Add task: scaling stateful sets

_data/tasks.yml

@@ -37,3 +37,5 @@ toc:
   section:
   - title: Upgrading from PetSets to StatefulSets
     path: /docs/tasks/manage-stateful-set/upgrade-pet-set-to-stateful-set/
+  - title: Scaling a Stateful Set
+    path: /docs/tasks/manage-stateful-set/scale-stateful-set/

docs/tasks/index.md

@@ -31,6 +31,7 @@ single thing, typically by giving a short sequence of steps.
 #### Managing Stateful Applications
 
 * [Upgrading from PetSets to StatefulSets](/docs/tasks/manage-stateful-set/upgrade-pet-set-to-stateful-set/)
+* [Scaling a Stateful Set](/docs/tasks/manage-stateful-set/scale-stateful-set/)
 
 ### What's next
 

docs/tasks/manage-stateful-set/scale-stateful-set.md

@@ -0,0 +1,83 @@
+---
+assignees:
+- bprashanth
+- enisoc
+- erictune
+- foxish
+- janetkuo
+- kow3ns
+- smarterclayton
+
+---
+
+{% capture overview %}
+This page shows how to scale a Stateful Set.
+{% endcapture %}
+
+{% capture prerequisites %}
+
+* Stateful Sets are only available in Kubernetes release >= 1.5. 
+* Stateful Sets are previously known as Pet Sets in Kubernetes release 1.3-1.4. You can either upgrade your Pet Sets to Stateful Sets, 
+or just change all `statefulset` references to `petset`. *TODO: link to upgrade from Pet Sets to Stateful Sets.*
+* **Not all stateful applications scale nicely.** You need to understand your Stateful Sets well before continue. If you're unsure, remember that it may not be safe to scale your Stateful Sets. 
+
+{% endcapture %}
+
+{% capture steps %}
+
+### Use `kubectl` to scale Stateful Sets
+
+#### `kubectl scale` (>= 1.4 release)
+
+First, find the Stateful Set you want to scale. Remember, you need to first understand if you can scale it or not. 
+
+```shell
+kubectl get statefulsets <stateful-set-name>
+```
+
+If you wish to change the number of replicas of your Stateful Set, just use this command:
+
+```shell
+kubectl scale statefulsets <stateful-set-name> --replicas=<new-replicas>
+```
+
+Note that `kubectl scale` only works on Stateful Set with Kubernetes release >= 1.4. 
+
+#### Alternative: `kubectl apply` / `kubectl edit` / `kubectl patch` (>= 1.3 release) 
+
+Alternatively, you may do [in-place updates](/docs/user-guide/managing-deployments/#in-place-updates-of-resources) on your Stateful Sets. 
+
+If your Stateful Set was initially created with `kubectl apply` or `kubectl create --save-config`, 
+you may update `.spec.replicas` of the Stateful Set manifests, and then do a `kubectl apply`:
+
+```shell 
+kubectl apply -f <stateful-set-file-updated>
+```
+
+Otherwise, you can just edit that field with `kubectl edit`:
+
+```shell 
+kubectl edit statefulsets <stateful-set-name>
+```
+
+Or use `kubectl patch`:
+
+```shell 
+kubectl patch statefulsets <stateful-set-name> -p '{"spec":{"replicas":<new-replicas>}}'
+```
+
+### Troubleshooting
+
+#### Scaling down doesn't not work right
+
+You cannot scale down a Stateful Set when some of the stateful pods it manages are unhealthy. Scaling down only takes place
+after those stateful pods become running and ready. See discussions [here](https://github.com/kubernetes/kubernetes/issues/36333). 
+
+
+{% endcapture %}
+
+{% capture whatsnext %}
+*TODO: link to other docs about Stateful Set?*
+{% endcapture %}
+
+{% include templates/task.md %}