Docker Service

Zerops provides Docker support through dedicated Virtual Machine (VM) environments, ensuring maximum compatibility and isolation while maintaining integration with the broader Zerops ecosystem. This guide explains how to effectively use Docker services on Zerops, including best practices and important considerations.

Why VMs

While Zerops primarily uses native Linux containers for optimal performance, this VM-based approach allows you to run virtually any Docker container while maintaining Zerops' robust infrastructure management.

You can learn more about differences between Containers and Virtual Machines on Zerops.

Before using Docker services, consider these important aspects:

Virtual Machine Environment

Docker services on Zerops operate in a full VM environment, which has several implications:

• Slower Boot Times: VMs require more time to initialize due to full kernel boot
• Higher Resource Usage: VMs include additional system overhead compared to native containers
• Scaling Limitations:
  • Vertical scaling requires VM restart
  • Resources must be set as fixed values (no min-max ranges)
  • Zerops automatically restarts the VM when resource values are changed in UI
• Storage Management: Disk space can only be increased, not decreased without recreation
• Build Phase Limitations: Build phase runs in containers, not in the VM environment

Advantages

Despite these limitations, Docker services offer some benefits:

• Broad Compatibility: Run almost any Docker container with minimal modification
• Familiar Environment: Standard Docker runtime environment

Configuration Guide

Supported Version

Currently supported Docker versions:

• docker@26.1.5

Basic Structure

Docker services in Zerops are configured through the zerops.yml file. Here's a typical configuration pattern:

zerops.yml

zerops:
  - setup: app
    run:
      prepareCommands:
        - docker image pull <your-image>
      start: docker run --network=host <your-image>
      ports:
        - port: <port-number>
          httpSupport: true

Refer to the Docker recipe repository for an example configuration.

Note

We are actively working on improving the speed of image caching after run.prepareCommands and reducing the startup time of runtime VMs. These improvements will be released in future updates.

Network Configuration

Docker services require the --network=host flag for proper integration with Zerops:

• Direct Port Management: Ports are managed through zerops.yml
• Simplified Configuration: Avoids double port exposure in Docker and Zerops
• Native Performance: Direct access to host networking

Docker Compose Support

For projects using Docker Compose, additional configuration is required:

1. File Deployment:

   zerops.yml

   build:
     deployFiles: ./docker-compose.yml
     addToRunPrepare: ./docker-compose.yml

2. Network Mode:

   docker-compose.yml

   services:
     your-service:
       network_mode: host

Implementation Examples

Single Container

zerops.yml

zerops:
  - setup: app
    run:
      prepareCommands:
        - docker image pull crccheck/hello-world
      start: docker run --network=host crccheck/hello-world
      ports:
        - port: 8000
          httpSupport: true

Single Service with Docker Compose

zerops.yml

zerops:
  - setup: api
    build:
      deployFiles: ./docker-compose.yml
      addToRunPrepare: ./docker-compose.yml
    run:
      prepareCommands:
        - docker compose pull api
      start: docker compose up api --force-recreate
      ports:
        - port: 8000
          httpSupport: true

Multiple Services with Docker Compose

zerops.yml

zerops:
  - setup: apps
    build:
      deployFiles: ./docker-compose.yml
      addToRunPrepare: ./docker-compose.yml
    run:
      prepareCommands:
        - docker compose pull
      start: docker compose up --force-recreate
      ports:
        - port: 8000
          httpSupport: true

Best Practices

Image Management

• Use prepareCommands for image pulling
• Consider using specific image tags instead of latest

Resource Planning

• Account for VM overhead in resource allocation
• Plan for longer initialization times
• Consider the impact on scaling operations

Migration Consideration

• Evaluate if your workload could run on native containers
• Consider gradual migration for complex applications
• Balance development effort against operational benefits

Limitations and Workarounds

Build Phase

Since the build phase runs in containers rather than VMs:

• Use run.prepareCommands for Docker-specific build steps
• Consider external CI/CD for complex Docker builds
• Leverage pre-built images when possible

Scaling Operations

Docker services on Zerops have specific scaling characteristics that differ from native containers:

Vertical Scaling

• Resources must be defined with fixed values instead of min-max ranges
• CPU, RAM, and disk are specified as single values:

  verticalAutoscaling:
    cpu: 3
    ram: 2
    disk: 20
• Any change to these values through the UI triggers an automatic VM restart
• Plan your resource allocation carefully to minimize scaling operations

Horizontal Scaling

• Still supports multiple containers through minContainers and maxContainers
• Consider breaking large services into smaller components
• Implement proper health checks for reliable scaling
• Use horizontal scaling when possible to avoid VM restarts