Adds a draft of the snapshot agent docs.

website/source/docs/commands/snapshot.html.markdown

@@ -29,6 +29,7 @@ Usage: consul snapshot <subcommand> [options] [args]
 
 Subcommands:
 
+    agent      Periodically saves snapshots of Consul server state
     inspect    Displays information about a Consul snapshot file
     restore    Restores snapshot of Consul server state
     save       Saves snapshot of Consul server state
@@ -37,6 +38,7 @@ Subcommands:
 For more information, examples, and usage about a subcommand, click on the name
 of the subcommand in the sidebar or one of the links below:
 
+- [agent] (/docs/commands/snapshot/agent.html) (Consul Enterprise only)
 - [inspect] (/docs/commands/snapshot/inspect.html)
 - [restore](/docs/commands/snapshot/restore.html)
 - [save](/docs/commands/snapshot/save.html)
@@ -68,5 +70,11 @@ Term         2
 Version      1
 ```
 
+To run a daemon process that periodically saves snapshots (Consul Enterprise only):
+
+```
+$ consul snapshot agent
+```
+
 For more examples, ask for subcommand help or view the subcommand documentation
 by clicking on one of the links in the sidebar.

website/source/docs/commands/snapshot/agent.html.markdown.erb

@@ -0,0 +1,156 @@
+---
+layout: "docs"
+page_title: "Commands: Snapshot Agent"
+sidebar_current: "docs-commands-snapshot-agent"
+---
+
+# Consul Snapshot Agent
+
+Command: `consul snapshot agent`
+
+~> The [`agent`](/docs/commands/snapshot/agent.html) subcommand described here is
+   available only in [Consul Enterprise](https://www.hashicorp.com/consul.html)
+   version 0.7.1 and later. All other [snapshot subcommands](/docs/commands/snapshot.html)
+   are available in the open source version of Consul.
+
+The `snapshot agent` subcommand starts a process that takes snapshots of the
+state of the Consul servers and saves them locally, or pushes them to an
+optional remote storage service. This subcommand is only available in Consul
+Enterprise 0.7.1 and later.
+
+The agent can be run as a long-running daemon process or in a one-shot mode
+from a batch job, based on the [`-interval`](#interval) argument. Snapshotting
+a remote datacenter is only available in one-shot mode.
+
+As a long-running daemon, the agent will perform a leader election so multiple
+processes can be run in a highly available fashion with automatic failover. The
+agent will also register itself with Consul as a service, along with health
+checks that show the agent is alive ("Consul Snapshot Agent Alive") and able to
+take snapshots ("Consul Snapshot Agent Saving Snapshots"). The latter check is
+only added on agents who have become a leader, so it's possible for operators to
+tell which instances are alive and on standby and which instance has become
+leader and starting saving snapshots.
+
+As snapshots are saved, they will be reported in the log produced by the agent:
+
+```
+2016/11/16 21:21:13 [INFO] Snapshot agent running
+2016/11/16 21:21:13 [INFO] Waiting to obtain leadership...
+2016/11/16 21:21:13 [INFO] Obtained leadership
+2016/11/16 21:21:13 [INFO] Saved snapshot 1479360073448728784
+```
+
+The number shown with the saved snapshot is its ID, which is based on a UNIX
+timestamp with nanosecond resolution, so collisions are unlikely and IDs are
+monotonically increasing with time. This makes it easy to locate the latest
+snapshot, even if the log data isn't available. The snapshot ID always appears
+in the file name when using local storage, or in the object key when using
+remote storage.
+
+Snapshots can be restored using the
+[`consul snapshot restore`](/docs/commands/snapshot/restore.html) command, or
+the [HTTP API](/docs/agent/http/snapshot.html).
+
+If ACLs are enabled, a management token must be supplied in order to perform
+snapshot operations.
+
+## Usage
+
+Usage: `consul snapshot agent [options]`
+
+#### API Options
+
+<%= partial "docs/commands/http_api_options" %>
+
+#### Snapshot Options
+
+* <a name="interval">`-interval`</a> - Interval at which to perform snapshots
+  as a time with a unit suffix, which can be "s", "m", "h" for seconds, minutes,
+  or hours. If 0 is provided, the agent will take a single snapshot and then exit,
+  which is useful for running snapshots via batch jobs. Defaults to "1h"
+
+* `-lock-key` - A prefix in Consul's key-value store used to coordinate between
