Merge pull request sorintlab#552 from sgotti/doc_two_nodes_setup

doc: add a two nodes example

Author: sgotti

README.md

@@ -41,8 +41,9 @@ For more details and requirements see [Stolon Architecture and Requirements](doc
 
 ## Quick start and examples
 
-* [simple cluster example](doc/simplecluster.md)
-* [kubernetes example](examples/kubernetes/README.md)
+* [Simple cluster example](doc/simplecluster.md)
+* [Kubernetes example](examples/kubernetes/README.md)
+* [Two (or more) nodes setup](doc/twonodes.md)
 
 ## Project Status
 

doc/README.md

@@ -15,15 +15,19 @@ We suggest that you first read the [Stolon Architecture and Requirements](archit
 * [Standby Cluster](standbycluster.md)
 
 ### Misc topics
-  * [Enabling pg_rewind](pg_rewind.md)
-  * [Enabling synchronous replication](syncrepl.md)
-  * [PostgreSQL SSL/TLS setup](ssl.md)
+
+* [Enabling pg_rewind](pg_rewind.md)
+* [Enabling synchronous replication](syncrepl.md)
+* [PostgreSQL SSL/TLS setup](ssl.md)
 
 ### Recipes
-  * [Manual switchover without transactions loss](manual_switchover.md)
+
+* [Manual switchover without transactions loss](manual_switchover.md)
 
 ### Examples
-  * [Simple test cluster](simplecluster.md)
-  * [Kubernetes](../examples/kubernetes/README.md)
+
+* [Simple test cluster](simplecluster.md)
+* [Kubernetes](../examples/kubernetes/README.md)
+* [Two (or more) nodes setup](twonodes.md)
 
 ### [FAQ](faq.md)

doc/twonodes.md

@@ -0,0 +1,29 @@
+# Two (or more) nodes setup example
+
+If you're going to run stolon on an IaaS or any kind of two nodes (baremetal, VM) this document provides some example configurations. These examples provide a two nodes setup that can be extended to a number greater than two nodes.
+
+The related store should live outside the instances hosting the stolon cluster for multiple reasons:
+
+* Stores like etcd/consul uses the raft consensus protocol that requires at least 3 nodes to provides high availability (it can survive to the death of (N/2)-1 members)
+* Disk I/O of postgres must not impact the etcd/consul I/O
+* You can run multiple stolon clusters using the same store
+
+# Two nodes with load balancer
+
+![Two nodes with a load balancer](twonodes_lb_small.png)
+
+Every nodes will run one keeper, one sentinel and one proxy.
+
+The load balancer will balance between the stolon proxies.
+
+Clients will connect to the load balancer VIP.
+
+# Two nodes with keepalived
+
+![Two nodes with keepalived](twonodes_keepalived_small.png)
+
+Every nodes will run one keeper, one sentinel and one proxy.
+
+Every nodes also runs a [keepalived](http://www.keepalived.org/) instance that will mantain a VIP assigned to one of the nodes. If one of the nodes dies/become partitioned keepealived will switch the VIP to the other node.
+
+Clients will connect to the VIP managed by keepalived.