Add support for dynamically generating the replica set configuration for mongo.

playbooks/roles/mongo/defaults/main.yml

 mongo_logappend: true
 mongo_version: 2.4.7
 mongo_bind_ip: 127.0.0.1
+mongo_port: "27017"
 mongo_extra_conf: ''
 mongo_key_file: '/etc/mongodb_key'
 mongo_repl_set: rs0
-mongo_cluster_members:
+mongo_cluster_members: []
 
 mongo_data_dir: "{{ COMMON_DATA_DIR }}/mongo"
 mongo_log_dir: "{{ COMMON_LOG_DIR }}/mongo"
@@ -19,3 +20,8 @@ MONGO_USERS:
 
 mongo_logpath: "{{ mongo_log_dir }}/mongodb.log"
 mongo_dbpath: "{{ mongo_data_dir }}/mongodb"
+
+# If the system is running out of an Amazon Web Services
+# cloudformation stack, this group name can used to pull out
+# the name of the stack the mongo server resides in.
+mongo_aws_stack_name: "tag_aws_cloudformation_stack-name_"

playbooks/roles/mongo/templates/mongodb.conf.j2

@@ -9,8 +9,14 @@ logpath={{ mongo_logpath }}
 
 logappend={{ mongo_logappend }}
 
+{# Bind to all ips(default) if in clustered mode, 
+   otherwise only to the specified local ip.
+#}
+{% if mongo_clustered is not defined %}
 bind_ip = {{ mongo_bind_ip }}
-#port = 27017
+{% endif %}
+
+port = {{ mongo_port }}
 
 # Enable journaling, http://www.mongodb.org/display/DOCS/Journaling
 journal=true

playbooks/roles/mongo/templates/repset_init.j2

+{# Generate a list of hosts if no cluster members are give. Otherwise use the
+   hosts provided in the variable.
+#}
+{%- if mongo_cluster_members|length == 0 -%}
+  {%- set hosts = [] -%}
+  {%- set all_mongo_hosts = [] -%}
+  {%- do all_mongo_hosts.extend(groups.tag_role_mongo) -%}
+  {%- do all_mongo_hosts.extend(groups.tag_group_mongo) -%}
+  {%- for name in  group_names -%}
+    {%- if name.startswith(mongo_aws_stack_name) -%}
+      {%- for host in all_mongo_hosts -%}
+        {%- if host in groups[name] -%}
+          {% do hosts.append("ip-" + host.replace('.','-') + ":" + mongo_port) %}
+        {%- endif -%}
+      {%- endfor -%}
+    {%- endif -%}
+  {%- endfor -%}
+{%- else -%}
+  {%- set hosts = mongo_cluster_members -%}
+{%- endif -%}
+
 config = {_id: '{{ mongo_repl_set }}', members: [
-	   {% for host in mongo_cluster_members %}
+	   {%- for host in hosts -%}
 	   {_id: {{ loop.index }}, host: '{{ host }}'}{% if not loop.last %},{% endif %}
-	   {% endfor %}
+	   {%- endfor -%}
            ]};
 rs.initiate(config)