Add instructions for deploying Pixie to select nodes. (#185)

* Add instructions for deploying Pixie to select nodes.

Signed-off-by: Hannah Troisi <htroisi@pixielabs.ai>

* tweak

Signed-off-by: Hannah Troisi <htroisi@pixielabs.ai>

* address nserrino's comment

Signed-off-by: Hannah Troisi <htroisi@pixielabs.ai>

Author: htroisi

content/en/02-installing-pixie/01-requirements.md

@@ -64,7 +64,7 @@ Pixie requires an `x86-64` architecture.
 
 ## Operating System
 
-Pixie runs on Linux nodes only.
+Pixie runs on Linux nodes only. You can configure Pixie to [deploy to a subset of the nodes](/reference/admin/deploy-options#deploy-pixie-to-a-subset-of-nodes) in your cluster.
 
 |         | Support         | Version           |
 | :------ | :-------------  | :---------------- |

content/en/05-reference/01-admin/04-deploy-options.md

@@ -11,6 +11,7 @@ Pixie offers the following deploy options:
 
 - [Annotate Pixie's resources](#annotating-pixie's-resources)
 - [Label Pixie's resources](#labeling-pixie's-resources)
+- [Deploy to a subset of nodes](#deploy-pixie-to-a-subset-of-nodes)
 - [Provide a custom cluster name](#providing-a-custom-cluster-name)
 - [Configure Pixie's memory usage](#configuring-pixie's-memory-usage)
 - [Set the data access mode](#setting-the-data-access-mode)
@@ -54,6 +55,28 @@ To label Pixie's resources when deploying with [Helm](/installing-pixie/install-
 helm install pixie pixie-operator/pixie-operator-chart --set deployKey=<deploy-key-goes-here> --namespace pl --create-namespace --set labels=key1=value1,key2=value2
 ```
 
+## Deploy Pixie to a subset of nodes
+
+When deploying Pixie, you have the option of selecting which nodes Pixie will be deployed to in your cluster. For example, Pixie [runs on Linux nodes only](/installing-pixie/requirements/#operating-system), so you would use this option to deploy Pixie to clusters with mixed node types.
+
+To deploy Pixie to a subset of the nodes in your cluster:
+
+1. [Label the target nodes](https://kubernetes.io/docs/tasks/configure-pod-container/assign-pods-nodes/#add-a-label-to-a-node) with `pixie=allowed`.
+
+2. Add a [`nodeSelector`](https://kubernetes.io/docs/concepts/scheduling-eviction/assign-pod-node/#nodeselector) to Pixie's [`vizier-pem`](/reference/architecture/#vizier) datacollector pods during deployment:
+
+> When deploying with the [Pixie CLI](/installing-pixie/install-schemes/cli/), use the `--patches` flag:
+
+```bash
+px deploy --patches='vizier-pem:{\"spec\":{\"template\":{\"spec\":{\"nodeSelector\":{\"pixie\": \"allowed\"}}}}}'
+```
+
+> When deploying with [Helm](/installing-pixie/install-schemes/helm/), use the `patches.vizier-pem` field:
+
+```bash
+helm install pixie pixie-operator/pixie-operator-chart --set deployKey=<deploy-key-goes-here> --namespace pl --create-namespace --set patches.vizier-pem='\{\"spec\"\: \{\"template\"\: \{\"spec\"\: \{ \"nodeSelector\"\: \{\"pixie\"\: \"allowed\" \}\}\}\}\}'
+```
+
 ## Providing a custom cluster name
 
 When deploying Pixie, you have the option of providing a custom cluster name. If you do not provide a cluster name, the name will be taken from the current kubeconfig.