Controlling Container Startup Order with Dockerize in Docker Compose

This article was originally published on bmf-tech.com.

Overview

This is a note on how to control the startup order of containers launched with Docker Compose using Dockerize.

github.com - jwilder/dockerize

Why Use Dockerize

It is also possible to use a pure bash script called wait-for-it instead of Dockerize.

cf. Docker-docs-ja - Controlling Startup Order

The purpose of using Dockerize is when you want to intentionally control the startup order of multiple containers.

For example, if there is an application container and a test database container, the database container needs to start before the application container when the application container performs tests that use the DB.

In short, it aims to resolve the dependency of the startup order between containers.

Docker Compose has options like depends_on and links, but depends_on controls the creation order of containers, while links performs name resolution between containers in addition to the functionality of depends_on, but neither controls the startup order.

I later learned that links is automatically executed from version 2 onwards and has become legacy.

Example

Here is an example from one of my applications.

docker-compose.yml

version: "3"
services:
  gobel_app:
    container_name: "gobel_app"
    build: ./docker/go
    volumes:
      - ./app:/go/src/github.com/bmf-san/Gobel/app
    ports:
      - "8080:8080"
    depends_on:
      - gobel_db
      - gobel_test_db
    entrypoint:
      - dockerize
      - -timeout
      - 10s
      - -wait
      - tcp://gobel_test_db:3306
    command: realize start
  gobel_db:
    container_name: "gobel_db"
    build: ./docker/mysql
    ports:
      - "3306:3306"
    volumes:
      - mysql_gobel_db:/var/lib/mysql:delegated
      - ./docker/mysql/initdb.d/gobel_db:/docker-entrypoint-initdb.d
    environment:
      - MYSQL_DATABASE=gobel
      - MYSQL_ROOT_PASSWORD=password
  gobel_test_db:
    container_name: "gobel_test_db"
    build: ./docker/mysql
    ports:
      - "3305:3306"
    volumes:
      - mysql_gobel_test_db:/var/lib/mysql:delegated
      - ./docker/mysql/initdb.d/gobel_test_db:/docker-entrypoint-initdb.d
    environment:
      - MYSQL_DATABASE=gobel_test
      - MYSQL_ROOT_PASSWORD=password
volumes:
  mysql_gobel_db:
    driver: local
  mysql_gobel_test_db:
    driver: local

gobel_app container wants to wait for the startup of gobel_test_db.
The entrypoint specifies the dockerize command.

Dockerfile used for building the gobel_app container.

FROM golang:1.13.0-alpine

WORKDIR /go/src/github.com/bmf-san/Gobel/app/

RUN apk add --no-cache git \
    binutils-gold \
    curl \
    g++ \
    gcc \
    gnupg \
    libgcc \
    linux-headers \
    make
RUN go get github.com/go-sql-driver/mysql
RUN go get github.com/oxequa/realize
RUN go get -u golang.org/x/lint/golint
ENV DOCKERIZE_VERSION v0.6.0
RUN apk add --no-cache openssl \
 && wget https://github.com/jwilder/dockerize/releases/download/$DOCKERIZE_VERSION/dockerize-alpine-linux-amd64-$DOCKERIZE_VERSION.tar.gz \
 && tar -C /usr/local/bin -xzvf dockerize-alpine-linux-amd64-$DOCKERIZE_VERSION.tar.gz \
 && rm dockerize-alpine-linux-amd64-$DOCKERIZE_VERSION.tar.gz

It includes the installation of dockerize.

Thoughts

It can be easily introduced.
While it might be fine to prepare a script like wait-for-it on your own, I thought it would be reasonable to include dockerize considering that container management could become more complex.