Accessories

Accessories can be booted on a single host, a list of hosts, or on specific roles. The hosts do not need to be defined in the Kamal servers configuration.

Accessories are managed separately from the main service — they are not updated when you deploy and they do not have zero-downtime deployments.

Run kamal accessory boot <accessory> to boot an accessory. See kamal accessory --help for more information.

Configuring accessories

First define the accessory in the accessories:

yaml

accessories:
  mysql:

Service name

This is used in the service label and defaults to <service>-<accessory> where <service> is the main service name from the root configuration:

yaml

    service: mysql

Image

The Docker image to use, prefix with a registry if not using Docker hub:

yaml

    image: mysql:8.0

Accessory hosts

Specify one of host, hosts or roles:

yaml

    host: mysql-db1
    hosts:
      - mysql-db1
      - mysql-db2
    roles:
      - mysql

Custom command

You can set a custom command to run in the container, if you do not want to use the default:

yaml

    cmd: "bin/mysqld"

Port mappings

See https://docs.docker.com/network/, especially note the warning about the security implications of exposing ports publicly.

yaml

    port: "127.0.0.1:3306:3306"

Labels

yaml

    labels:
      app: myapp

Options

These are passed to the Docker run command in the form --<name> <value>:

yaml

    options:
      restart: always
      cpus: 2

Environment variables

See Environment variables for more information:

yaml

    env:
      ...

Copying files

You can specify files to mount into the container. The format is local:remote where local is the path to the file on the local machine and remote is the path to the file in the container.

They will be uploaded from the local repo to the host and then mounted.

ERB files will be evaluated before being copied.

yaml

    files:
      - config/my.cnf.erb:/etc/mysql/my.cnf
      - config/myoptions.cnf:/etc/mysql/myoptions.cnf

Directories

You can specify directories to mount into the container. They will be created on the host before being mounted:

yaml

    directories:
      - mysql-logs:/var/log/mysql

Volumes

Any other volumes to mount, in addition to the files and directories. They are not created or copied before mounting:

yaml

    volumes:
      - /path/to/mysql-logs:/var/log/mysql