to:
+One of the new trends in Continuous Integration/Deployment is to:
 
-1. create application image,
-1. run test against created image,
-1. push image to remote registry,
-1. deploy server from pushed image
+1. create an application image,
+1. run tests against the created image,
+1. push image to a remote registry, and
+1. deploy to a server from the pushed image.
 
-It's also useful in case when your application already has the `Dockerfile` that can be used to create and test image:
+It's also useful when your application already has the `Dockerfile` that can be used to create and test an image:
 ```bash
 $ docker build -t my-image dockerfiles/
 $ docker run my-docker-image /script/to/run/tests
@@ -19,24 +19,25 @@ $ docker tag my-image my-registry:5000/my-image
 $ docker push my-registry:5000/my-image
 ```
 
-However, this requires special configuration of GitLab Runner to enable `docker` support during build.
-**This requires running GitLab Runner in privileged mode which can be harmful when untrusted code is run.**
+This requires special configuration of GitLab Runner to enable `docker` support during builds.
 
-There are two methods to enable the use of `docker build` and `docker run` during build.
+## Runner Configuration
 
-## 1. Use shell executor
+There are three methods to enable the use of `docker build` and `docker run` during builds; each with their own tradeoffs.
+
+### Use shell executor
 
 The simplest approach is to install GitLab Runner in `shell` execution mode.
-GitLab Runner then executes build scripts as `gitlab-runner` user.
+GitLab Runner then executes build scripts as the `gitlab-runner` user.
 
 1. Install [GitLab Runner](https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/#installation).
 
 1. During GitLab Runner installation select `shell` as method of executing build scripts or use command:
 
     ```bash
-    $ sudo gitlab-runner register -n \
+    $ sudo gitlab-ci-multi-runner register -n \
       --url https://gitlab.com/ci \
-      --token RUNNER_TOKEN \
+      --registration-token REGISTRATION_TOKEN \
       --executor shell
       --description "My Runner"
     ```
@@ -70,16 +71,18 @@ GitLab Runner then executes build scripts as `gitlab-runner` user.
 
 5. You can now use `docker` command and install `docker-compose` if needed.
 
-6. However, by adding `gitlab-runner` to `docker` group you are effectively granting `gitlab-runner` full root permissions.
-For more information please checkout [On Docker security: `docker` group considered harmful](https://www.andreas-jung.com/contents/on-docker-security-docker-group-considered-harmful).
+> **Note:**
+* By adding `gitlab-runner` to the `docker` group you are effectively granting `gitlab-runner` full root permissions.
+For more information please read [On Docker security: `docker` group considered harmful](https://www.andreas-jung.com/contents/on-docker-security-docker-group-considered-harmful).
 
-## 2. Use docker-in-docker executor
+### Use docker-in-docker executor
 
-The second approach is to use the special Docker image with all tools installed
+The second approach is to use the special docker-in-docker (dind)
+[Docker image](https://hub.docker.com/_/docker/) with all tools installed
 (`docker` and `docker-compose`) and run the build script in context of that
 image in privileged mode.
 
-In order to do that follow the steps:
+In order to do that, follow the steps:
 
 1. Install [GitLab Runner](https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/#installation).
 
@@ -87,9 +90,9 @@ In order to do that follow the steps:
    mode:
 
     ```bash
-    sudo gitlab-runner register -n \
+    sudo gitlab-ci-multi-runner register -n \
       --url https://gitlab.com/ci \
-      --token RUNNER_TOKEN \
+      --registration-token REGISTRATION_TOKEN \
       --executor docker \
       --description "My Docker Runner" \
       --docker-image "docker:latest" \
@@ -119,11 +122,7 @@ In order to do that follow the steps:
         Insecure = false
     ```
 
-    If you want to use the Shared Runners available on your GitLab CE/EE
-    installation in order to build Docker images, then make sure that your
-    Shared Runners configuration has the `privileged` mode set to `true`.
-
-1. You can now use `docker` from build script:
+1. You can now use `docker` in the build script (note the inclusion of the `docker:dind` service):
 
     ```yaml
     image: docker:latest
@@ -141,14 +140,177 @@ In order to do that follow the steps:
       - docker run my-docker-image /script/to/run/tests
     ```
 
-1. However, by enabling `--docker-privileged` you are effectively disabling all
-   the security mechanisms of containers and exposing your host to privilege
-   escalation which can lead to container breakout.
-
-   For more information, check out the official Docker documentation on
-   [Runtime privilege and Linux capabilities][docker-cap].
+Docker-in-Docker works well, and is the recommended configuration, but it is not without its own challenges:
+* By enabling `--docker-privileged`, you are effectively disabling all of
+the security mechanisms of containers and exposing your host to privilege
+escalation which can lead to container breakout. For more information, check out the official Docker documentation on
+[Runtime privilege and Linux capabilities][docker-cap].
+* Using docker-in-docker, each build is in a clean environment without the past
+history. Concurrent builds work fine because every build gets it's own instance of docker engine so they won't conflict with each other. But this also means builds can be slower because there's no caching of layers.
+* By default, `docker:dind` uses `--storage-driver vfs` which is the slowest form
+offered.
 
