Port Forwarding

NOTE: If you’re planning on continuing to the DNS section, you can skip this.

In devcontainer.json, there’s a section for forwardPorts; this is what we use for forwarding ports. However, we do not pay attention to portsAttributes; forwarding ports with devconcurrent is an explicit action, so the semantics are a bit different than with a long-lived editor.

When ports are forwarded, services in containers see requests from the host as coming from localhost. This is accomplished by creating two thin docker sidecars; one inside the target’s network namespace, and one that listens to the port on the host.

Managing ports is cumbersome and error-prone; it’s easy to forget which workspace has the ports at any moment. Instead, in the next sections, we’ll cover accessing the containers by hostname so you never have to do this.

Commands

dc fwd

Start forwarding ports for the current workspace (or one given by `-w/–workspace).

If any ports are already forwarded by devconcurrent, they are moved to this workspace. If any are already in use by something else, we log a warning and forward what we can.

This allows you to “move” ports to the current workspace with a simple dc f.

dc fwd stop

Stop forwarding ports.

dc show ports

Show what ports are being forwarded to the current workspace; this can be useful in a shell prompt if you’d like a reminder if you’re currently forwarding here.