Definitions

Cloud workflows consist of a sequence of statements. Each statement consists of one or more expressions. The first expression is the define...end block:

define main(@servers, $wait) return @instances, $duration do
 ​ $now = now()
  @instances = @servers.launch()
  if $wait
   ​ sleep_until(all?(@instances.state, "operational")) timeout: 15mn
  end
  $duration = $now - now()
end

A cloud workflow may contain any number of definitions. The special definition called main is the entry point to the process.

Definitions are scoped by the file that contain them: two definitions in the same file cannot have the same name.

Inputs and Outputs

As shown in the snippet above a cloud workflow may specify arguments and return values. There can be zero or more arguments and zero or more return values. Arguments and return values can either be references (@server and @instance) or variables ($wait and $duration), the difference being that references contain resource collections while variables may contain a number, a string, a boolean, a time value, the special null value, an array or a hash (references are described in Cloud Workflow Resources and variables are described in Cloud Workflow Variables).

A cloud workflow may execute children definitions using the call keyword:

define launch_servers(@servers, $wait) return @instances, $duration
  $now = now()
  @instances = @servers.launch()
  if $wait
    sleep_until(all?(@instances.state, "operational")) timeout: 15mn
  end
  $duration = $now - now()
end

define run_application do
 ​@servers = rs.tags.by_tag(resource_type: "servers", tags: ["my_site:role=app"])
  call launch_servers(@servers, true) retrieve @launched_instances, $duration
end

This run_application definition first initializes the @servers resources collection using a tag query then passes the collection of retrieved servers to the launch_servers definition above. The list of references and variables specified after the retrieve keyword matches the list after the return keyword of the definition. These references and variables are initialized with the return values of the definition (so in this example the reference @launched_instances of the caller is initialized with the value of the @instances reference returned by launch_servers). The names can match, but don't have to as shown in the example. 

Note: Using retrieve is optional and can be skipped if the caller does not need the return values.

@instances = @servers.launch() # Comments can appear at the end of a line
sleep_until(all?(@instances.state[], "operational"))

# is equivalent to:
@instances = @servers.launch();
sleep_until(all?(@instances.state[], "operational"));
 
# and to:
@instances = @servers.launch(); sleep_until(all?(@instances.state[], "operational"))

sub do
  @servers = rs.servers.get(filter: ["name==my_server"])
  @servers.launch()
end
sub do
  @servers = rs.servers.get(filter: ["name==my_other_server"])
  @servers.launch()
end