Deploying containers on single node docker nodes with compose

Jon Brookes - 2020-11-13 12:32

When deploying containers in Docker, possibly for later use in orchestration platforms such as Swarm, K8s, OpenShift it is common to want to test run a docker container firstly on a local service such as a laptop, workstation or stand alone server hosting docker containers.

It may be desirable to stop at this point and not to go to full cluster load balanced and high availability as is afforded by the likes of K8s as a ‘one off’ or ‘private’ implementation of an application does not necessarily need this degree of automation.

docker-compose files serve as a bridge between the one-off and full blown HA implementations and can be used to define single or multiple docker based containers within a package of applications each configured to work as a whole and as a step beyond single Dockerfiles.

Without this, we could use single Dockerfiles for which ‘docker run’ commands are marshalled with command lines and scripts. However this can lack consistency and does not lend itself as well to sharing and re-use as can a compose file.

Prerequisites

  • A working Docker server
  • docker-compose

Example use of compose

An example of using docker-compse is to be found in this gogs-private-repo application.

It uses a single docker-compose.yaml file ( see here ) to define a working application that consists of 2 Docker containers which are each persisted locally mounted volumes :

version: "3.8"
services:
  repo:
    build: ./repo
    ports:
      - "3333:3333"
    volumes:
    - ./repo/data:/app/gogs/data
    - ./repo/repositories:/app/gogs/repositories
    - ./repo/custom/conf:/app/gogs/custom/conf   
    restart: always 
  webhook:
    build: ./webhookapp
    ports:
      - "4000:4000"  
    volumes:
    - ./webhookapp/scripts:/app/scripts
    environment:
      - SYSTEM_COMMAND="/app/scripts/do_something.sh"
    restart: always

Whilst relatively short in length, the above compose file defines several key features that would each lead to separate command line arguments fed to multiple docker run commands.

services : defines 1 or more docker container services, something similar to ‘services’ as a concept in other orchestration platforms.

There are here 2 such services, each with

  • build directories - which is the relative path to where each Dockerfile is located
  • ports list - of 1 or more port mappings, the same as -p in docker run commands
  • volumes list - of 1 or more volumes here mapped to local file storage
  • restart flag to tell docker to start failing containers

environment used in the 2nd container is a list of 1 or more environment variables that are passed to the starting container - the same as -e in docker run commands.

This docker-compose-yaml file is created on a docker server with a single command :

docker-compose up -d

the -d switch tells the compose binary to run the containers in detached mode and to give back the terminal to the user rather than ‘blocking’ and waiting for to break the session.

docker-compose stop

will, as it suggests, stop the running containers and

docker-compose down

will shut down and remove the running containers together with any internal volumes or networks associated with this compose file.

in this example a nice thing to get for free is that a network is automatically created by docker-compose for the current docker-compose.yaml file

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