+  different instances of the snapshot agent order to only have one active instance
+  at a time. For highly available operation of the snapshot agent, simply run
+  multiple instances. All instances must be configured with the same lock key in
+  order to properly coordinate. Defaults to "consul-snapshot/lock".
+
+* `-max-failures` - Number of snapshot failures after which the snapshot agent
+  will give up leadership. In a highly available operation with multiple snapshot
+  agents available, this gives another agent a chance to take over if an agent
+  is experiencing issues, such as running out of disk space for snapshots.
+  Defaults to 3.
+
+* `-retain` - Number of snapshots to retain. After each snapshot is taken, the
+  oldest snapshots will start to be deleted in order to retain at most this many
+  snapshots. If this is set to 0, the agent will not perform this and snapshots
+  will accumulate forever. Defaults to 30.
+
+
+#### Agent Options
+
+* `-deregister-after` - An interval, after which if the agent is unhealthy it will be
+  automatically deregistered from Consul service discovery. This is a time with a
+  unit suffix, which can be "s", "m", "h" for seconds, minutes, or hours. If 0 is
+  provided, this will be disabled. Defaults to "72h".
+
+* `-log-level` - Controls verbosity of snapshot agent logs. Valid options are
+  "TRACE", "DEBUG", "INFO", "WARN", "ERR". Defaults to "INFO".
+
+* `-service` - The service name to used when registering the agent with Consul.
+  Registering helps monitor running agents and the leader registers an additional
+  health check to monitor that snapshots are taking place. Defaults to
+  "consul-snapshot".
+
+* `-syslog` - This enables forwarding logs to syslog. Defaults to false.
+
+* `-syslog-facility` - Sets the facility to use for forwarding logs to syslog.
+  Defaults to "LOCAL0".
+
+#### Local Storage Options
+
+* `-snapshot-path` - Location to store snapshots locally. The default behavior
+  of the snapshot agent is to store snapshots locally in this directory. Defaults
+  to "." to use the current working directory. If an alternate storage option is
+  configured, then local storage will be disabled and this option will be ignored.
+
+#### Amazon S3 Storage Options
+
+* `-aws-access-key-id` and `-aws-secret-access-key` - These arguments supply
+  authentication information for connecting to AWS. These may also be supplied using
+  the following alternative methods:<br>
+  - `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` environment variables
+  - A credentials file (`~/.aws/credentials` or the file at the path specified by the
+    `AWS_SHARED_CREDENTIALS_FILE` environment variable)
+  - ECS task role metadata (container-specific)
+  - EC2 instance role metadata
+
+* `-aws-s3-bucket` - S3 bucket to use. Required for S3 storage, and setting this
+  disables local storage.
+
+* `-aws-s3-key-prefix` - Prefix to use for snapshot files in S3. Defaults to
+   "consul-snapshot".
+
+* `-aws-s3-region` - S3 region to use. Required for S3 storage.
+
+## Examples
+
+Running the agent with no arguments will run a long-running daemon process that will
+perform leader election for highly available operation, register itself with Consul
+service discovery with health checks, take snapshots every hour, retain the last 30
+snapshots, and save snapshots into the current working directory:
+
+```
+$ consul snapshot agent
+```
+
+To run a one-shot backup, set the backup interval to 0. This will run a single snapshot
+and delete any old snapshots based on the retain settings, but it will not perform any
+leader election or service registration:
+
+```
+$ consul snapshot agent -interval=0
+```
+
+Please see the [HTTP API](/docs/agent/http/snapshot.html) documentation for
+more details about snapshot internals.

website/source/layouts/docs.erb

@@ -152,6 +152,9 @@
 					<li<%= sidebar_current("docs-commands-snapshot") %>>
 					<a href="/docs/commands/snapshot.html">snapshot</a>
 					<ul class="subnav">
+						<li<%= sidebar_current("docs-commands-snapshot-agent") %>>
+							<a href="/docs/commands/snapshot/agent.html">agent</a>
+						</li>
 						<li<%= sidebar_current("docs-commands-snapshot-inspect") %>>
 							<a href="/docs/commands/snapshot/inspect.html">inspect</a>
 						</li>