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Address comments from foxish, enisoc, and erictune

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Janet Kuo 2016-11-30 15:29:06 -08:00 committed by Devin Donnelly
parent 60855c25d9
commit eef081913b
1 changed files with 35 additions and 19 deletions
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54
docs/tasks/manage-stateful-set/scale-stateful-set.md
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@ -11,50 +11,52 @@ assignees:
---
{% capture overview %}
This page shows how to scale a Stateful Set.
This page shows how to scale a StatefulSet.
{% 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.
* StatefulSets are only available in Kubernetes version 1.5 or later.
* **Not all stateful applications scale nicely.** You need to understand your StatefulSets well before continuing. If you're unsure, remember that it might not be safe to scale your StatefulSets.
* You should perform scaling only when you're sure that your stateful application
cluster is completely healthy.
{% endcapture %}
{% capture steps %}
### Use `kubectl` to scale Stateful Sets
### Use `kubectl` to scale StatefulSets
#### `kubectl scale` (>= 1.4 release)
Make sure you have `kubectl` upgraded to Kubernetes version 1.5 or later before
continuing. If you're unsure, run `kubectl version` and check `Client Version`
for which kubectl you're using.
First, find the Stateful Set you want to scale. Remember, you need to first understand if you can scale it or not.
#### `kubectl scale`
First, find the StatefulSet 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:
Change the number of replicas of your StatefulSet:
```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`
#### Alternative: `kubectl apply` / `kubectl edit` / `kubectl patch` (>= 1.3 release)
Alternatively, you can do [in-place updates](/docs/user-guide/managing-deployments/#in-place-updates-of-resources) on your StatefulSets.
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`:
If your StatefulSet was initially created with `kubectl apply` or `kubectl create --save-config`,
update `.spec.replicas` of the StatefulSet 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`:
Otherwise, edit that field with `kubectl edit`:
```shell
kubectl edit statefulsets <stateful-set-name>
@ -70,14 +72,28 @@ kubectl patch statefulsets <stateful-set-name> -p '{"spec":{"replicas":<new-repl
#### 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).
You cannot scale down a StatefulSet when any of the stateful Pods it manages is unhealthy. Scaling down only takes place
after those stateful Pods become running and ready.
With a StatefulSet of size > 1, if there is an unhealthy Pod, there is no way
for Kubernetes to know (yet) if it is due to a permanent fault or a transient
one (upgrade/maintenance/node reboot). If it were a permanent fault, scaling
without paying heed to it may lead to a state where the StatefulSet membership
drops below a certain minimum number of "replicas" that are needed to function
correctly, leading to unavailability (or worse).
If it were a transient one and the Pod were coming back up shortly, you won't
want that to interleave with your scale-up/scale-down operation. Some distributed
databases have issues when nodes join and leave at the same time. It is better
to reason about scaling operations at the application level in these cases, and
perform scaling only when you're sure that your stateful application cluster is
completely healthy.
{% endcapture %}
{% capture whatsnext %}
*TODO: link to other docs about Stateful Set?*
*TODO: link to other docs about StatefulSet?*
{% endcapture %}
{% include templates/task.md %}