What are AScript built-in variables - Server Load Balancer

AScript is an easy-to-use programmable scripting feature that provides more complex forwarding rule configuration capabilities than the settings available in the Application Load Balancer (ALB) console. This topic describes AScript built-in variables and the corresponding NGINX variables.

Built-in variables

The following table describes the AScript built-in variables.

Built-in variable	Description	NGINX variable
$arg_{name}	The value of the `name` parameter in the `query string`. The `query string` represents request parameters in an HTTP request.	ngx.var.arg_{name} Note Hyphens (-) in the `{name}` field must be replaced by underscores (_). For example, `X-USER-ID` must be changed to `$arg_x_user_id`.
$http_{name}	The value of the `name` field in the request header.	ngx.var.http_{name} Note Hyphens (-) in the `{name}` field must be replaced by underscores (_). For example, `X-USER-ID` must be changed to `$http_x_user_id`.
$cookie_{name}	The value of the `name` field in the request cookie header.	ngx.var.cookie_{name} Note Hyphens (-) in the `{name}` field must be replaced by underscores (_). For example, `X-USER-ID` must be changed to `$cookie_x_user_id`.
$scheme	The protocol type.	ngx.var.scheme
$server_protocol	The version of the protocol.	ngx.var.server_protocol
$host	The original host.	ngx.var.host
$uri	The original URI.	ngx.var.raw_uri
$args	`$args` represents all request parameters in an HTTP request, excluding question marks (`?`). For example, the URI of the request is `http://www.a.com/1k.file?k1=v1&k2=v2`. `$arg_k1` returns the value of the k1 parameter: `v1`. `$args` is used to return the entire query string: `k1=v1&k2=v2`. Question marks (`?`) are excluded.	ngx.var.args
$request_method	Indicates the request method.	ngx.var.request_method
$request_uri	The content of `uri+'?'+args`.	ngx.var.request_uri
$remote_addr	The IP address of the client that sends the request.	ngx.var.remote_addr

Note

The dollar sign ($) before a variable is used to specify that the variable is a built-in variable. You can remove the dollar sign based on your business requirements.
Do not assign values to built-in variables in the same way as parameters.
You can specify at most 200 global variables and an unlimited number of local variables in a script. To specify more than 200 global variables in a script, create a custom function and use the global variables as local variables in the function.