Healthcheck configuration #

On roles that are running Traefik, Kamal will supply a default healthcheck to docker run. For other roles, by default no healthcheck is supplied.

If no healthcheck is supplied and the image does not define one, they we wait for the container to reach a running state and then pause for the readiness delay.

The default healthcheck is curl -f http://localhost:<port>/<path>, so it assumes that curl is available within the container.

Healthcheck options #

These go under the healthcheck key in the root or role configuration.

healthcheck:

Command #

The command to run, defaults to curl -f http://localhost:<port>/<path> on roles running Traefik

  cmd: "curl -f http://localhost"

Interval #

The Docker healthcheck interval, defaults to 1s

  interval: 10s

Max attempts #

The maximum number of times we poll the container to see if it is healthy, defaults to 7 Each check is separated by an increasing interval starting with 1 second.

  max_attempts: 3

Port #

The port to use in the healthcheck, defaults to 3000

  port: "80"

Path #

The path to use in the healthcheck, defaults to /up

  path: /health

Cords for zero-downtime deployments #

The cord file is used for zero-downtime deployments. The healthcheck is augmented with a check for the existance of the file. This allows us to delete the file and force the container to become unhealthy, causing Traefik to stop routing traffic to it.

Kamal mounts a volume at this location and creates the file before starting the container. You can set the value to false to disable the cord file, but this loses the zero-downtime guarantee.

The default value is /tmp/kamal-cord

  cord: /cord

Log lines #

Number of lines to log from the container when the healthcheck fails, defaults to 50

  log_lines: 100