# Port Forwarding Port forwarding lets developers securely access processes on their Coder workspace from a local machine. A common use case is testing web applications in a browser. There are three ways to forward ports in Coder: - The `coder port-forward` command - Dashboard - SSH The `coder port-forward` command is generally more performant. ## The `coder port-forward` command This command can be used to forward TCP or UDP ports from the remote workspace so they can be accessed locally. Both the TCP and UDP command line flags (`--tcp` and `--udp`) can be given once or multiple times. The supported syntax variations for the `--tcp` and `--udp` flag are: - Single port with optional remote port: `local_port[:remote_port]` - Comma separation `local_port1,local_port2` - Port ranges `start_port-end_port` - Any combination of the above ### Examples Forward the remote TCP port `8080` to local port `8000`: ```console coder port-forward myworkspace --tcp 8000:8080 ``` Forward the remote TCP port `3000` and all ports from `9990` to `9999` to their respective local ports. ```console coder port-forward myworkspace --tcp 3000,9990-9999 ``` For more examples, see `coder port-forward --help`. ## Dashboard > To enable port forwarding via the dashboard, Coder must be configured with a > [wildcard access URL](../admin/configure.md#wildcard-access-url). If an access > URL is not specified, Coder will create [a publicly accessible URL](../admin/configure.md#tunnel) > to reverse proxy the deployment, and port forwarding will work. There is a > known limitation where if the port forwarding URL length is greater than 63 > characters, port forwarding will not work. ### From an arbitrary port One way to port forward in the dashboard is to use the "Port forward" button to specify an arbitrary port. Coder will also detect if processes are running, and will list them below the port picklist to click an open the running processes in the browser. ![Port forwarding in the UI](../images/port-forward-dashboard.png) ### From an coder_app resource Another way to port forward is to configure a `coder_app` resource in the workspace's template. This approach shows a visual application icon in the dashboard. See the following `coder_app` example for a Node React app and note the `subdomain` and `share` settings: ```hcl # node app resource "coder_app" "node-react-app" { agent_id = coder_agent.dev.id slug = "node-react-app" icon = "https://upload.wikimedia.org/wikipedia/commons/a/a7/React-icon.svg" url = "http://localhost:3000" subdomain = true share = "authenticated" healthcheck { url = "http://localhost:3000/healthz" interval = 10 threshold = 30 } } ``` Valid `share` values include `owner` - private to the user, `authenticated` - accessible by any user authenticated to the Coder deployment, and `public` - accessible by users outside of the Coder deployment. ![Port forwarding from an app in the UI](../images/coderapp-port-forward.png) ### Cross-origin resource sharing (CORS) When forwarding via the dashboard, Coder automatically sets headers that allow requests between separately forwarded applications belonging to the same user. When forwarding through other methods the application itself will need to set its own CORS headers if they are being forwarded through different origins since Coder does not intercept these cases. See below for the required headers. #### Authentication Since ports forwarded through the dashboard are private, cross-origin requests must include credentials (set `credentials: "include"` if using `fetch`) or the requests cannot be authenticated and you will see an error resembling the following: > Access to fetch at 'https://coder.example.com/api/v2/applications/auth-redirect' from origin 'https://8000--dev--user--apps.coder.example.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled. #### Headers Below is a list of the cross-origin headers Coder sets with example values: ``` access-control-allow-credentials: true access-control-allow-methods: PUT access-control-allow-headers: X-Custom-Header access-control-allow-origin: https://8000--dev--user--apps.coder.example.com vary: Origin vary: Access-Control-Request-Method vary: Access-Control-Request-Headers ``` The allowed origin will be set to the origin provided by the browser if the users are identical. Credentials are allowed and the allowed methods and headers will echo whatever the request sends. #### Configuration These cross-origin headers are not configurable by administrative settings. If applications set any of the above headers they will be stripped from the response except for `Vary` headers that are set to a value other than the ones listed above. In other words, CORS behavior through the dashboard is not currently configurable by either admins or users. #### Allowed by default
From Alice Bob
Workspace 1 Workspace 2 Workspace 3
To App A App B App C App D
Alice Workspace 1 App A ✅ ✅* ✅* ❌
App B ✅* ✅ ✅* ❌
Workspace 2 App C ✅* ✅* ✅ ❌
Bob Workspace 3 App D ❌ ❌ ❌ ✅
> '\*' means `credentials: "include"` is required ## SSH First, [configure SSH](../ides.md#ssh-configuration) on your local machine. Then, use `ssh` to forward like so: ```console ssh -L 8080:localhost:8000 coder.myworkspace ``` You can read more on SSH port forwarding [here](https://www.ssh.com/academy/ssh/tunneling/example).