Add guide for GKE checks (#162)

Signed-off-by: Jose Fuentes <[email protected]>

Author: j-fuentes

docs/guides/gke_local/guide.md

@@ -0,0 +1,105 @@
+# How to run Preflight with the GKE package
+
+This doc guides you on how to run preflight-agent locally to scan a GKE installation.
+
+As a result, you will get a new cluster in your Preflight account showing reports with the GKE package.
+
+It executes the agent locally because this guide is intented to be an interative demonstration, but the agent could be installed in-cluster as well. Take a look at the [GKE data-gatherer manual](../../datagatherers/gke.md) for further details on how to configure authentication in that scenario.
+
+## Requisites
+
+- A GKE cluster.
+- The `gcloud` CLI tool working locally on your computer.
+- `gcloud` is logged in to an account with permissions to read cluster and GKE state in the project where your cluster is running.
+- You have already run `gcloud container clusters get-credentials [cluster] ...` to configure your kubeconfig.
+
+## Get the preflight cli
+
+Go to [the releases page](https://github.com/jetstack/preflight/releases) and download the binary of the latest stable release for your platform (`v0.1.15` at the moment of writing this).
+
+![release](./img/release.png)
+
+For instance:
+
+```
+curl -L https://github.com/jetstack/preflight/releases/download/v0.1.15/preflight-linux-amd64 > preflight 
+chmod +x ./preflight
+```
+
+Then run this to make sure you downloaded the right thing:
+
+```
+./preflight version
+```
+
+## Access Preflight
+
+> At the moment, Preflight is in private beta. If you are interested, please [email us](mailto:[email protected]?subject=Preflight%20Beta%20Access) and we will grant to access to the beta program.
+
+If you have an account, you will have an access token.
+
+Enter [preflight.jetstack.io/login](https://preflight.jetstack.io/login) and access with your token.
+
+You will be presented with the list of cluster in your organization.
+
+## Add a new cluster and start agent
+
+Click in "Add Cluster".
+
+Choose a name for your cluster (e.g. `my-gke-cluster`) and click the accept button.
+
+Then you will be presented with instructions to install the agent in a cluster.
+
+Since you are going to run the agent locally instead of installing it in a cluster, you must copy the agent token and craft a config file manually.
+
+You can extract the agent token from the installation command, as shown in the picture.
+
+![token](./img/select_token.png)
+
+Then you can use this snipped as template for your configuration file and replace the agent token where it corresponds.
+
+Also, change `cluster.project`, `cluster.location`, `cluster.name` accordingly so they point to your GKE cluster (`gcloud container clusters list` if you don't remember those values.).
+
+If you don't specify `credentials`, it will try to use _Gcloud Application Default Credentials_. You can run `gcloud auth application-default login` to make sure your _Application Default Credentials_ are configured.
+
+```yaml
+# config.yaml
+
+schedule: "* * * *"
+token: "<add your agent token here>"
+endpoint:
+  protocol: https
+  host: "preflight.jetstack.io"
+  path: "/api/v1/datareadings"
+data-gatherers:
+- kind: "gke"
+  name: "gke"
+  config:
+    cluster:
+      project: my-gcp-project
+      location: us-central1-a
+      name: my-gke-cluster
+      # Path to a file containing the credentials. If empty, it will try to use
+      # the SDK defaults
+      # credentials: /tmp/credentials.json
+```
+
+Save the file as `config.yaml`.
+
+Now you can run the Preflight agent:
+
+```
+./preflight agent -c ./config.yaml
+```
+
+You should see in the log that it is sending data to the server periodically.
+
+If you go back to the add cluster wizard and click "The agent it ready"
+
+![ready](./img/ready.png)
+
+## See reports
+
+If you go to the clusters view, you will see the new cluster is there:
+
+![cluster](./img/cluster.png)