+ Host filtering
+You may encounter situations where you only want to deploy to a subset of +the servers defined in your configuration. For example, a single server or +set of servers may be misbehaving, and you want to re-deploy to just these +servers without deploying to every server.
+ +You can use the host filter to restrict Capistrano tasks to only servers +that match a given set of hostnames.
+ +If the filter matches no servers, no actions will be taken.
+ +If you specify a filter, it will match servers that have the listed hostnames, +and it will run all the roles for each server. In other words, it only affects +the servers the task runs on, not what tasks are run on a server.
+ +You can limit by role and by host; if you do this, the role filtering will
+apply first. For example, lets say you filtered by the role app, then by
+the hostnames server1 and server2. Capistrano would first filter the
+available servers to only those with the role app, then filter them
+to look for servers with the hostname server1 or server2. If only server2
+had the role app (server1 has some other role), then in this situation your
+task would only run on server2.
Specifying a host filter
+ +There are three ways to specify the host filter.
+ +Environment variable
+ +Capistrano will read the host filter from the environment variable HOSTS
+if it is set. You can set it inline:
HOSTS=server1,server2 cap production deploySpecify multiple hosts by separating them with a comma.
+ +In configuration
+ +You can set the host filter inside your deploy configuration. For example,
+you can set the following inside config/deploy.rb:
set :filter, :hosts => %w{server1 server2}Note that you specify the filter as an array rather than as a comma-separated +list of servers when using this method.
+ +On the command line
+ +In a similar way to using the environment variable, you can set the role
+filter by specifying it as a command line argument to cap:
cap --hosts=server1,server2 production deployLike the environment variable method, specify multiple servers by separating +them with a comma.
+ +