Traefik

Traefik is a reverse proxy, used by Kamal for zero-downtime deployments.

We start an instance on the hosts in it's own container.

During a deployment:

1. We start a new container which Traefik automatically detects due to the labels we have applied
2. Traefik starts routing traffic to the new container
3. We force the old container to fail it's healthcheck, causing Traefik to stop routing traffic to it
4. We stop the old container

Traefik settings

Traekik is configured in the root configuration under traefik.

traefik:

Image

The Traefik image to use, defaults to traefik:v2.10:

  image: traefik:v2.9

Host port

The host port to publish the Traefik container on, defaults to 80:

  host_port: "8080"

Disabling publishing

To avoid publishing the Traefik container, set this to false:

  publish: false

Labels

Additional labels to apply to the Traefik container:

  labels:
    traefik.http.routers.catchall.entryPoints: http
    traefik.http.routers.catchall.rule: PathPrefix(`/`)
    traefik.http.routers.catchall.service: unavailable
    traefik.http.routers.catchall.priority: "1"
    traefik.http.services.unavailable.loadbalancer.server.port: "0"

Arguments

Additional arguments to pass to the Traefik container:

  args:
    entryPoints.http.address: ":80"
    entryPoints.http.forwardedHeaders.insecure: true
    accesslog: true
    accesslog.format: json

Options

Additional options to pass to docker run:

  options:
    cpus: 2

Environment variables

See Environment variables:

  env:
    ...