Put back proxy server content (docker#5951)

Author: Misty Stanley-Jones

_data/toc.yaml

@@ -271,6 +271,8 @@ guides:
         title: Docker and iptables
       - path: /config/containers/container-networking/
         title: Container networking
+      - path: /network/proxy/
+        title: Configure Docker to use a proxy server
     - sectiontitle: Legacy networking content
       section:
       - path: /network/links/

config/containers/container-networking.md

@@ -63,3 +63,8 @@ settings on a per-container basis.
 | `--dns-search` | A DNS search domain to search non-fully-qualified hostnames. To specify multiple DNS search prefixes, use multiple `--dns-search` flags.                                                                                                                            |
 | `--dns-opt`    | A key-value pair representing a DNS option and its value. See your operating system's documentation for `resolv.conf` for valid options.                                                                                                                            |
 | `--hostname`   | The hostname a container uses for itself. Defaults to the container's name if not specified.                                                                                                                                                                        |
+
+## Proxy server
+
+If your container needs to use a proxy server, see
+[Use a proxy server](/network/proxy.md).

network/proxy.md

@@ -0,0 +1,67 @@
+---
+title: Configure Docker to use a proxy server
+description: How to configure the Docker client to use a proxy server
+keywords: network, networking, proxy, client
+---
+
+If your container needs to use an HTTP, HTTPS, or FTP proxy server, you can
+configure it in different ways:
+
+- In Docker 17.07 and higher, you can
+  [configure the Docker client](#configure-the-docker-client) to pass
+  proxy information to containers automatically.
+
+- In Docker 17.06 and lower, you must
+  [set appropriate environment variables](#use-environment-variables)
+  within the container. You can do this when you build the image (which makes
+  the image less portable) or when you create or run the container.
+
+## Configure the Docker client
+
+1.  On the Docker client, create or edit the file `~/.docker/config.json` in the
+    home directory of the user which starts containers. Add JSON such as the
+    following, substituting the type of proxy with `httpsProxy` or `ftpProxy` if
+    necessary, and substituting the address and port of the proxy server. You
+    can configure multiple proxy servers at the same time.
+
+    You can optionally exclude hosts or ranges from going through the proxy
+    server by setting a `noProxy` key to one or more comma-separated IP
+    addresses or hosts. Using the `*` character as a wildcard is supported, as
+    shown in this example.
+
+    ```json
+    {
+     "proxies":
+     {
+       "default":
+       {
+         "httpProxy": "http://127.0.0.1:3001",
+         "noProxy": "*.test.example.com,.example2.com"
+       }
+     }
+    }
+    ```
+
+    Save the file.
+
+ 2. When you create or start new containers, the environment variables are
+    set automatically within the container.
+
+
+## Use environment variables
+
+### Set the environment variables manually
+
+When you build the image, or using the `--env` flag when you create or run the
+container, you can set one or more of the following variables to the appropriate
+value. This method makes the image less portable, so if you have Docker 17.07
+or higher, you should [configure the Docker client](#configure-the-docker-client)
+instead.
+
+| Variable      | Dockerfile example                                | `docker run` Example                                |
+|:--------------|:--------------------------------------------------|:----------------------------------------------------|
+| `HTTP_PROXY`  | `ENV HTTP_PROXY "http://127.0.0.1:3001"`          | `--env HTTP_PROXY "http://127.0.0.1:3001"`          |
+| `HTTPS_PROXY` | `ENV HTTPS_PROXY "https://127.0.0.1:3001"`        | `--env HTTPS_PROXY "https://127.0.0.1:3001"`        |
+| `FTP_PROXY`   | `ENV FTP_PROXY "ftp://127.0.0.1:3001"`            | `--env FTP_PROXY "ftp://127.0.0.1:3001"`            |
+| `NO_PROXY`    | `ENV NO_PROXY "*.test.example.com,.example2.com"` | `--env NO_PROXY "*.test.example.com,.example2.com"` |
+