 An example project using this approach can be found here: https://gitlab.com/gitlab-examples/docker.
 
+### Use Docker socket binding
+
+The third approach is to bind-mount `/var/run/docker.sock` into the container so that docker is available in the context of that image.
+
+In order to do that, follow the steps:
+
+1. Install [GitLab Runner](https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/#installation).
+
+1. Register GitLab Runner from the command line to use `docker` and share `/var/run/docker.sock`:
+
+    ```bash
+    sudo gitlab-ci-multi-runner register -n \
+      --url https://gitlab.com/ci \
+      --registration-token REGISTRATION_TOKEN \
+      --executor docker \
+      --description "My Docker Runner" \
+      --docker-image "docker:latest" \
+      --docker-volumes /var/run/docker.sock:/var/run/docker.sock
+    ```
+
+    The above command will register a new Runner to use the special
+    `docker:latest` image which is provided by Docker. **Notice that it's using
+    the Docker daemon of the Runner itself, and any containers spawned by docker commands will be siblings of the Runner rather than children of the runner.** This may have complications and limitations that are unsuitable for your workflow.
+
+    The above command will create a `config.toml` entry similar to this:
+
+    ```
+    [[runners]]
+      url = "https://gitlab.com/ci"
+      token = REGISTRATION_TOKEN
+      executor = "docker"
+      [runners.docker]
+        tls_verify = false
+        image = "docker:latest"
+        privileged = false
+        disable_cache = false
+        volumes = ["/var/run/docker.sock", "/cache"]
+      [runners.cache]
+        Insecure = false
+    ```
+
+1. You can now use `docker` in the build script (note that you don't need to include the `docker:dind` service as when using the Docker in Docker executor):
+
+    ```yaml
+    image: docker:latest
+
+    before_script:
+    - docker info
+
+    build:
+      stage: build
+      script:
+      - docker build -t my-docker-image .
+      - docker run my-docker-image /script/to/run/tests
+    ```
+
+While the above method avoids using Docker in privileged mode, you should be aware of the following implications:
+* By sharing the docker daemon, you are effectively disabling all
+the security mechanisms of containers and exposing your host to privilege
+escalation which can lead to container breakout. For example, if a project
+ran `docker rm -f $(docker ps -a -q)` it would remove the GitLab Runner
+containers.
+* Concurrent builds may not work; if your tests
+create containers with specific names, they may conflict with each other.
+* Sharing files and directories from the source repo into containers may not
+work as expected since volume mounting is done in the context of the host
+machine, not the build container.
+e.g. `docker run --rm -t -i -v $(pwd)/src:/home/app/src test-image:latest run_app_tests`
+
+## Using the GitLab Container Registry
+
+> **Note:**
+This feature requires GitLab 8.8 and GitLab Runner 1.2.
+
+Once you've built a Docker image, you can push it up to the built-in [GitLab Container Registry](../../container_registry/README.md). For example, if you're using
+docker-in-docker on your runners, this is how your `.gitlab-ci.yml` could look:
+
+
+```yaml
+ build:
+   image: docker:latest
+   services:
+   - docker:dind
+   stage: build
+   script:
+     - docker login -u gitlab-ci-token -p $CI_BUILD_TOKEN registry.example.com
+     - docker build -t registry.example.com/group/project:latest .
+     - docker push registry.example.com/group/project:latest
+```
+
+You have to use the credentials of the special `gitlab-ci-token` user with its
+password stored in `$CI_BUILD_TOKEN` in order to push to the Registry connected
+to your project. This allows you to automate building and deployment of your
+Docker images.
+
+Here's a more elaborate example that splits up the tasks into 4 pipeline stages,
+including two tests that run in parallel. The build is stored in the container
+registry and used by subsequent stages, downloading the image
+when needed. Changes to `master` also get tagged as `latest` and deployed using
+an application-specific deploy script:
+
+```yaml
+image: docker:latest
+services:
+- docker:dind
+
+stages:
+- build
+- test
+- release
+- deploy
+
+variables:
+  CONTAINER_TEST_IMAGE: registry.example.com/my-group/my-project:$CI_BUILD_REF_NAME
+  CONTAINER_RELEASE_IMAGE: registry.example.com/my-group/my-project:latest
+
+before_script:
+  - docker login -u gitlab-ci-token -p $CI_BUILD_TOKEN registry.example.com
+
+build:
+  stage: build
+  script:
+    - docker build --pull -t $CONTAINER_TEST_IMAGE .
+    - docker push $CONTAINER_TEST_IMAGE
+
+test1:
+  stage: test
+  script:
+    - docker pull $CONTAINER_TEST_IMAGE
+    - docker run $CONTAINER_TEST_IMAGE /script/to/run/tests
+
+test2:
+  stage: test
+  script:
+    - docker pull $CONTAINER_TEST_IMAGE
+    - docker run $CONTAINER_TEST_IMAGE /script/to/run/another/test
+
+release-image:
+  stage: release
+  script:
+    - docker pull $CONTAINER_TEST_IMAGE
+    - docker tag $CONTAINER_TEST_IMAGE $CONTAINER_RELEASE_IMAGE
+    - docker push $CONTAINER_RELEASE_IMAGE
+  only:
+    - master
+
+deploy:
+  stage: deploy
+  script:
+    - ./deploy.sh
+  only:
+    - master
+```
+
+Some things you should be aware of when using the Container Registry:
+* You must log in to the container registry before running commands. Putting this in `before_script` will run it before each build job.
+* Using `docker build --pull` makes sure that Docker fetches any changes to base images before building just in case your cache is stale. It takes slightly longer, but means you don’t get stuck without security patches to base images.
+* Doing an explicit `docker pull` before each `docker run` makes sure to fetch the latest image that was just built. This is especially important if you are using multiple runners that cache images locally. Using the git SHA in your image tag makes this less necessary since each build will be unique and you shouldn't ever have a stale image, but it's still possible if you re-build a given commit after a dependency has changed.
+* You don't want to build directly to `latest` in case there are multiple builds happening simultaneously.
+
 [docker-in-docker]: https://blog.docker.com/2013/09/docker-can-now-run-within-docker/
 [docker-cap]: https://docs.docker.com/engine/reference/run/#runtime-privilege-and-linux-capabilities
diff --git a/doc/ci/docker/using_docker_images.md b/doc/ci/docker/using_docker_images.md
index 56ac2195c49..a849905ac6b 100644
--- a/doc/ci/docker/using_docker_images.md
+++ b/doc/ci/docker/using_docker_images.md
@@ -23,7 +23,7 @@ To use GitLab Runner with docker you need to register a new runner to use the
 `docker` executor:
 
 ```bash
-gitlab-runner register \
+gitlab-ci-multi-runner register \
   --url "https://gitlab.com/" \
   --registration-token "PROJECT_REGISTRATION_TOKEN" \
   --description "docker-ruby-2.1" \
diff --git a/doc/ci/examples/php.md b/doc/ci/examples/php.md
index 26953014502..17e1c64bb8a 100644
--- a/doc/ci/examples/php.md
+++ b/doc/ci/examples/php.md
@@ -263,10 +263,10 @@ terminal execute:
 
