Docker container specifications

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

• COI specification, which you can use to run a single Docker container.
• Docker Compose specification, which offers more flexibility. For example, you can run multiple Docker containers and services.

COI specifications

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

Creating a VM from a Container Optimized Image in the management console or CLI automatically generates the specification file using the provided data. When creating an instance group from a Container Optimized Image, you set the specification manually. Below are a sample specification file and the required keys.

Example of the COI specification for 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 to run on Docker container launch.
• args: Arguments the command to run in the Docker container gets.
• env: Environment variables available in the Docker container.
• image: Docker image for creating and running a 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 identical to those with root permissions on a VM. The default value is false.
• stdin: Buffer for the input stream while running the Docker container. The system will link the input stream to the running Docker container. The default value is false.
• tty: TTY allocation for the Docker container. The default value is false.
• restartPolicy: Docker container restart policy.
• volumeMounts: List of volumes to mount inside a Docker container.
• mountPath: Path in the Docker container for mounting the specified volume.
• volumes: Description of the volumes the specification file uses.
• emptyDir: Empty directory in the tmpfs temporary file system created in the VM RAM. Stopping the directory Docker container or restarting the VM deletes the contents of this directory. To use tmpfs, make sure to specify the medium: Memory parameter. The size of a volume cannot be greater than the amount of RAM allocated to the VM.
• hostPath: Directory from the VM file system to mount in the Docker container.
• path: hostPath directory path.

Use cases

• Creating a VM and an instance group from a Container Optimized Image using Terraform
• Configuring data output from a Docker container to a serial port

Docker Compose specification

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

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

Example of the Docker Compose specification

The Docker Compose specification is a file named docker-compose.yaml with these 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 for creating and running the Docker container.
• ports: Redirects service ports. Use this format: <PC_port>:<container_port>.
• restart: Docker container restart policy.
• volumes: Description of the volumes the Docker container uses.
• x-yc-disks: Section describing the disks to connect. It is an extension of the Docker Compose specification you use 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. You use it 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 CLI flags and commands for adding disks to a VM or in the management console when connecting 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.

Use cases

• Creating a VM from a Container Optimized Image with multiple Docker containers
• Creating a VM from a Container Optimized Image with an additional volume for a Docker container
• Transferring logs from Container Optimized Image to Yandex Cloud Logging