add documentation for coherence requirements

Author: markxnelson

docs-source/content/faq/coherence-requirements.md

@@ -0,0 +1,97 @@
+---
+title: "Coherence Requirements"
+date: 2019-08-12T12:41:38-04:00
+draft: false
+---
+
+If you are running Coherence on Kubernetes, either inside a WebLogic domain
+or standalone, then there are some additional requirements to make sure
+that Coherence can form clusters. 
+
+Note that some Fusion Middleware products, like SOA Suite, use Coherence
+and so these requirements apply to them.
+
+#### Unicast and Well Known Address 
+When the first Coherence process starts, it will form a cluster.  The next
+Coherence process to start (i.e. in a different pod) will use UDP to try
+to contact the master.  Most Kubernetes overlay network providers do not
+support multicast, so you should configure Coherence to use unicast and 
+provide a "well known address" so that members can find the master. 
+This is normally done by using the cluster address, i.e. the address of
+the Kubernetes service that is pointing to all cluster members.
+
+{{% notice note %}}
+If you create your domain using the samples provided in this project, the
+cluster will be able to form, you do not need to manually specify WKA.
+However, the information is included below for completeness.
+{{% /notice %}}
+
+For example, suppose you have a domain called `domain1` and in that domain
+you have a cluster called `cluster1` and Coherence is running in that
+cluster.  You would therefore use the cluster service that is created by
+the operator as the well known address.  This service, in this example, 
+would be called `domain1-cluster-cluster1` and follows the pattern:
+
+```
+domainUID  "-cluster-"  cluster name
+```
+
+Where `-cluster-` is a string literal. 
+
+The Coherence well known addresses are provided in a variable named
+`coherence.wka` as shown in the example below:
+
+```
+-Dcoherence.wka=domain1-cluster-cluster1
+```
+
+#### Operating system library requirements
+
+In order for coherence clusters to form correctly, the `conntrack` library
+must be installed.  Most Kubernetes distributions will do this for you.
+If you have issues with clusters not forming, you should check that 
+`conntrack` is installed using this command (or equivalent):
+
+```
+$ rpm -qa | grep conntrack
+libnetfilter_conntrack-1.0.6-1.el7_3.x86_64
+conntrack-tools-1.4.4-4.el7.x86_64
+```
+
+You should see output similar to that shown above.  If you do not, then you
+should install `conntrack` using your operating system tools.
+
+#### Firewall (iptables) requirements
+
+Some Kubernetes distributions create `iptables` rules that block some
+types of traffic that Coherence requires to form clusters.  If you are
+not able to form clusters, you can check for this issue using the
+following command:
+
+```
+# iptables -t nat -v  -L POST_public_allow -n
+Chain POST_public_allow (1 references)
+pkts bytes target     prot opt in     out     source               destination
+164K   11M MASQUERADE  all  --  *      !lo     0.0.0.0/0            0.0.0.0/0
+   0     0 MASQUERADE  all  --  *      !lo     0.0.0.0/0            0.0.0.0/0
+```
+
+If you see output similar to the example above, i.e. if you see any entries 
+in this chain, then you need to remove them.  You can remove the entries
+using this command:
+
+```
+# iptables -t nat -v -D POST_public_allow 1
+```
+
+Note that you will need to run that command for each line. So in the example
+above, you would need to run it twice. 
+
+Once you are done, you can run the previous command again and verify that
+the output is now an empty list.
+
+After making this change, restart your domain(s) and the Coherence cluster
+should now form correctly. 
+
+
+

docs-source/content/userguide/managing-domains/fmw-infra/_index.md

@@ -15,6 +15,7 @@ pre = "<b> </b>"
 * [Create a Kubernetes secret with the RCU credentials](#create-a-kubernetes-secret-with-the-rcu-credentials)
 * [Creating an FMW Infrastructure domain](#creating-an-fmw-infrastructure-domain)
 * [Patching the FMW Infrastructure image](#patching-the-fmw-infrastructure-image)
+* [Additional considerations for Coherence](#additional-considerations-for-coherence)
 
 
 Starting with the 2.2.0 release, the operator supports FMW Infrastructure domains, that is,
@@ -431,3 +432,10 @@ for more information.
 
 An example of a non-ZDP compliant patch is one that includes a schema change
 that cannot be applied dynamically.
+
+#### Additional considerations for Coherence
+
+If you are running a domain which contains Coherence, please refer to
+[Coherence requirements]({{< relref "/faq/coherence-requirements.md" >}})
+for more information.
+