Built-In Variables

Built-in variables in APISIX are pre-defined variables that can be directly referenced in configurations. They are often used in plugin configurations, route matching, and log customization.

APISIX supports three types of built-in variables:

• NGINX Variables
• APISIX Variables
• Custom Variables

These variables are evaluated in a given order.

NGINX Variables

NGINX provides a set of variables that can be used to access various request-specific information.

Some of the commonly used variables include:

• upstream_addr
• remote_addr
• request_uri
• server_name
• uri
• http_user_agent

See the complete list of NGINX variables for more information.

APISIX Variables

In addition to NGINX variables, APISIX offers a variety of built-in variables:

Variable Name	Description
post_arg_*	HTTP POST form data when the content type is application/x-www-form-urlencoded. The asterisk is to be replaced with the actual name of the POST form data.
arg_*	URL query string. The asterisk is to be replaced with the actual query parameter name.
http_*	HTTP request header. The asterisk is to be replaced with the actual name of the header.
cookie_*	Request cookie. The asterisk is to be replaced with the actual name of the cookie.
balancer_ip	Upstream server IP.
balancer_port	Upstream server port.
consumer_name	Consumer username.
consumer_group_id	Consumer group ID.
graphql_name	GraphQL operation name.
graphql_operation	GraphQL operation type.
graphql_root_fields	GraphQL root fields.
route_id	Route ID.
route_name	Route name.
service_id	Service ID.
service_name	Service name.
resp_body	HTTP response body.
mqtt_client_id	Client ID in MQTT protocol.
redis_cmd_line	Redis command.
rpc_time	RPC request round-trip time.

Custom Variables

You can also register your own variables and use them as built-in variables. For instance, you can use custom variables to customize log format in logging plugins, or use them as keys in rate limiting plugins.

Example

The following example demonstrates two approaches for custom variable registration and how you can leverage the variable to obtain information from a route, subsequently logging the information to a remote server.

Create a Service

Create a service to configure http-logger plugin and upstream:

curl http://127.0.0.1:9180/apisix/admin/services -X PUT \
  -H 'X-API-KEY: ${ADMIN_API_KEY}' \
  -d '{
    "id":"srv_custom_var",
    "plugins": {
      "http-logger": {
        "uri": "'"${REMOTE_SERVER_ADDR}"'"
      }
    },
    "upstream": {
      "nodes": {
        "httpbin.org:80": 1
      }
    }
  }'

Register a Custom Variable

You can choose to register the custom variable in the source code or use the serverless plugins.

Method 1: In the Source Code

Add the following snippet to your custom Lua file and source it to register a custom variable named a6_route_labels. The variable represents the value of labels in a request to a route, if available:

local core = require "apisix.core"

core.ctx.register_var("a6_route_labels", function(ctx)
  local route = ctx.matched_route and ctx.matched_route.value
  if route and route.labels then
    return route.labels
  end
  return nil
end)

Start or reload APISIX accordingly. If APISIX is already running, send a PUT request to /apisix/admin/plugins/reload to hot reload the plugins for changes to take effect.

caution

While the snippet can technically be added anywhere the code is sourced, exercise caution when modifying the APISIX core codebase to avoid any negative impact on the standard functionalities.

It is recommended to keep your custom Lua code in a separate directory and source it by configuring extra_lua_path and extra_lua_cpath in the config.yaml configuration file.

For more information, see create Lua plugin guide.

Method 2: In the serverless Plugins

You can also register a custom variable using the serverless-pre-function or serverless-post-function plugins. These plugins run serverless functions before or after a specified execution phase, and you can register custom variables in these functions.

Add the serverless-pre-function plugin to the previously created service, where the function registers the custom variable a6_route_labels:

curl http://127.0.0.1:9180/apisix/admin/services/srv_custom_var -X PATCH \
  -H 'X-API-KEY: ${ADMIN_API_KEY}' \
  -d '{
    "plugins": {
      "serverless-pre-function": {
        "phase": "rewrite",
        "functions": [
          "return function()
            local core = require \"apisix.core\"
            core.ctx.register_var(\"a6_route_labels\", function(ctx)
              local route = ctx.matched_route and ctx.matched_route.value
              if route and route.labels then
                return route.labels
              end
              return nil
            end); 
          end"
        ]
      }
    }
  }'

Configure Log Format

Create a plugin metadata object to configure log format for all http-logger instances:

curl http://127.0.0.1:9180/apisix/admin/plugin_metadata/http-logger -X PUT \
  -H 'X-API-KEY: ${ADMIN_API_KEY}' \
  -d '{
    "log_format": {
      "host": "$host",
      "client_ip": "$remote_addr",
      "labels": "$a6_route_labels"
    }
  }'

❶ host and remote_addr: NGINX variables.

❷ a6_route_labels: custom variable.

Create a Route in Service

Create a route in the service:

curl http://127.0.0.1:9180/apisix/admin/routes -X PUT \
  -H 'X-API-KEY: ${ADMIN_API_KEY}' \
  -d '{
    "id":"route_custom_var",
    "uri":"/get",
    "service_id": "srv_custom_var",
    "labels": {
      "key": "test_a6_route_labels"
    }
}'

❶ service_id: correspond to the previously created service.

❷ labels: route information to be logged with the custom variable.

Verify Custom Variable Registration

Send a request to verify that the custom variable logs the labels information in route:

curl http://127.0.0.1:9080/get

You should see a log entry in your remote server created by a POST request with a body similar to the following:

[
  {
    "labels": {
      "key": "test_a6_route_labels"
    },
    "service_id": "srv_custom_var",
    "client_ip": "172.21.0.1",
    "route_id": "route_custom_var",
    "host": "127.0.0.1"
  }
]

This verifies the custom variable was registered and it logs the labels information in a route successfully.

Evaluation Order

APISIX evaluates variables in the given order:

1. Custom Variables
2. APISIX Variables
3. NGINX Variables

If a variable is successfully sourced in custom variables, APISIX will not continue to look in APISIX variables or NGINX variables.

In other words, custom variables will overwrite variables of the same names defined in APISIX variables or NGINX variables, to better meet requirements of your specific use cases.