Move imagepullpolicy into k8s deployment docs

**What**
- Move the content on the image pull policy into the k8s deployment doc
- Remove the section numbers because they were out of order and manual
numbering is fragile
- Change the sectioning so that image pull secrets and image pull policy
belong to a new "Customizing the install" section
- Move the Use the UI so that it is nested under the "Deploy a function"

Signed-off-by: Lucas Roesler <roesler.lucas@gmail.com>

Author: LucasRoesler

docs/deployment/kubernetes.md

@@ -6,7 +6,7 @@ This guide is for deployment to a vanilla Kubernetes 1.8 or 1.9 cluster running
 
 OpenFaaS is Kubernetes-native and uses *Deployments*, *Services* and *Secrets*. For more detail check out the ["faas-netes" repository](https://github.com/openfaas/faas-netes).
 
-### 1.0 Build a cluster
+### Build a cluster
 
 You can start evaluating FaaS and building functions on your laptop or on a VM (cloud or on-prem).
 
@@ -27,11 +27,11 @@ We have a special guide for minikube here:
       --user="$(gcloud config get-value core/account)"
     ```
 
-### 1.1 Pick helm or YAML files for deployment
+### Pick helm or YAML files for deployment
 
 If you'd like to use helm follow the instructions in 2.0a and then come back here, otherwise follow 2.0b to use plain `kubectl`.
 
-### 2.0a Deploy with Helm
+### Deploy with Helm
 
 A Helm chart is provided in the `faas-netes` repository. Follow the link below then come back to this guide.
 
@@ -41,7 +41,7 @@ To enable SSL while using Helm, try one of the following references:
 
 - [Using nginx-ingress and cert-manager](/reference/ssl/kubernetes-with-cert-manager.md)
 
-### 2.0b Deploy OpenFaaS
+### Deploy OpenFaaS
 
 This step assumes you are running `kubectl` on a master host.
 
@@ -74,7 +74,7 @@ This step assumes you are running `kubectl` on a master host.
     !!! note
         For deploying on a cloud that supports Kubernetes *LoadBalancers* you may also want to apply the configuration in: `cloud/lb.yml`.
 
-### 3.0 Use OpenFaaS
+### Use OpenFaaS
 
 After deploying OpenFaaS you can start using one of the guides or blog posts to create Serverless functions or test [community functions](https://github.com/openfaas/faas/blob/master/community.md).
 
@@ -164,7 +164,7 @@ c6ee9e33cf5c6715a1d148fd73f7318884b41adcb916021e2bc0e800a5c5dd97f5142178f6ae88c8
 
 [Your first serverless Python function with OpenFaaS](https://blog.alexellis.io/first-faas-python-function/)
 
-## Use the UI
+### Use the UI
 
 The UI is exposed on NodePort 31112.
 
@@ -188,7 +188,8 @@ $ echo -n "" | faas-cli invoke --gateway http://kubernetes-ip:31112 nodeinfo
 $ echo -n "verbose" | faas-cli invoke --gateway http://kubernetes-ip:31112 nodeinfo
 ```
 
-### 4.0 Use a private registry with Kubernetes
+## Customizing the install
+### Use a private registry with Kubernetes
 
 If you are using a hosted private Docker registry ([Docker Hub](https://hub.docker.com/), or other),
 in order to check how to configure it, please visit the Kubernetes [documentation](https://kubernetes.io/docs/concepts/containers/images/#using-a-private-registry).
@@ -302,12 +303,48 @@ imagePullSecrets:
 Save your changes.
 OpenFaaS will now deploy functions with images in private repositories without having to specify the secret in the deployment manifests.
 
-## 3.1 Start the hands-on labs
+### Setting the ImagePullPolicy with OpenFaaS
+
+Kubernetes allows you to control the conditions for when Docker images are pulled onto a node via the [imagePullPolicy](https://kubernetes.io/docs/concepts/containers/images/#updating-images) config. Your options are
+
+- `Always` : Kuberenetes will pull the Docker image from the registry every time
+- `IfNotPresent` : Kuberentes will only pull the image if it does not exist in the local registry cache
+- `Never` : Kuberenetes will never try to pull the image, you must manually ensure that the image already exists in the local cache
+
+By default, deployed functions will use an `imagePullPolicy` of `Always`, which ensures functions using static image tags (e.g. "latest" tags) are refreshed during an update. This behavior is configurable in `faas-netes` via the `image_pull_policy` environment variable. When installing via helm you can easily set this value during install using
+
+```
+helm upgrade openfaas openfaas/openfaas --install --set "faasnetesd.imagePullPolicy=IfNotPresent"
+```
+
+If installing via a custom yaml manifest, ensure that your `faas-netes` contain spec includes
+
+```
+env:
+  - name: image_pull_policy
+    value: "IfNotPresent"
+```
+
+[See here](/deployment/kubernetes/) for more details on deploying OpenFaaS in Kubernetes.
+
+#### Which imagePullPolicy should you use
+
+As mentioned above, the default value is `Always`. Every time a function is deployed or is scaled up, Kubernetes will pull a potentially updated copy of the image from the registry. If you are using static image tags like `latest`, this is necessary.
+
+When set to `IfNotPresent`, function deployments may not be updated when using static image tags like `latest`. `IfNotPresent` is particularly useful when developing locally with minikube. In this case, you can set your local environment to use [minikube's docker](https://github.com/kubernetes/minikube/blob/master/docs/reusing_the_docker_daemon.md) so `faas-cli build` builds directly into minikube's image store. `faas-cli push` is unnecessary in this workflow - use faas-cli build then faas-cli deploy.
+
+When set to `Never`, only local (or pulled) images will work. This is useful if you want to tightly control which images are available and run in your Kubernetes cluster.
+
+
+
+
+
+
+## Start the hands-on labs
 
 Learn how to build serverless functions with OpenFaaS and Python in our half-day workshop. You can follow along online at your own pace.
 
 * [OpenFaaS workshop](/tutorials/workshop/)
-
 ## Troubleshooting
 
 If you are running into any issues please check out the troubleshooting guide and search the documentation / past issues before raising an issue.

docs/reference/image-pull-policy.md

@@ -133,7 +133,6 @@ nav:
     - Triggers: ./reference/triggers.md
     - Workloads: ./reference/workloads.md
     - YAML: ./reference/yaml.md
-    - ImagePullPolicy: ./reference/image-pull-policy.md
   - Design & Architecture:
       - Gateway: ./architecture/gateway.md
       - Watchdog: ./architecture/watchdog.md