Docker Compose Wait for Dependencies

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Docker Compose Wait for Postgres Container to be Ready

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Docker Compose Wait for Dependencies

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This article provides an example for making docker-compose wait for Postgres or Postgresql container to be ready before starting a dependent docker application container. We’ll use the docker-compose-wait tool tool, which is a small command line utility allowing to wait for a fixed amount of seconds and/or to wait until a TCP port is open on a target image.

You need to add the docker-compose-wait tool in your application Dockerfile.



Contents:

Quick start

# Download a template
git clone https://github.com/kassambara/docker-compose-wait-for-container.git

# Build the demo application
cd docker-compose-wait-for-container/ex01-using-wait-tool
docker-compose build
# Running your app
docker-compose run my_super_app

# Stopping containers and cleaning
docker-compose down

Step 0: Download a template

# Download a template
git clone https://github.com/kassambara/docker-compose-wait-for-container.git
cd docker-compose-wait-for-container/ex02-using-wait-tool

Project folder structure:

files/docker-compose-wait-for-container/ex01-using-wait-tool
├── docker-compose.yml
└── my_super_app
    ├── Dockerfile
    └── sayhello

Essential project contents:

  • docker-compose.yml to run all container services
  • my_super_app scripts: template Dockerfile to build your application. Here, this demo app will ask your name and then congratulate you!

Step 1: Add the docker-compose-wait tool to your application Dockerfile

Example of Dockerfile using the alpine image:

FROM alpine:latest

# Add hello scripts
ADD sayhello /sayhello
RUN chmod +x /sayhello

# Add docker-compose-wait tool -------------------
ENV WAIT_VERSION 2.7.2
ADD https://github.com/ufoscout/docker-compose-wait/releases/download/$WAIT_VERSION/wait /wait
RUN chmod +x /wait

CMD ["/sayhello"]

Step 2: Modify your docker-compose.yml file

version: '3.6'
services:
  postgres:
    image: "postgres:9.4"
    hostname: postgres
    ports:
      - "5432:5432"

  my_super_app:
    build: ./my_super_app
    image: "my_super_app:latest"
    container_name: my_supper_app
    depends_on:
      - postgres
    command: sh -c "/wait && /sayhello"
    environment:
      - WAIT_HOSTS=postgres:5432
      - WAIT_HOSTS_TIMEOUT=300
      - WAIT_SLEEP_INTERVAL=30
      - WAIT_HOST_CONNECT_TIMEOUT=30
  • The command sh -c “/wait && /sayhello” will run the wait tool and then your application, here /sayhello.
  • To make your docker application container wait for multiple hosts, the environment variable can be specified as for example WAIT_HOSTS=postgres:5432, nginx:80

Additional configuration options. The behavior of the wait utility can be configured with the following environment variables:

  • WAIT_HOSTS: comma separated list of pairs host:port for which you want to wait.
  • WAIT_HOSTS_TIMEOUT: max number of seconds to wait for all the hosts to be available before failure. The default is 30 seconds.
  • WAIT_HOST_CONNECT_TIMEOUT: The timeout of a single TCP connection to a remote host before attempting a new connection. The default is 5 seconds.
  • WAIT_BEFORE_HOSTS: number of seconds to wait (sleep) before start checking for the hosts availability
  • WAIT_AFTER_HOSTS: number of seconds to wait (sleep) once all the hosts are available
  • WAIT_SLEEP_INTERVAL: number of seconds to sleep between retries. The default is 1 second.

Step 3: Building and running your app

# Building your app
cd docker-compose-wait-for-container/ex01-using-wait-tool
docker-compose build
# Running your app
docker-compose run my_super_app

Console log output looks like this (MySQL example):

Docker compose wait logs

After typing your name, you will see a congratulation message from my_super_app

Step 4: Stopping containers and cleaning

docker-compose down

Summary

This article describes how to make docker-compose wait for Postgres or Postgresql container using the docker-compose-wait tool.



 
          

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