Add documentation for dependency proxy feature

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

doc/administration/dependency_proxy.md

+# GitLab Dependency Proxy administration **[PREMIUM ONLY]**
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ee/issues/7934) in [GitLab Premium](https://about.gitlab.com/pricing) 11.11.
+
+GitLab can be utilized as a dependency proxy for a variety of common package managers.
+
+This is the administration documentation. If you want to learn how to use the
+dependency proxies, see the [user guide](../user/group/dependency_proxy/index.md).
+
+## Enabling the Dependency Proxy feature
+
+NOTE: **Note:**
+Dependency proxy requires the Puma web server to be enabled.
+Puma support is EXPERIMENTAL at this time.
+
+To enable the Dependency proxy feature:
+
+**Omnibus GitLab installations**
+
+1. Edit `/etc/gitlab/gitlab.rb` and add the following line:
+
+   ```ruby
+   gitlab_rails['dependency_proxy_enabled'] = true
+   ```
+
+1. Save the file and [reconfigure GitLab][] for the changes to take effect.
+1. Enable the [Puma web server](https://docs.gitlab.com/omnibus/settings/puma.html).
+
+**Installations from source**
+
+1. After the installation is complete, you will have to configure the `dependency_proxy`
+   section in `config/gitlab.yml`. Set to `true` to enable it:
+
+   ```yaml
+   dependency_proxy:
+     enabled: true
+   ```
+
+1. [Restart GitLab] for the changes to take effect.
+1. Enable the [Puma web server](../install/installation.md#using-puma).
+
+## Changing the storage path
+
+By default, the dependency proxy files are stored locally, but you can change the default
+local location or even use object storage.
+
+### Changing the local storage path
+
+The dependency proxy files for Omnibus GitLab installations are stored under
+`/var/opt/gitlab/gitlab-rails/shared/dependency_proxy/` and for source
+installations under `shared/dependency_proxy/` (relative to the git home directory).
+To change the local storage path:
+
+**Omnibus GitLab installations**
+
+1. Edit `/etc/gitlab/gitlab.rb` and add the following line:
+
+   ```ruby
+   gitlab_rails['dependency_proxy_storage_path'] = "/mnt/dependency_proxy"
+   ```
+
+1. Save the file and [reconfigure GitLab][] for the changes to take effect.
+
+**Installations from source**
+
+1. Edit the `dependency_proxy` section in `config/gitlab.yml`:
+
+   ```yaml
+   dependency_proxy:
+     enabled: true
+     storage_path: shared/dependency_proxy
+   ```
+1. [Restart GitLab] for the changes to take effect.
+
+### Using object storage
+
+Instead of relying on the local storage, you can use an object storage to
+upload the blobs of the dependency proxy:
+
+**Omnibus GitLab installations**
+
+1. Edit `/etc/gitlab/gitlab.rb` and add the following lines (uncomment where
+   necessary):
+
+   ```ruby
+   gitlab_rails['dependency_proxy_enabled'] = true
+   gitlab_rails['dependency_proxy_storage_path'] = "/var/opt/gitlab/gitlab-rails/shared/dependency_proxy"
+   gitlab_rails['dependency_proxy_object_store_enabled'] = true
+   gitlab_rails['dependency_proxy_object_store_remote_directory'] = "dependency_proxy" # The bucket name.
+   gitlab_rails['dependency_proxy_object_store_direct_upload'] = false         # Use Object Storage directly for uploads instead of background uploads if enabled (Default: false).
+   gitlab_rails['dependency_proxy_object_store_background_upload'] = true      # Temporary option to limit automatic upload (Default: true).
+   gitlab_rails['dependency_proxy_object_store_proxy_download'] = false        # Passthrough all downloads via GitLab instead of using Redirects to Object Storage.
+   gitlab_rails['dependency_proxy_object_store_connection'] = {
+     ##
+     ## If the provider is AWS S3, uncomment the following
+     ##
+     #'provider' => 'AWS',
+     #'region' => 'eu-west-1',
+     #'aws_access_key_id' => 'AWS_ACCESS_KEY_ID',
+     #'aws_secret_access_key' => 'AWS_SECRET_ACCESS_KEY',
+     ##
+     ## If the provider is other than AWS (an S3-compatible one), uncomment the following
+     ##
+     #'host' => 's3.amazonaws.com',
+     #'aws_signature_version' => 4             # For creation of signed URLs. Set to 2 if provider does not support v4.
+     #'endpoint' => 'https://s3.amazonaws.com' # Useful for S3-compliant services such as DigitalOcean Spaces.
+     #'path_style' => false                    # If true, use 'host/bucket_name/object' instead of 'bucket_name.host/object'.
+   }
+   ```
+
+1. Save the file and [reconfigure GitLab][] for the changes to take effect.
+
+**Installations from source**
+
+1. Edit the `dependency_proxy` section in `config/gitlab.yml` (uncomment where necessary):
+
+   ```yaml
+   dependency_proxy:
+     enabled: true
+     ##
+     ## The location where build dependency_proxy are stored (default: shared/dependency_proxy).
+     ##
+     #storage_path: shared/dependency_proxy
+     object_store:
+       enabled: false
+       remote_directory: dependency_proxy # The bucket name.
+       #direct_upload: false      # Use Object Storage directly for uploads instead of background uploads if enabled (Default: false).
+       #background_upload: true   # Temporary option to limit automatic upload (Default: true).
+       #proxy_download: false     # Passthrough all downloads via GitLab instead of using Redirects to Object Storage.
+       connection:
+         ##
+         ## If the provider is AWS S3, uncomment the following
+         ##
+         #provider: AWS
+         #region: us-east-1
+         #aws_access_key_id: AWS_ACCESS_KEY_ID
+         #aws_secret_access_key: AWS_SECRET_ACCESS_KEY
+         ##
+         ## If the provider is other than AWS (an S3-compatible one), uncomment the following
+         ##
+         #host: 's3.amazonaws.com'             # default: s3.amazonaws.com.
+         #aws_signature_version: 4             # For creation of signed URLs. Set to 2 if provider does not support v4.
+         #endpoint: 'https://s3.amazonaws.com' # Useful for S3-compliant services such as DigitalOcean Spaces.
+         #path_style: false                    # If true, use 'host/bucket_name/object' instead of 'bucket_name.host/object'.
+   ```
+
+1. [Restart GitLab] for the changes to take effect.
+
+[reconfigure gitlab]: restart_gitlab.md#omnibus-gitlab-reconfigure "How to reconfigure Omnibus GitLab"
+[restart gitlab]: restart_gitlab.md#omnibus-gitlab-reconfigure "How to reconfigure Omnibus GitLab"

