Document `TCP` check type

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

@@ -31,6 +31,20 @@ There are three different kinds of checks:
   It is possible to configure a custom HTTP check timeout value by specifying
   the `timeout` field in the check definition.
 
+* TCP + Interval - These checks make an TCP connection attempt every Interval
+  (e.g. every 30 seconds) to the specified IP/hostname and port. The status of
+  the service depends on whether the connection attempt is successful (ie - the
+  port is currently accepting connections). If the connection is accepted, the
+  status is `success`, otherwise the status is `critical`. In the case of a
+  hostname that resolves to both IPv4 and IPv6 addresses, an attempt will be
+  made to both addresses, and the first successful connection attempt will
+  result in a successful check. This type of check should be preferred over a
+  script that uses `netcat` or another external process to check a simple socket
+  operation. By default, TCP checks will be configured with a request timeout
+  equal to the check interval, with a max of 10 seconds. It is possible to
+  configure a custom TCP check timeout value by specifying the `timeout` field
+  in the check definition.
+
 * <a name="TTL"></a>Time to Live (TTL) - These checks retain their last known state for a given TTL.
   The state of the check must be updated periodically over the HTTP interface. If an
   external system fails to update the status within a given TTL, the check is
@@ -75,6 +89,20 @@ A HTTP check:
 }
 ```
 
+A TCP check:
+
+```javascript
+{
+  "check": {
+    "id": "ssh",
+    "name": "SSH TCP on port 22",
+    "tcp": "localhost:22",
+    "interval": "10s",
+    "timeout": "1s"
+  }
+}
+```
+
 A TTL check:
 
 ```javascript
@@ -102,7 +130,7 @@ Checks may also contain a `token` field to provide an ACL token. This token is
 used for any interaction with the catalog for the check, including
 [anti-entropy syncs](/docs/internals/anti-entropy.html) and deregistration.
 
-Both script and HTTP checks must include an `interval` field. This field is
+Script, TCP and HTTP checks must include an `interval` field. This field is
 parsed by Go's `time` package, and has the following
 [formatting specification](http://golang.org/pkg/time/#ParseDuration):
 > A duration string is a possibly signed sequence of decimal numbers, each with

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

@@ -224,8 +224,8 @@ The endpoint always returns 200.
 
 The register endpoint is used to add a new check to the local agent.
 There is more documentation on checks [here](/docs/agent/checks.html).
-Checks may be of script, HTTP, or TTL type. The agent is responsible for managing
-the status of the check and keeping the Catalog in sync.
+Checks may be of script, HTTP, TCP, or TTL type. The agent is responsible for
+managing the status of the check and keeping the Catalog in sync.
 
 The register endpoint expects a JSON request body to be PUT. The request
 body must look like:
@@ -237,13 +237,14 @@ body must look like:
   "Notes": "Ensure we don't oversubscribe memory",
   "Script": "/usr/local/bin/check_mem.py",
   "HTTP": "http://example.com",
+  "TCP": "example.com:22",
   "Interval": "10s",
   "TTL": "15s"
 }
 ```
 
-The `Name` field is mandatory, as is one of `Script`, `HTTP` or `TTL`.
-`Script` and `HTTP` also require that `Interval` be set.
+The `Name` field is mandatory, as is one of `Script`, `HTTP`, `TCP` or `TTL`.
+`Script`, `TCP` and `HTTP` also require that `Interval` be set.
 
 If an `ID` is not provided, it is set to `Name`. You cannot have duplicate
 `ID` entries per agent, so it may be necessary to provide an `ID`.
@@ -258,6 +259,14 @@ be a URL) every `Interval`. If the response is any `2xx` code, the check is `pas
 If the response is `429 Too Many Requests`, the check is `warning`. Otherwise, the check
 is `critical`.
 
+An `TCP` check will perform an TCP connection attempt against the value of `TCP`
+(expected to be an IP/hostname and port combination) every `Interval`.  If the
+connection attempt is successful, the check is `passing`.  If the connection
+attempt is unsuccessful, the check is `critical`.  In the case of a hostname
+that resolves to both IPv4 and IPv6 addresses, an attempt will be made to both
+addresses, and the first successful connection attempt will result in a
+successful check.
+
 If a `TTL` type is used, then the TTL update endpoint must be used periodically to update
 the state of the check.
 

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

@@ -62,13 +62,14 @@ the DNS interface as well. If a service is failing its health check or a
 node has any failing system-level check, the DNS interface will omit that
 node from any service query.
 
-The check must be of the script, HTTP, or TTL type. If it is a script type, `script`
-and `interval` must be provided. If it is a HTTP type, `http` and
-`interval` must be provided. If it is a TTL type, then only `ttl` must be
-provided. The check name is automatically generated as
-`service:<service-id>`. If there are multiple service checks registered, the
-ID will be generated as `service:<service-id>:<num>` where `<num>` is an
-incrementing number starting from `1`.
+The check must be of the script, HTTP, TCP or TTL type. If it is a script type,
+`script` and `interval` must be provided. If it is a HTTP type, `http` and
+`interval` must be provided. If it is a TCP type, `tcp` and `interval` must be
+provided. If it is a TTL type, then only `ttl` must be provided. The check name
+is automatically generated as `service:<service-id>`. If there are multiple
+service checks registered, the ID will be generated as
+`service:<service-id>:<num>` where `<num>` is an incrementing number starting
+from `1`.
 
 Note: there is more information about [checks here](/docs/agent/checks.html).