Docker container specifications

There are two ways to describe a Docker container's launch configuration:

• COI specification that allows you to run only one Docker container.
• Docker Compose specification that allows you to set a more flexible configuration, such as running multiple Docker containers and the required services.

COI specificationCOI specification

In a Container Optimized Image, the Docker container is described in a specification (YAML file) based on a Kubernetes pod spec.

When creating a VM from a Container Optimized Image in the management console or YC CLI, the specification file is generated automatically using the specified data. When creating an instance group from a Container Optimized Image, you set the specification manually. A sample specification file and required keys are described below.

Sample COI specification of a Docker containerSample COI specification of a Docker container

The COI specification is a YAML file with the following contents:

spec:
  containers:
  - command:
    - sleep
    args:
    - 100000
    env:
    - name: MYENV
      value: myvalue
    image: cr.yandex/mirror/ubuntu:16.04
    name: my-container
    securityContext:
      privileged: false
    stdin: false
    tty: false
    volumeMounts:
      - mountPath: /home/yc-user/cache
        name: cache-volume
      - mountPath: /home/yc-user/data
        name: data-volume
  restartPolicy: Always
  volumes:
    - name: cache-volume
      emptyDir:
        medium: Memory
    - name: data-volume
      hostPath:
        path: /data

Where:

• command: Command executed when starting the Docker container.
• args: Arguments sent to the command running in the Docker container.
• env: Environment variables available in the Docker container.
• image: Docker image used to create and run the Docker container.
• name: Docker container to run.
• securityContext: Security and access control settings inside the Docker container. You can only run a privileged Docker container.
• privileged: Run the Docker container in privileged mode. Processes in privileged Docker containers can access any system device and are the same as those with root permissions on a VM. The default value is false.
• stdin: Buffer for the input stream while running the Docker container. The input stream will be linked to the running Docker container. The default value is false.
• tty: Allocate a TTY to the Docker container. The default value is false.
• restartPolicy: Docker container restart policy.
• volumeMounts: List of volumes to mount inside the Docker container.
• mountPath: Path in the Docker container to mount the volume at.
• volumes: Description of the volumes used in the specification.
• emptyDir: Empty directory in the tmpfs temporary file system created in the VM RAM. The contents of this directory are deleted when the Docker container it is mounted to is stopped or when the VM is restarted. To use tmpfs, make sure to specify the medium: Memory parameter. Volume size cannot be greater than the amount of RAM allocated to the VM.
• hostPath: VM file system directory to mount in the Docker container.
• path: Path to the hostPath directory.

Docker Compose specificationDocker Compose specification

You need to provide instructions on running Docker containers and service configurations in the docker-compose.yaml specification file, as stated in this Compose file reference.

For more information on how to run multiple Docker containers, see Creating a VM from a Container Optimized Image with multiple Docker containers.

Sample Docker Compose specificationSample Docker Compose specification

The Docker Compose specification is a YAML file named docker-compose.yaml with the following contents:

version: '3.7'
services:
  app1:
    container_name: nginx
    image: "nginx"
    ports:
      - "80:80"
    restart: always
  app2:
    container_name: redis
    image: "redis"
    restart: always
    volumes:
      - /mnt/logs:/logs
      - /mnt/data:/data

x-yc-disks:
  - device_name: compute-disk-data
    fs_type: ext4
    host_path: /mnt/data
    partition: 1
  - device_name: compute-disk-data
    fs_type: ext4
    host_path: /mnt/logs
    partition: 2

Where:

• version: Specification version tag the file should start with.
• services: Section describing the services.
• container_name: Docker container to run.
• image: Docker image used to create and run the Docker container.
• ports: Used for redirecting service ports. Use this format: <PC_port>:<container_port>.
• restart: Docker container restart policy settings.
• volumes: Description of the volumes used in the Docker container.
• x-yc-disks: Section describing the disks to attach. It is an extension of the Docker Compose specification. Used when preparing to run Docker containers, before running the Docker Compose file. Docker Compose skips this section.
• device_name: Device name, different from the disk name. It is used on the VM to locate the disk in the /dev/disk/by-id/virtio-<device_name> tree. You can set the device-name parameter in flags and CLI commands for adding disks to a VM or in the management console when attaching a disk to a VM.
• fs_type: File system type. The supported file systems are ext4 and xfs.
• host_path: Directory to mount the disk to.
• partition: Disk partition being used.