Merge pull request coreos#367 from endocode/kayrus/kubelet_wrapper

docs: Added an info about custom nameservers for the kubelet wrapper

Documentation/kubelet-wrapper.md

@@ -17,7 +17,7 @@ An example systemd kubelet.service file which takes advantage of the kubelet-wra
 
 **/etc/systemd/system/kubelet.service**
 
-```yaml
+```ini
 [Service]
 Environment=KUBELET_VERSION=v1.2.0_coreos.1
 ExecStart=/usr/lib/coreos/kubelet-wrapper \
@@ -27,21 +27,37 @@ ExecStart=/usr/lib/coreos/kubelet-wrapper \
 
 In the example above we set the `KUBELET_VERSION` and the kubelet-wrapper script takes care of running the correct container image with our desired API server address and manifest location.
 
+### Customizing rkt Options
+
+Passing customized options or flags to rkt can be accomplished with the RKT_OPTS environment variable. Referencing it in a unit file is straightforward. Example below mounts host's `/etc/resolv.conf` file directly into the container:
+
+```ini
+[Service]
+Environment=RKT_OPTS="--volume=resolv,kind=host,source=/etc/resolv.conf --mount volume=resolv,target=/etc/resolv.conf"
+Environment=KUBELET_VERSION=v1.2.0_coreos.1
+ExecStart=/usr/lib/coreos/kubelet-wrapper \
+  --api-servers=http://127.0.0.1:8080 \
+  --config=/etc/kubernetes/manifests
+```
+
 ## Manual deployment
 
 If you wish to use the kubelet-wrapper on a CoreOS version prior to 962.0.0, you can manually place the script on the host. Please note that this requires rkt version 0.15.0+.
 
 For example:
 
-- Retrieve a copy of the [kubelet-wrapper script](https://github.com/coreos/coreos-overlay/blob/master/app-admin/kubelet-wrapper/files/kubelet-wrapper)
+- Retrieve a copy of the [kubelet-wrapper script][kubelet-wrapper]
 - Place on the host: `/opt/bin/kubelet-wrapper`
 - Make the script executable: `chmod +x /opt/bin/kubelet-wrapper`
 - Reference from your kubelet service file:
 
-```yaml
+```ini
 [Service]
 Environment=KUBELET_VERSION=v1.2.0_coreos.1
 ExecStart=/opt/bin/kubelet-wrapper \
   --api-servers=http://127.0.0.1:8080 \
   --config=/etc/kubernetes/manifests
 ```
+
+[#2141]: https://github.com/coreos/rkt/issues/2141
+[kubelet-wrapper]: https://github.com/coreos/coreos-overlay/blob/master/app-admin/kubelet-wrapper/files/kubelet-wrapper