docs(managing-workflow): add Security Considerations

Author: Matthew Fisher

src/managing-workflow/security-considerations.md

@@ -1,3 +1,55 @@
 # Security Considerations
 
-TODO (bacongobbler): rewrite for v2
+!!! important
+	Workflow is not suitable for multi-tenant environments or hosting untrusted code.
+
+A major goal of Workflow is to be operationally secure and trusted by operations engineers in every
+deployed environment. There are, however, two notable security-related considerations to be aware
+of when deploying Workflow.
+
+# Application Runtime Segregation
+
+Users of Workflow often want to deploy their applications to separate environments. Typically,
+physical network isolation isn’t the goal, but rather segregation of application environments - if a
+region goes haywire, it shouldn’t affect applications that are running in a separate region.
+
+In Workflow, deployed applications can be segregated by using the `deis tags` command. This enables
+you to tag machines in your cluster with arbitrary metadata, then configure your applications to be
+scheduled to machines which match the metadata.
+
+For example, if some machines in your cluster are tagged with `region=us-west-1` and some
+with `region=us-east-1`, you can configure an application to be deployed to us-west-1
+by using `deis tags set region=us-west-1`. Workflow will pass this configuration
+along to Kubernetes, which will schedule your application in different regions.
+
+# Running Workflow on Public Clouds
+
+If you are running on a public cloud without security group features, you will have to set up
+security groups yourself through either `iptables` or a similar tool. The only ports on worker
+nodes that should be exposed to the public are:
+
+ - 22: (optional) for remote SSH
+ - 80: for the routers
+ - 443: (optional) routers w/ SSL enabled
+ - 2222: for the routers proxying TCP to the builder
+ - 9090: for the routers' health check
+
+# IP Whitelist
+
+Enforcing a cluster-wide IP whitelist may be advisable for routers governing ingress to a cluster
+that hosts applications intended for a limited audience-- e.g. applications for internal use within
+an organization. You can enforce cluster-wide IP whitelisting by enabling whitelists, then
+attaching an annotation to the router:
+
+$ kubectl --namespace=deis annotate replicationcontroller deis-router router.deis.io/nginx.enforceWhitelists=true
+$ kubectl --namespace=deis annotate replicationcontroller deis-router router.deis.io/nginx.defaultWhitelist="0.0.0.0/0"
+
+The format is the same for the controller whitelist but you need to specify the whitelist directly
+to the controller's service. For example:
+
+$ kubectl --namespace=deis annotate service deis-controller router.deis.io/whitelist="10.0.1.0/24:office_intranet,121.212.121.212:dev_jenkins"
+
+And the same applies to applications. For example, to apply a whitelist to an application named
+`example`:
+
+$ kubectl --namespace=example annotate service example-web router.deis.io/whitelist="10.0.1.0/24:office_intranet,121.212.121.212:dev_jenkins"