Adds basic docs for prepared query templates.

website/source/docs/agent/dns.html.markdown

@@ -187,7 +187,10 @@ The `query or name` is the ID or given name of an existing
 [Prepared Query](/docs/agent/http/query.html). These behave like standard service
 queries but provide a much richer set of features, such as filtering by multiple
 tags and automatically failing over to look for services in remote datacenters if
-no healthy nodes are available in the local datacenter.
+no healthy nodes are available in the local datacenter. Consul 0.6.4 and later also
+added support for [prepared query templates](/docs/agent/http/query.html#templates)
+which can match names using a prefix match, allowing one template to apply to
+potentially many services.
 
 To allow for simple load balancing, the set of nodes returned is randomized each time.
 Both A and SRV records are supported. SRV records provide the port that a service is

website/source/docs/agent/http/query.html.markdown

@@ -17,6 +17,15 @@ service. This is particularly useful in combination with Consul's
 [DNS Interface](/docs/agent/dns.html) as it allows for much richer queries than
 would be possible given the limited entry points exposed by DNS.
 
+Consul 0.6.4 and later also supports prepared query templates. Templates are
+defined in a similar way to regular prepared queries but instead of applying to
+just a single query name, they can respond to names starting with a configured
+prefix. The service name being queried is computed using the matched prefix
+and/or a regular expression. This provides a powerful tool that lets you apply
+the features of prepared queries to a range (or potentially all) services with a
+small number of templates. Details about prepared query templates are covered
+[below](#templates).
+
 The following endpoints are supported:
 
 * [`/v1/query`](#general): Creates a new prepared query or lists
@@ -51,8 +60,8 @@ provided using the "?dc=" query parameter.
 If ACLs are enabled, the client will need to supply an ACL Token with `query`
 write privileges for the `Name` of the query being created.
 
-The create operation expects a JSON request body that defines the prepared query,
-like this example:
+The create operation expects a JSON request body that defines the prepared
+query, like this example:
 
 ```javascript
 {
@@ -157,6 +166,92 @@ a JSON body:
 }
 ```
 
+<a name="templates"><b>Prepared Query Templates</b></a>
+Consul 0.6.4 and later also support prepared query templates. These are created similar
+to static templates, except with some additional fields and features. Here's an example:
+
+```javascript
+{
+  "Name": "geo-db",
+  "Template" {
+    "Type": "name_prefix_match",
+    "Regexp": "^geo-db-(.*?)-([^\-]+?)$"
+  },
+  "Service": {
+    "Service": "mysql-${regexp.match(1)}",
+    "Failover": {
+      "NearestN": 3,
+      "Datacenters": ["dc1", "dc2"]
+    },
+    "OnlyPassing": true,
+    "Tags": ["${regexp.match(2)}"]
+  }
+}
+```
+
+The new `Template` structure configures a prepared query as a template instead of a
+static query. It has two fields:
+
+`Type` is the query type, which must be "name_prefix_match". This means that the
+template will apply to any query lookup with a name whose prefix matches the `Name`
+field of the template. In this example, any query for "geo-db" will match this
+query. Query templates are resolved using a longest prefix match, so it's possible
+to have high-level templates that are overridden for specific services. Static
+queries are always resolved first, so they can also override templates.
+
+`Regexp` is an optional regular expression which is used to extract fields from the
+entire name, once this template is selected. In this example, the regular expression
+takes the first item after the "-" as the database name and everything else after as
+a tag. See the [RE2](https://github.com/google/re2/wiki/Syntax) reference for syntax
+of this regular expression.
+
+All other fields of the query have the same meanings as for a static query, except
+that several interpolation variables are available to dynamically populate the query
+before it is executed. All of the string fields inside the `Service` structure are
+interpolated, with the following variables available:
+
+`${name.full}` has the entire name that was queried. For example, a lookup for
+"geo-db-customer-master.consul" in the example above would set this variable to
+"geo-db-customer-master".
+
+`${name.prefix}` has the prefix that matched. This would always be "geo-db" for
+the example above.
+
+`${name.suffix}` has the suffix after the prefix. For example, a lookup for
+"geo-db-customer-master.consul" in the example above would set this variable to
+"-customer-master".
+
+`${match(N)}` returns the regular expression match at the given index N. The
+0 index will have the entire match, and >0 will have the results of each match
+group. For example, a lookup for "geo-db-customer-master.consul" in the example
+above with a `Regexp` field set to `^geo-db-(.*?)-([^\-]+?)$` would return
+"geo-db-customer-master" for `${match(0)}`, "customer" for `${match(1)}`, and
+"master" for `${match(2)}`. If the regular expression doesn't match, or an invalid
+index is given, then `${match(N)}` will return an empty string.
+
+Using templates it's possible to apply prepared query behaviors to many services
+with a single template. Here's an example template that matches any query and
+applies a failover policy to it:
+
+```javascript
+{
+  "Name": "",
+  "Template" {
+    "Type": "name_prefix_match",
+  },
+  "Service": {
+    "Service": "${name.full}",
+    "Failover": {
+      "NearestN": 3,
+    }
+  }
+}
+```
+
+This will match any lookup for `*.query.consul` and will attempt to find the
+service locally, and otherwise attempt to find that service in the next three
+closest datacenters.
+
 #### GET Method
 
 When using the GET method, Consul will provide a listing of all prepared queries.
@@ -253,7 +348,8 @@ If the API call succeeds, a 200 status code is returned.
 
 The query execute endpoint supports only the `GET` method and is used to
 execute a prepared query. The \<query or name\> argument is the ID or name
-of an existing prepared query.
+of an existing prepared query, or a name that matches a prefix name for a
+[prepared query template](#templates).
 
 By default, the datacenter of the agent is queried; however, the `dc` can be
 provided using the "?dc=" query parameter. This endpoint does not support