 ```bash
 # Check using docker executor
-gitlab-runner exec docker test:app
+gitlab-ci-multi-runner exec docker test:app
 
 # Check using shell executor
-gitlab-runner exec shell test:app
+gitlab-ci-multi-runner exec shell test:app
 ```
 
 ## Example project
diff --git a/doc/ci/runners/README.md b/doc/ci/runners/README.md
index b42d7a62ebc..400784da617 100644
--- a/doc/ci/runners/README.md
+++ b/doc/ci/runners/README.md
@@ -63,10 +63,10 @@ instance.
 Now simply register the runner as any runner:
 
 ```
-sudo gitlab-runner register
+sudo gitlab-ci-multi-runner register
 ```
 
-Shared runners are enabled by default as of GitLab 8.2, but can be disabled with the 
+Shared runners are enabled by default as of GitLab 8.2, but can be disabled with the
 `DISABLE SHARED RUNNERS` button. Previous versions of GitLab defaulted shared runners to
 disabled.
 
@@ -93,7 +93,7 @@ setup a specific runner for this project.
 To register the runner, run the command below and follow instructions:
 
 ```
-sudo gitlab-runner register
+sudo gitlab-ci-multi-runner register
 ```
 
 ###  Making an existing Shared Runner Specific
diff --git a/doc/container_registry/README.md b/doc/container_registry/README.md
index 4df24ef13cc..1b465434498 100644
--- a/doc/container_registry/README.md
+++ b/doc/container_registry/README.md
@@ -79,27 +79,8 @@ delete them.
 This feature requires GitLab 8.8 and GitLab Runner 1.2.
 
 Make sure that your GitLab Runner is configured to allow building docker images.
-You have to check the [Using Docker Build documentation](../../ci/docker/using_docker_build.md).
-
-You can use [docker:dind](https://hub.docker.com/_/docker/) to build your images,
-and this is how `.gitlab-ci.yml` should look like:
-
-```
- build_image:
-   image: docker:git
-   services:
-   - docker:dind
-   stage: build
-   script:
-     - docker login -u gitlab-ci-token -p $CI_BUILD_TOKEN registry.example.com
-     - docker build -t registry.example.com/group/project:latest .
-     - docker push registry.example.com/group/project:latest
-```
-
-You have to use the credentials of the special `gitlab-ci-token` user with its
-password stored in `$CI_BUILD_TOKEN` in order to push to the Registry connected
-to your project. This allows you to automated building and deployment of your
-Docker images.
+You have to check the [Using Docker Build documentation](../ci/docker/using_docker_build.md).
+Then see the CI documentation on [Using the GitLab Container Registry](../ci/docker/using_docker_build.md#using-the-gitlab-container-registry).
 
 ## Limitations