Multi-container applications

Tomáš Tomeček

Recap

1. What is a linux container?
2. Do you store persistent data in a container?
3. Can I control resources for containers?
4. How do I set some environment variables inside container?

Single-container app

Static web-page.

$ docker run -d -p 1313:1313 -t lgsd/docker-hugo
          

Single-container app

• Can be run with a single command.
• Storage is easy.
• Networking within a single host.
• Management can be manual.
• Monitoring (one process).
• Zero-downtime upgrades should be easily possible.

Multi-container app

• Web.
• Database.
• In-memory database.
• Worker.

Multi-container app

• It takes several commands to start all services.
• Start order matters.
• Storage is hard.
• Networking is harder.
• Services may not run on the same host.
• Services may not run in the same cluster.
• Services may not run in the same data center.
• Services may not run in the same region.
• Oh my! How do I manage this?
• ...and how do I monitor it?!
• I wish we had zero-downtime upgrades.

Orchestration

• Application definition
• Storage
• Networking (PaaS)
• Management
• Service discovery (PaaS)
• Content?

Application definition

• Image
• Ports
• Volumes
• Environment variables
• Security (users, permissions, capabilities)

Container content

• How do I create my image?
• Support
• Security updates

Storage

• Volumes
• Volume types

Management

• How do I get images?
• How do I deploy?
• How do I update?
• How do I scale?

Multi-container tools

• kubernetes
• docker-compose
• ansible-container

docker-compose

version: '2'
services:
  web:
    build: .
    ports:
    - "5000:5000"
    volumes:
    - .:/code
    - data_volume:/data
    links:
    - redis
  redis:
    image: redis
volumes:
  data_volume: {}
          

Demo

• swa-fel/03-multi-container-apps