Docs - Add more info about using NFS with a firewall

doc/administration/high_availability/nfs_host_client_setup.md

@@ -12,24 +12,24 @@ and Corosync](http://clusterlabs.org/) for highly available NFS in production.
 Below are instructions for setting up an application node(client) in an HA cluster
 to read from and write to a central NFS server(host).
 
-
 ## NFS Server Setup
+
 > Follow the instructions below to set up and configure your NFS server.
 
-#### Step 1 - Install NFS Server on Host
+### Step 1 - Install NFS Server on Host
 
 Installing the nfs-kernel-server package allows you to share directories with the clients running the GitLab application.
 
-```
-$ apt-get update
-$ apt-get install nfs-kernel-server
+```sh
+apt-get update
+apt-get install nfs-kernel-server
 ```
 
-#### Step 2 - Export Host's Home Directory to Client
+### Step 2 - Export Host's Home Directory to Client
 
 In this setup we will share the home directory on the host with the client. Edit the exports file as below to share the host's home directory with the client. If you have multiple clients running GitLab you must enter the client IP addresses in line in the `/etc/exports` file.
 
-```
+```text
 #/etc/exports for one client
 /home <client-ip-address>(rw,sync,no_root_squash,no_subtree_check)
 
@@ -39,67 +39,63 @@ In this setup we will share the home directory on the host with the client. Edit
 
 Restart the NFS server after making changes to the `exports` file for the changes 
 to take effect.
-```
-$ systemctl restart nfs-kernel-server
-```
-
-Check that traffic from the client is allowed by the firewall on the host by running 
-the command: `sudo ufw status`. If blocked you can allow traffic from between a specific 
-client with the command below.
 
-```
-$ sudo ufw allow from <client-ip-address> to any port nfs
+```sh
+systemctl restart nfs-kernel-server
 ```
 
-
+NOTE: **Note:**
+You may need to update your server's firewall. See the [firewall section](#nfs-in-a-firewalled-environment) at the end of this guide.
 
 ## Client/ GitLab application node Setup
+
 > Follow the instructions below to connect any GitLab rails application node running
 inside your HA environment to the NFS server configured above.
 
-#### Step 1 - Install NFS Common on Client
+### Step 1 - Install NFS Common on Client
 
 The nfs-common provides NFS functionality without installing server components which 
 we don't need running on the application nodes.
 
+```sh
+apt-get update
+apt-get install nfs-common
 ```
-$ apt-get update
-$ apt-get install nfs-common
-```
-
 
-#### Step 2 - Create Mount Points on Client
+### Step 2 - Create Mount Points on Client
 
 Create a directroy on the client that we can mount the shared directory from the host. 
 Please note that if your mount point directory contains any files they will be hidden
 once the remote shares are mounted. An empty/new directory on the client is recommended
 for this purpose.
-```
-$ mkdir -p /nfs/home
+
+```sh
+mkdir -p /nfs/home
 ```
 
 Confirm that the mount point works by mounting it on the client and checking that
 it is mounted with the command below:
 
-```
-$ mount <host_ip_address>:/home
-$ df -h
+```sh
+mount <host_ip_address>:/home
+df -h
 ```
 
-#### Step 3 - Set up Automatic Mounts on Boot
+### Step 3 - Set up Automatic Mounts on Boot
 
 Edit `/etc/fstab` on client as below to mount the remote shares automatically at boot. 
 Note that GitLab requires advisory file locking, which is only supported natively in
 NFS version 4. NFSv3 also supports locking as long as Linux Kernel 2.6.5+ is used.
 We recommend using version 4 and do not specifically test NFSv3.
 
-```
+```text
 #/etc/fstab
 165.227.159.85:/home       /nfs/home      nfs4 defaults,soft,rsize=1048576,wsize=1048576,noatime,nofail,lookupcache=positive 0 2
 ```
+
 Reboot the client and confirm that the mount point is mounted automatically.
 
-#### Step 4 - Set up GitLab to Use NFS mounts
+### Step 4 - Set up GitLab to Use NFS mounts
 
 When using the default Omnibus configuration you will need to share 5 data locations
 between all GitLab cluster nodes. No other locations should be shared. Changing the
@@ -107,7 +103,7 @@ default file locations in `gitlab.rb` on the client allows you to have one main
 point and have all the required locations as subdirectories to use the NFS mount for
 git-data.
 
-```
+```text
 git_data_dirs({"default" => "/nfs/home/var/opt/gitlab-data/git-data"})
 user['home'] = '/nfs/home/var/opt/gitlab-data/home'
 gitlab_rails['uploads_directory'] = '/nfs/home/var/opt/gitlab-data/uploads'
@@ -116,3 +112,22 @@ gitlab_ci['builds_directory'] = '/nfs/home/var/opt/gitlab-data/builds'
 ```
 
 Save the changes in `gitlab.rb` and run `gitlab-ctl reconfigure`.
+
+## NFS in a Firewalled Environment
+
+If the traffic between your NFS server and NFS client(s) is subject to port filtering 
+by a firewall, then you will need to reconfigure that firewall to allow NFS communication.  
+
+[This guide from TDLP](http://tldp.org/HOWTO/NFS-HOWTO/security.html#FIREWALLS) 
+covers the basics of using NFS in a firewalled environment. Additionally, we encourage you to 
+search for and review the specific documentation for your OS/distro and your firewall software. 
+
+Example for Ubuntu:  
+
+Check that NFS traffic from the client is allowed by the firewall on the host by running 
+the command: `sudo ufw status`. If it's being blocked, then you can allow traffic from a specific 
+client with the command below.
+
+```sh
+sudo ufw allow from <client-ip-address> to any port nfs
+```