Expose a Docker container

Share a web app that runs in a Docker container, with an HTTPS URL. You run hrzn on your host, not in the container.

Before you beginCopy Anchor Link

• Node.js 18 or later
• A Horizon account and the CLI on your host (see Getting started)
• A reserved subdomain for -s. Reserve one on the Subdomains page.
• Docker, and an image whose app listens on port 3000

docker run -d -p 3000:3000 my-image

docker run -d -p 127.0.0.1:3000:3000 my-image

curl http://localhost:3000

hrzn tunnel http://localhost:3000 -s my-app

HORIZON: Tunnel connected
  URL          https://my-app.hrzn.run (reserved)
  Forwarding   http://localhost:3000
  Request log  https://hrzn.run/dashboard/tunnels/my-app

Check it worksCopy Anchor Link

The Horizon terminal prints a line per request:

  GET     200  /

Horizon sets Host to localhost:3000, so your app sees the host the container's port is published on. The public host arrives in X-Forwarded-Host.

TroubleshootingCopy Anchor Link

Bind for 0.0.0.0:3000 failed: port is already allocatedCopy Anchor Link

Another container or process holds host port 3000. Publish a different host port, for example -p 3001:3000, and tunnel to http://localhost:3001.

Nothing reaches your appCopy Anchor Link

• Check that the Horizon terminal is still running. If its last line is Connection lost. Reconnecting…, wait for Reconnected.
• Run curl http://localhost:3000 on the host. If it fails, the problem is the container, not the tunnel. Run docker ps and check the PORTS column.
• The tunnel target is the host port, the left side of -p.

The URL changed after a restartCopy Anchor Link

You started the tunnel without -s, so Horizon gave you a new random subdomain. Restart with -s my-app.

Next stepsCopy Anchor Link

• Use the same flow with Docker Compose.