doc/user/group/dependency_proxy/index.md

+# Dependency Proxy **[PREMIUM]**
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ee/issues/7934) in [GitLab Premium](https://about.gitlab.com/pricing/) 11.11.
+
+NOTE: **Note:**
+This is the user guide. In order to use the dependency proxy, an administrator
+must first [configure it](../../../administration/dependency_proxy.md).
+
+For many organizations, it is desirable to have a local proxy for frequently used
+upstream images/packages. In the case of CI/CD, the proxy is responsible for
+receiving a request and returning the upstream image from a registry, acting
+as a pull-through cache.
+
+The dependency proxy is available in the group level. To access it, navigate to
+a group's **Overview > Dependency Proxy**.
+
+![Dependency Proxy group page](img/group_dependency_proxy.png)
+
+## Supported dependency proxies
+
+NOTE: **Note:**
+For a list of the upcoming additions to the proxies, visit the
+[direction page](https://about.gitlab.com/direction/package/dependency_proxy/#top-vision-items).
+
+The following dependency proxies are supported.
+
+| Dependency proxy | GitLab version |
+| ---------------- | -------------- |
+| Docker           | 11.11+         |
+
+## Using the Docker dependency proxy
+
+With the Docker dependency proxy, you can use GitLab as a source for a Docker image.
+To get a Docker image into the dependency proxy:
+
+1. Find the proxy URL on your group's page under **Overview > Dependency Proxy**,
+   for example `gitlab.com/groupname/dependency_proxy/containers`.
+1. Trigger GitLab to pull the Docker image you want (e.g., `alpine:latest` or
+   `linuxserver/nextcloud:latest`) and store it in the proxy storage by using
+   one of the following ways:
+
+   - Manually pulling the Docker image:
+
+     ```bash
+     docker pull gitlab.com/groupname/dependency_proxy/containers/alpine:latest
+     ```
+
+   - From a `Dockerfile`:
+
+     ```bash
+     FROM gitlab.com/groupname/dependency_proxy/containers/alpine:latest
+     ```
+
+   - In [`.gitlab-ci.yml`](../../../ci/yaml/README.md#image):
+
+     ```bash
+     image: gitlab.com/groupname/dependency_proxy/containers/alpine:latest
+     ```
+
+GitLab will then pull the Docker image from Docker Hub and will cache the blobs
+on the GitLab server. The next time you pull the same image, it will get the latest
+information about the image from Docker Hub but will serve the existing blobs
+from GitLab.
+
+The blobs are kept forever, and there is no hard limit on how much data can be
+stored.
+
+## Limitations
+
+The following limitations apply:
+
+- Only public groups are supported (authentication is not supported yet).
+- Only Docker Hub is supported.
+- This feature requires Docker Hub being available.

doc/user/group/index.md

@@ -368,5 +368,9 @@ and issues) performed by your group members.
 
 With [GitLab Issues Analytics](issues_analytics/index.md), in groups, you can see a bar chart of the number of issues created each month.
 
+## Dependency Proxy **[PREMIUM]**
+
+Use GitLab as a [dependency proxy](dependency_proxy/index.md) for upstream Docker images.
+
 [ee]: https://about.gitlab.com/pricing/
 [ee-2534]: https://gitlab.com/gitlab-org/gitlab-ee/issues/2534