# Mapping And Variables

Use mapping when the upstream needs transformed headers or query params rather than the original client request.

**Last reviewed:** 2026-03-06

## When to use this

Use this approach when you want a config-first Cloudflare Worker gateway behavior that is already implemented in the repository and covered by tests or canonical examples.

## What this does not do

* It does not add unsupported product features such as rate limiting, caching, API keys, analytics, or OpenAPI generation.
* It does not replace upstream application logic that still belongs in your services.
* It does not remove the need to validate environment variables, bindings, and route intent before deploy.

## Repo-grounded example

```json
{
  "variables": { "region": "eu-west-1" },
  "paths": [
    {
      "method": "GET",
      "path": "/proxy/{.+}",
      "auth": true,
      "integration": { "type": "http_proxy", "server": "upstream" },
      "mapping": {
        "headers": {
          "x-user-id": "$request.jwt.sub",
          "x-region": "$config.region"
        },
        "query": {
          "source": "$request.query.source"
        }
      },
      "variables": { "api_key": "internal-key" }
    }
  ]
}
```

This example is grounded in the current implementation shape: JSON config, path-based routing, optional auth, request mapping, and Worker-native integrations.

## Troubleshooting

* Confirm the route path and HTTP method match what the worker receives.
* Confirm the config source is the one you expect: local file, KV, or `SAG_API_CONFIG_JSON`.
* Confirm required bindings and environment variables are present before debugging downstream logic.
* Run the existing tests in the main gateway repo when a config change appears correct but runtime behavior disagrees.

## Related docs

* [README](https://docs.serverlessapigateway.com/configuration/variable-mapping)
* [priority variables](https://docs.serverlessapigateway.com/configuration/priority-variables)
* [gateway troubleshooting matrix](https://docs.serverlessapigateway.com/troubleshooting/wrangler-deploy-guide/gateway-troubleshooting-matrix)